Closed multi-stage washing silicon nitride powder pickling production line and production process

Abstract

This invention discloses a closed-loop, multi-stage washing production line and process for silicon nitride powder, belonging to the field of silicon nitride powder production technology. The production line includes an acid washing unit, an acid recovery unit, a turbid water treatment unit, a multi-stage water washing unit, and a concentrated liquid treatment unit. By adopting a multi-stage continuous washing structure, this invention allows the mixed liquid of fresh washing water and acid to come into contact with the silicon nitride powder containing impurities, which can quickly dissolve and remove the metal impurity ions (Fe3+, Al3+, Ca2+) in the powder particles. In the subsequent stage, fresh washing water is used in a multi-stage continuous manner to gradually dilute and remove the acid radical ions (Cl-, SO42-, F-) in the gaps between powder particles and within agglomerates. This solves the problems of insufficient mass transfer driving force and incomplete washing in the intermittent washing of the prior art.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride powder production technology, specifically relating to a closed-loop multi-stage washing production line and process for silicon nitride powder acid washing. Background Technology

[0002] Currently, the closest existing technology to this application in the production process of silicon nitride powder is the traditional intermittent silicon nitride powder acid washing and purification process and equipment.

[0003] Its technical solution mainly includes: using a reaction vessel or pickling tank as the main equipment, adding silicon nitride powder and acid solution into the tank at one time, and carrying out the pickling reaction by manual or simple stirring; After the reaction is complete, solid-liquid separation is performed by standing, filtration or centrifugation, followed by washing with water in batches and filtering multiple times. After washing until neutral, the powder is unloaded, collected, and then transferred to drying equipment for drying.

[0004] Traditional pickling lines are characterized by dispersed processes, intermittent operation, and open equipment operation, mainly relying on single-tank reaction, manual feeding, and batch filtration and washing.

[0005] However, the aforementioned traditional silicon nitride powder pickling process and equipment have the following obvious drawbacks in actual production: 1. Intermittent operation, low production efficiency, and poor batch stability: Traditional processes involve single-tank batch processing, with feeding, reaction, washing, and unloading all carried out intermittently, resulting in long processing cycles and making it difficult to achieve continuous production. The pickling time, acid concentration, and washing degree between different batches are difficult to keep consistent, leading to large fluctuations in powder purity, oxygen content, and metal ion content.

[0006] 2. Low acid utilization rate, high acid consumption, and high production cost. During the reaction process, the acid and powder are not mixed evenly, and the local reaction is insufficient. A large amount of acid is discharged before it is fully involved in dissolving impurities. At the same time, multiple water changes and washing lead to a large amount of water consumption and waste acid generation, which increases the consumption of raw materials and environmental treatment costs.

[0007] 3. Insufficient washing can leave behind impurity ions, affecting powder quality. Traditional filtration or centrifugal washing has a short path and poor control over residence time. Chloride ions, sulfate ions, fluoride ions, etc., are easy to remain in the gaps between powder particles or in agglomerates. During subsequent sintering, this can easily produce pores, black spots, or grain boundary impurities, reducing the strength and density of silicon nitride ceramics.

[0008] 4. Open or semi-open operation of equipment results in poor safety and environmental protection. Acid mist is easily volatilized and escaped during pickling, creating a highly corrosive environment and a poor working environment, which has an adverse effect on the health of operators and the lifespan of equipment. At the same time, incomplete solid-liquid separation can easily lead to powder loss and environmental pollution.

[0009] 5. Low level of automation, high dependence on manual labor, and difficulty in precise quality control. Feeding, pH detection, water change, and unloading all rely on manual operation. It is impossible to accurately control the acid washing temperature, reaction time, washing endpoint, and slurry concentration online, making it difficult to meet the requirements of high purity, stability, and consistency for high-end silicon nitride powder. Summary of the Invention

[0010] To address the problems mentioned in the background section, this invention provides a closed-loop, multi-stage washing production line for silicon nitride powder, which significantly improves washing efficiency, reduces powder impurities, ensures product quality stability, increases acid and water resource utilization, and substantially reduces production costs and environmental impact.

[0011] The present invention also provides a production process for a closed-loop, multi-stage washing silicon nitride powder pickling production line.

[0012] To achieve the above objectives, the present invention provides the following technical solution: a closed-loop multi-stage washing production line for silicon nitride powder, the production line comprising an acid washing unit, an acid recovery unit, a turbid water treatment unit, a multi-stage water washing unit, and a concentrated liquid treatment unit; The turbid water treatment unit includes a No. 1 turbid water mixing tank, a No. 2 turbid water mixing tank, a No. 1 ceramic membrane device, a No. 2 ceramic membrane device, and a purified water tank. The No. 1 turbid water mixing tank and the No. 2 turbid water mixing tank are respectively connected to the No. 1 ceramic membrane device and the No. 2 ceramic membrane device via turbid water lift pumps. The purified water outlets of the No. 1 ceramic membrane device and the No. 2 ceramic membrane device are both connected to the purified water tank via purified water lift pumps. The No. 1 ceramic membrane forward wash water tank and the No. 2 ceramic membrane forward wash water tank are respectively connected to the No. 1 ceramic membrane device and the No. 2 ceramic membrane device. The multi-stage washing unit includes a No. 1 washing mixing tank, a No. 2 washing mixing tank, a No. 3 washing mixing tank, a No. 4 washing mixing tank, a No. 3 centrifuge, and a No. 4 centrifuge. A pure water storage tank is connected to the No. 1 washing circulating mixing tank, the No. 2 washing circulating mixing tank, the No. 3 washing circulating mixing tank, and the No. 4 washing circulating mixing tank via a pump. The No. 1 washing circulating mixing tank is connected to the No. 1 washing mixing tank via a pump. The No. 2 washing circulating mixing tank is connected to the No. 2 washing mixing tank via a pump. The No. 3 washing circulating mixing tank is connected to the No. 3 washing mixing tank via a pump. The No. 4 washing circulating mixing tank is connected to the No. 4 washing mixing tank via a pump. The outlets of the No. 1 and No. 2 washing mixing tanks merge and are connected to the No. 3 centrifuge. The outlets of the No. 3 and No. 4 washing mixing tanks merge and are connected to the No. 4 centrifuge. The concentrated liquid treatment unit includes a No. 1 waste acid mixing tank, a No. 2 waste acid mixing tank, a No. 1 50% concentrated acid mixing tank, and a No. 2 50% concentrated acid mixing tank. The concentrated liquid outlets of the No. 1 ceramic membrane equipment and the No. 2 ceramic membrane equipment are respectively connected to the No. 1 waste acid mixing tank and the No. 2 waste acid mixing tank. The No. 1 waste acid mixing tank is connected to the No. 1 50% concentrated acid mixing tank and the No. 2 50% concentrated acid mixing tank via the No. 1 concentrated acid lift pump and the No. 2 50% concentrated acid mixing tank via the No. 2 concentrated acid lift pump, respectively. The liquid from the No. 1 50% concentrated acid mixing tank and the No. 2 50% concentrated acid mixing tank is returned to the pickling unit via the No. 1 50% concentrated acid lift pump and the No. 2 50% concentrated acid lift pump, respectively. The outlet of the No. 2 50% concentrated acid lift pump is connected to an external centrifuge. The pure water storage tank is connected to the cleaning interfaces of each mixing tank and pipeline through a tank cleaning pump, a pipeline cleaning pump, and a mixing tank flushing water outlet pump. The clean water tank is returned to the turbid water treatment unit through the turbid water tank unqualified lift pump. The outlet of the entire line of lift pump, circulation pump, outlet pump, water tank, mixing tank and storage tank is equipped with a control valve.

[0013] Furthermore, the outlet of the acid treatment booster pump is connected to an external non-recoverable acid treatment device.

[0014] Furthermore, the pure water storage tank is connected to an external reverse osmosis outlet pipe.

[0015] Furthermore, the inlet of the purified water booster pump is connected to the water supply pipeline of the plant's radiator, and the booster pump for unqualified turbid water tanks is connected to the raw water tank for acid treatment.

[0016] Furthermore, the discharge end of the fourth centrifuge is connected to an external drying device.

[0017] Furthermore, the No. 1 pickling mixing tank and the No. 2 pickling mixing tank of the pickling unit are connected in series in a closed structure, and the inner walls of the mixing tanks are made of corrosion-resistant material.

[0018] Furthermore, the No. 1 and No. 2 ceramic membrane devices of the turbid water treatment unit are connected in parallel and have an online backwashing function.

[0019] Furthermore, the multi-stage washing unit is a four-stage continuous countercurrent washing structure, and each stage of the washing mixing tank is equipped with an online conductivity and pH detection probe.

[0020] Furthermore, centrifuges No. 1, No. 2, No. 3, and No. 4 are all corrosion-resistant, sealed centrifuges.

[0021] A production process for a closed-loop, multi-stage washing line for pickling silicon nitride powder includes the following steps: Preparation of S1 acid solution: ① Hydrochloric acid storage tank control: The hydrochloric acid storage tank is equipped with a magnetic float level gauge (high, medium and low switch signals); under normal operation, when the liquid level reaches the medium level, an alarm will sound to remind you to replenish hydrochloric acid. The acid replenishment is manually controlled by a pneumatic diaphragm pump. ② Hydrochloric acid booster pump / hydrofluoric acid booster pump control: Hydrochloric acid booster pump and hydrofluoric acid booster pump (acid addition) are set up and are manually controlled separately; during normal operation, after hearing the alarm, open the inlet and outlet valves of the booster pump of the corresponding storage tank, start the water pump, and manually stop the water pump after reaching the high liquid level; ③ Hydrochloric acid metering system control: A metering pump (662L / H) is installed at the outlet of the hydrochloric acid storage tank. The outlet pipeline of the metering pump is connected in parallel to the hydrochloric acid metering tank, and an electromagnetic flow meter is installed at the inlet of the metering tank. The hydrochloric acid metering tank is equipped with high and low liquid levels. During normal operation, the metering pump works and is controlled by the liquid level of the hydrochloric acid storage tank (low level stops) and the liquid level of the hydrochloric acid metering tank (low level starts, high level stops), and is also controlled by the electromagnetic flow meter (the flow rate value can be set). In operation, as long as one of the conditions is met (reaching the set flow rate value of the electromagnetic flow meter or reaching the high liquid level of the hydrochloric acid metering tank), the metering pump stops working. ④ Hydrofluoric acid storage tank control: The hydrofluoric acid storage tank is equipped with a magnetic float level gauge (high, medium and low switch signals). Under normal operation, when the liquid level reaches the middle level, an alarm will sound to remind you to replenish hydrofluoric acid. The acid replenishment is manually controlled by a pneumatic diaphragm pump. ⑤ Hydrofluoric acid metering system control: A metering pump (120L / H) is installed at the outlet of the hydrofluoric acid storage tank. The outlet of the metering pump enters the hydrofluoric acid metering tank, and an electromagnetic flow meter is installed at the inlet of the metering tank. The hydrofluoric acid metering tank is equipped with high and low liquid levels. During normal operation, the metering pump works, controlled by the liquid level of the hydrofluoric acid storage tank (low level stops) and the liquid level of the hydrofluoric acid metering tank (low level starts, high level stops), and is also controlled by the electromagnetic flow meter (the flow rate value can be set). During operation, the metering pump stops working as long as one of the conditions is met (reaching the set flow rate value of the electromagnetic flow meter or reaching the high liquid level of the hydrofluoric acid metering tank). ⑥ Control of the acid dilution mixing tank: An acid dilution mixing tank is installed. The pure water inlet of the tank is equipped with a pneumatic valve and an electromagnetic flow meter. A magnetic level gauge (high and low switching signals) is installed on the tank body. During normal startup, when the magnetic level gauge detects that the water level in the tank is low, the inlet pneumatic valve is activated, controlled by the magnetic level gauge (low-level opening, high-level stopping), and simultaneously controlled by the electromagnetic flow meter (flow rate can be set). During operation, as long as one of the conditions is met (reaching the set flow rate value of the electromagnetic flow meter or reaching the high level of the acid dilution mixing tank), the pure water inlet pneumatic valve closes. ⑦ Acid dilution mixing tank stirring and discharge control: After the pure water inlet pneumatic valve of the acid dilution mixing tank is closed, start the mixer and simultaneously open the outlet pneumatic valves of the hydrochloric acid metering tank and the hydrofluoric acid metering tank; the mixer stops running after the set time (the time value can be set); when the hydrochloric acid metering tank and the hydrofluoric acid metering tank reach the low liquid level, close the corresponding outlet pneumatic valve; an acid dilution discharge pump is installed at the outlet of the acid dilution mixing tank, and the pump outlet is split into two pipelines to the two pickling mixing tanks respectively. An electromagnetic flow meter is installed on the main pipeline, and a pneumatic valve is installed at the dilution acid inlet of each pickling mixing tank; during normal operation, the No. 1 pickling mixing tank is run first, and then the No. 2 pickling mixing tank is run; S2 multi-stage closed pickling: ① Liquid inlet control for pickling tank No. 1 / No. 2: Each pickling tank is equipped with a pressure level gauge (high, medium, and low switching signals) and a mixer. During normal operation, when the liquid level in pickling tank No. 1 is low, the pneumatic valve at the dilution acid inlet on the tank body opens, and the acid dilution pump starts. When the pump reaches the set flow rate or the liquid level in pickling tank No. 1 is high, the acid dilution outlet pump is shut off, and the pneumatic valve at the dilution acid inlet of pickling tank No. 1 is also closed. The acid dilution pump is also controlled by the liquid level of the acid dilution mixing tank (low level stop). ② Weighing and unloading conveyor control: The No. 1 pickling mixing tank and the No. 2 pickling mixing tank share a set of weighing and unloading conveyors, which operate in both forward and reverse directions to transport materials to the pickling mixing tanks respectively; the closing signal of the pneumatic valve at the inlet of the diluted acid in the mixing tank is provided to the unloading conveyor, and feedback signals are received; during normal operation, when the No. 1 pickling mixing tank reaches the water inlet volume, the pneumatic valve at the inlet of the diluted acid is closed, and the unloading conveyor is started. After the conveyor finishes unloading, the signal is fed back to the cleaning process system, and the inlet pneumatic valve of the No. 2 pickling mixing tank is opened (at the same time, the No. 2 pickling mixing tank must meet the low liquid level signal requirements). When the set water inlet volume is reached, the pneumatic valve at the inlet of the diluted acid in the No. 2 pickling mixing tank is closed, and the unloading conveyor is started. After the conveyor finishes unloading, the operation is repeated again; ③ Interlocking control of pickling tank agitator: The agitator on pickling tank No. 1 / No. 2 is linked with the corresponding tank pressure level gauge (open at mid-range, stop at low-range, pressure value can be set). ④ Delayed operation of pickling mixing tank and linkage with centrifuge: After each unloading conveyor stops, pickling mixing tank No. 1 or pickling mixing tank No. 2 runs for a set time (the delay time is set, and the time value can be set. This time is the running time of pickling mixing tank No. 1 / pickling mixing tank No. 2), and then the signal is transmitted to centrifuge No. 1, and the centrifuge starts. ⑤ Pickling tank cleaning control: Each of the No. 1 and No. 2 pickling tanks is equipped with a cleaning pneumatic valve at the cleaning liquid inlet and a separate tank cleaning water pump (pure water from the pure water storage tank for cleaning); it can be manually controlled separately (time-controlled cleaning, the time value can be set). In automatic mode, after turning on the cleaning power of the No. 1 or No. 2 pickling tank, the corresponding cleaning pneumatic valve will be opened automatically. After the set time is reached, the water pump will be stopped and the cleaning pneumatic valve will be closed automatically. ⑥ Pickling Mixing Tank Pipeline Cleaning Control: Each of the No. 1 and No. 2 pickling mixing tanks is equipped with a cleaning inlet pneumatic valve at the outlet pump inlet, and a separate pipeline cleaning water pump (using pure water from a pure water storage tank for cleaning). During normal operation, when the outlet pump of either the No. 1 or No. 2 pickling mixing tank stops working (excluding fault factors), the corresponding cleaning inlet valve will automatically open (time-controlled cleaning, the time value can be set), the pipeline cleaning water pump will start, and after the set time is reached, the pump will automatically stop and the cleaning pneumatic valve will close. ⑦ Centrifuge No. 1 liquid diversion control: The outlet of centrifuge No. 1 is divided into two pipelines, one to two waste acid mixing tanks and the other to the No. 1 water washing circulation mixing tank. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 1 acid washing mixing tank / No. 2 acid washing mixing tank is started, the inlet pneumatic valve of the No. 1 water washing circulation mixing tank is opened first, and the liquid separated by centrifuge No. 1 enters the No. 1 water washing circulation mixing tank. S3 Multi-stage Continuous Countercurrent Water Wash: Primary water washing circulation and water washing unit: ① Circulation control of No. 1 water washing circulating mixing tank: A No. 1 water washing circulating mixing tank is installed, equipped with a pressure-type level gauge (high, medium, and low switching signals); a No. 1 water washing circulating mixing tank outlet pump is installed at the tank outlet, drawing water to the No. 1 centrifuge; in automatic operation, when the outlet pumps of No. 1 acid washing mixing tank / No. 2 acid washing mixing tank are shut off (at this time, all the liquid separated by the No. 1 centrifuge enters the No. 1 water washing circulating mixing tank), the No. 1 water washing circulating mixing tank outlet pump is started, and the liquid in the tank passes through the No. 1 centrifuge and re-enters the No. 1 water washing circulating mixing tank; the circulation runs for a period of time, which is time-controlled (the time value can be set). ② Control of the agitator in the No. 1 water washing circulating mixing tank: The No. 1 water washing circulating mixing tank is equipped with an agitator, which starts when the liquid level in the tank is detected; when the water pump of the No. 1 water washing circulating mixing tank stops, the agitator also stops running. ③ Control of liquid outlet switching for No. 1 water washing circulating mixing tank: After the water pump of No. 1 water washing circulating mixing tank runs for a set time, close the inlet pneumatic valve on the tank body; open the pneumatic valve on the pipeline from the outlet of No. 1 centrifuge to the two waste acid mixing tanks (in normal operation, No. 1 waste acid mixing tank runs first, then No. 2 waste acid mixing tank runs); when a low liquid level is detected in No. 1 water washing circulating mixing tank (a delay time is set, the time value can be set), stop the water pump of No. 1 water washing circulating mixing tank; (at this time, all the liquid separated by No. 1 centrifuge enters No. 1 waste acid mixing tank). ④ Control of drying and material conveying of centrifuge No. 1: After the water pump of the No. 1 water washing circulating mixing tank stops, the signal is transmitted to centrifuge No. 1. Under the action of centrifugal force, the centrifuge separates the solid particles in the slurry from the liquid. During this process, heating and drying are carried out (the centrifugal drying time is adjustable). After the centrifugal drying is completed, the material enters the No. 1 water washing mixing tank. ⑤ Liquid inlet control of No. 1 washing mixing tank: The pure water inlet of No. 1 washing mixing tank is equipped with a pneumatic valve and an electromagnetic flow meter, and the tank body is equipped with a pressure level gauge (high, medium and low switch signals); during normal start-up, after the No. 1 centrifuge stops working, the pure water inlet pneumatic valve is opened, and the inlet pneumatic valve is closed when the flow rate detected by the inlet electromagnetic flow meter reaches the set value (the flow rate value can be set) or reaches the high liquid level of No. 1 washing tank; ⑥ Interlocking control of the agitator in the No. 1 washing mixing tank: The agitator in the No. 1 washing mixing tank is linked with the corresponding pressure level gauge of the mixing tank (open at mid-range, stop at low-range, pressure value can be set). ⑦ Delayed operation of No. 1 water washing mixing tank and linkage with No. 2 centrifuge: After each stop of No. 1 centrifuge, No. 1 water washing mixing tank runs for a set time (the delay time is set, and the time value can be set. This time is set to the running time of No. 1 water washing mixing tank), and then the signal is transmitted to No. 2 centrifuge, and the centrifuge starts. Secondary water washing circulation and water washing unit: ① Centrifuge No. 2 liquid diversion control: The outlet of centrifuge No. 2 is divided into two pipelines, one to two turbid water mixing tanks and the other to the No. 2 water washing circulation mixing tank. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 1 water washing circulation mixing tank is started, the inlet pneumatic valve of the No. 2 water washing circulation mixing tank is opened first, and the liquid separated by centrifuge No. 2 enters the No. 2 water washing circulation mixing tank. ② Circulation control of the No. 2 water washing circulating mixing tank: A No. 2 water washing circulating mixing tank is installed, with a pressure-type liquid level gauge (high, medium, and low switching signals) on the tank body; a No. 2 water washing circulating mixing tank outlet is installed at the tank body outlet, pumping the liquid to the No. 2 centrifuge; in automatic operation, when the outlet pump of the No. 1 water washing mixing tank is turned off (at this time, all the liquid separated by the No. 2 centrifuge enters the No. 2 water washing circulating mixing tank), the outlet pump of the No. 2 water washing circulating mixing tank is started, and the liquid in the tank enters the No. 2 water washing circulating mixing tank again after passing through the No. 2 centrifuge; the circulation runs for a period of time, which is controlled by time (the time value can be set). ③ Control of the agitator in the No. 2 water washing circulating mixing tank: The No. 2 water washing circulating mixing tank is equipped with an agitator, which starts when the liquid level in the tank is detected; when the water pump of the No. 2 water washing circulating mixing tank stops, the agitator also stops running. ④ Control of liquid outlet switching in No. 2 water washing circulating mixing tank: After the water pump of No. 2 water washing circulating mixing tank runs for a set time, close the inlet pneumatic valve on the tank body; open the pneumatic valve on the pipeline from the outlet of No. 2 centrifuge to the two turbid water mixing tanks (in normal operation, No. 1 turbid water mixing tank runs first, then No. 2 turbid water mixing tank runs); when a low liquid level is detected in No. 2 water washing circulating mixing tank (a delay time is set, the time value can be set), stop the water pump of No. 2 water washing circulating mixing tank; (at this time, all the liquid separated by No. 2 centrifuge enters the turbid water mixing tank). ⑤ Drying and material conveying control of centrifuge No. 2: After the water pump of the No. 2 water washing circulating mixing tank stops, the signal is transmitted to centrifuge No. 2. Under the action of centrifugal force, the centrifuge separates the solid particles in the slurry from the liquid. During this process, heating and drying are carried out (the centrifugal drying time is adjustable). After drying, the material enters the No. 2 water washing mixing tank. ⑥ Liquid inlet control of No. 2 washing mixing tank: The pure water inlet of No. 2 washing mixing tank is equipped with a pneumatic valve and an electromagnetic flow meter, and a pressure level gauge (high, medium and low switching signals) is installed on the tank body; during normal start-up, after the No. 2 centrifuge stops working, the pure water inlet pneumatic valve is opened, and the inlet pneumatic valve is closed when the flow rate detected by the inlet electromagnetic flow meter reaches the set value (the flow rate value can be set) or reaches the high liquid level of No. 2 washing tank; ⑦ Interlocking control of the agitator in the No. 2 washing mixing tank: The agitator in the No. 2 washing mixing tank is linked with the corresponding pressure level gauge of the mixing tank (open at mid-range, stop at low-range, pressure value can be set). ⑧ The No. 2 water washing mixing tank operates with the No. 3 centrifuge in a time-delayed manner: After the No. 2 centrifuge stops each time, the No. 2 water washing mixing tank runs for a set time (the time delay is set and the time value can be set; this time is the running time of the No. 2 water washing mixing tank) and then the signal is transmitted to the No. 3 centrifuge, which then starts. Three-stage water washing circulation and water washing unit: ① Centrifuge No. 3 liquid diversion control: The outlet of centrifuge No. 3 is divided into two pipelines, one to two turbid water mixing tanks and the other to the No. 3 water washing circulation mixing tank. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 2 water washing circulation mixing tank is started, the inlet pneumatic valve of the No. 3 water washing circulation mixing tank is opened first, and the liquid separated by centrifuge No. 3 enters the No. 3 water washing circulation mixing tank. ② Circulation control of the No. 3 water washing circulating mixing tank: A No. 3 water washing circulating mixing tank is installed, equipped with a pressure level gauge (high, medium, and low voltage switching signals); a No. 3 water washing circulating mixing tank outlet pump is installed at the tank outlet, drawing water to the No. 3 centrifuge; in automatic operation, when the outlet pump of the No. 2 water washing mixing tank is shut off (at this time, all the liquid separated by the No. 3 centrifuge enters the No. 3 water washing circulating mixing tank), the No. 3 water washing circulating mixing tank outlet pump is started, and the liquid in the tank passes through the No. 3 centrifuge and re-enters the No. 3 water washing circulating mixing tank; the circulation runs for a period of time, which is time-controlled (the time value can be set). ③ Control of the agitator in the No. 3 water washing circulating mixing tank: The No. 3 water washing circulating mixing tank is equipped with an agitator, which starts when the liquid level in the tank is detected; the agitator also stops running when the water pump of the No. 3 water washing circulating mixing tank stops. ④ Liquid discharge switching control of No. 3 water washing circulating mixing tank: After the water pump of No. 3 water washing circulating mixing tank runs for a set time, close the inlet pneumatic valve on the tank body; open the pneumatic valve on the pipeline from the outlet of No. 3 centrifuge to the two turbid water mixing tanks (in normal operation, No. 1 turbid water mixing tank runs first, then No. 2 turbid water mixing tank runs); when a low liquid level is detected in No. 3 water washing circulating mixing tank (a delay running time is set, the time value can be set), stop the water pump of No. 3 water washing circulating mixing tank; (at this time, all the liquid separated by No. 3 centrifuge enters the turbid water mixing tank). ⑤ Drying and material conveying control of centrifuge No. 3: After the water pump of the No. 3 water washing circulating mixing tank stops, the signal is transmitted to centrifuge No. 3. Under the action of centrifugal force, the centrifuge separates the solid particles in the slurry from the liquid. During this process, heating and drying are carried out (the centrifugal drying time is adjustable). After drying, the material enters the No. 3 water washing mixing tank. ⑥ Liquid inlet control of No. 3 washing mixing tank: The pure water inlet of No. 3 washing mixing tank is equipped with a pneumatic valve and an electromagnetic flow meter, and a pressure level gauge (high, medium and low switch signals) is installed on the tank body; during normal start-up, after the No. 3 centrifuge stops working, the pure water inlet pneumatic valve is opened, and the inlet pneumatic valve is closed when the flow rate detected by the inlet electromagnetic flow meter reaches the set value (the flow rate value can be set) or reaches the high liquid level of No. 3 washing tank; ⑦ Interlocking control of the agitator in the No. 3 washing mixing tank: The agitator in the No. 3 washing mixing tank is linked with the corresponding pressure level gauge of the mixing tank (open at mid-range, stop at low-range, pressure value can be set). ⑧ The No. 3 water washing mixing tank is linked with the No. 4 centrifuge after the No. 3 centrifuge stops. After the No. 3 water washing mixing tank runs for a set time (the time delay is set and the time value can be set. This time is the running time of the No. 3 water washing mixing tank), the signal is transmitted to the No. 4 centrifuge and the centrifuge starts. Four-stage water washing circulation and discharge unit: ① Centrifuge No. 4 liquid diversion control: The outlet of centrifuge No. 4 is divided into two pipelines, one to two turbid water mixing tanks and the other to the No. 4 water washing circulation mixing tank. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 3 water washing circulation mixing tank is started, the inlet pneumatic valve of the No. 4 water washing circulation mixing tank is opened first, and the liquid separated by centrifuge No. 4 enters the No. 4 water washing circulation mixing tank. ② Circulation control of the No. 4 water washing circulating mixing tank: A No. 4 water washing circulating mixing tank is installed, with a pressure-type liquid level gauge (high, medium, and low switching signals) on the tank body; a No. 4 water washing circulating mixing tank outlet is installed at the tank body outlet, pumping the liquid to the No. 4 centrifuge; in automatic operation, when the outlet pump of the No. 3 water washing mixing tank is turned off (at this time, all the liquid separated by the No. 4 centrifuge enters the No. 4 water washing circulating mixing tank), the No. 4 water washing circulating mixing tank outlet pump is started, and the liquid in the tank enters the No. 4 water washing circulating mixing tank again after passing through the No. 4 centrifuge; the circulation runs for a period of time, which is controlled by time (the time value can be set). ③ Control of the agitator in the No. 4 water washing circulating mixing tank: The No. 4 water washing circulating mixing tank is equipped with an agitator, which starts when the liquid level in the tank is detected; when the water pump of the No. 4 water washing circulating mixing tank stops, the agitator also stops running. ④ Liquid discharge switching control of No. 4 water washing circulating mixing tank: After the water pump of No. 4 water washing circulating mixing tank runs for the set time, close the inlet pneumatic valve on the tank body; open the pneumatic valve on the pipeline from the outlet of No. 4 centrifuge to the two turbid water mixing tanks (in normal operation, No. 1 turbid water mixing tank runs first, then No. 2 turbid water mixing tank runs); when a low liquid level is detected in No. 4 water washing circulating mixing tank (a delay running time is set, the time value can be set), stop the water pump of No. 4 water washing circulating mixing tank; (at this time, all the liquid separated by No. 4 centrifuge enters the turbid water mixing tank). ⑤ Drying and discharge control of centrifuge No. 4: After the water pump of the No. 4 water washing circulating mixing tank stops, the signal is transmitted to centrifuge No. 4. Under the action of centrifugal force, the centrifuge separates the solid particles in the slurry from the liquid. During this process, heating and drying are carried out (centrifugal drying time is adjustable). After drying, the material enters the equipment of the next process. ⑥ Process linkage control of centrifuge No. 4: The operation signal of centrifuge No. 4 is fed back to the equipment in the next process to ensure the continuity of the process line; S4 acid recovery treatment: ① Waste acid mixing tank inlet control: The outlet of centrifuge No. 1 is connected to two waste acid mixing tanks. Pneumatic valves are installed at the inlet of each tank. Magnetic level gauges (high and low switch signals) are installed on each waste acid mixing tank. During normal operation, waste acid mixing tank No. 1 is started first, followed by waste acid mixing tank No. 2. When the liquid level in waste acid mixing tank No. 1 reaches the high level, the pneumatic valve for water inlet of waste acid mixing tank No. 1 is closed, while the pneumatic valve for water inlet of waste acid mixing tank No. 2 is opened. ② Linkage control of the No. 1 ceramic membrane equipment: The level signals of the magnetic flip plates on the two waste acid mixing tanks are transmitted to the No. 1 ceramic membrane equipment respectively; the waste acid booster pump and the two concentrate booster pumps are controlled by the No. 1 ceramic membrane equipment; during normal operation, regardless of which waste acid tank has a high level, the corresponding outlet pneumatic valve opens, and the operation signal is fed back to the ceramic membrane equipment; at this time, the ceramic membrane starts to work and controls the operation of the waste acid booster pump. When the ceramic membrane circulates until the concentrate reaches the required level, the waste acid booster pump is turned off, and the pneumatic valves before and after the corresponding concentrate booster pump and water pump are opened. ③ Control of the No. 1 50% concentrated acid solution mixing tank: The concentrated solution is pumped to the No. 1 50% concentrated acid solution mixing tank. The No. 1 50% concentrated acid solution mixing tank is equipped with a magnetic float level gauge (high, medium, and low switching signals). The signal is transmitted to the No. 1 centrifuge (medium start, low stop) and simultaneously to the two concentrated solution pumps (low start, high stop). The No. 1 centrifuge controls the operation of the concentrated acid solution pumps. During normal operation, when the liquid level in the No. 1 50% concentrated acid solution mixing tank reaches the specified level, the operation signal is transmitted to the No. 1 centrifuge, and the centrifuge is in operation, the 50% concentrated acid solution pump can only be started. Under normal circumstances, the 50% concentrated acid solution pump cannot operate independently. First, the liquid level condition in the No. 1 50% concentrated acid solution mixing tank must be met. Second, the 50% concentrated acid solution pump can only be started when the water pumps of the No. 1 or No. 2 pickling mixing tank are working. ④ Acid recovery storage tank control: The clear liquid outlet of the No. 1 ceramic membrane equipment is connected to the acid recovery storage tank. The tank is equipped with a magnetic level gauge (high, medium and low switching signals). During normal operation, when the medium level condition is met, the signal is transmitted to the waste acid recovery device to start operation and the acid regeneration booster pump is started at the same time. When the acid recovery storage tank is at a low level, the acid regeneration booster pump stops. ⑤ Waste acid recovery device diversion control: The waste acid recovery device has two pipelines for water discharge. One pipeline separates the recyclable acid into the recovery acid tank, and the other pipeline separates the non-recyclable acid into the acid treatment raw water tank. Each tank is equipped with a magnetic float level gauge (high, medium and low switch signals). When either tank reaches the high level, the waste acid recovery device stops running, and the front-end acid regeneration booster pump also stops. ⑥ Recirculation control of the acid recovery tank: The acid recovery tank is equipped with a magnetic level gauge (high, medium, and low switching signals), and a acid recovery booster pump is installed. The pump outlet pipeline is connected to the acid dilution and mixing tank. The level control is controlled by the level of the acid recovery tank (medium level on, low level off) and also by the level control of the acid dilution and mixing tank (low level on, high level off). ⑦ Acid treatment raw water tank linkage control: The acid treatment raw water tank is equipped with a magnetic float level gauge (high, medium and low switch signals). The signal is transmitted to the waste acid recovery device (low start, high stop) and simultaneously to the subsequent acid treatment equipment (medium start, low stop) to ensure the continuity of the process line. S5 washing and turbid water treatment: ① Turbid water tank inlet control: The centrifuge outlets of washing mixing tanks No. 1, No. 2, No. 3, and No. 4 are connected in parallel and each inlet is fed into two turbid water tanks. Pneumatic valves are installed at the inlet of each tank, and magnetic level gauges (high and low switching signals) are installed on each tank. During normal operation, No. 1 turbid water mixing tank is started first, followed by No. 2 turbid water mixing tank. When the liquid level in No. 1 turbid water mixing tank reaches the high level, the inlet pneumatic valve of No. 1 turbid water mixing tank is closed, while the inlet pneumatic valve of No. 2 turbid water mixing tank is opened. ② Interlocking control of the No. 2 ceramic membrane equipment: The liquid level signals of the magnetic flip plates on the two turbid water tanks are transmitted to the No. 2 ceramic membrane equipment respectively; the turbid water tank lift pump and the concentrate outlet pumps of the two turbid water tanks are controlled by the No. 2 ceramic membrane equipment; during normal operation, regardless of which turbid water tank has a high liquid level, the corresponding outlet pneumatic valve opens, and the operation signal is fed back to the ceramic membrane equipment; at this time, the ceramic membrane starts to work and controls the operation of the turbid water tank lift pump. When the ceramic membrane circulates until the concentrate reaches the required level, the turbid water tank lift pump closes, and the concentrate outlet pump of the corresponding tank and the pneumatic valves before and after the pump are opened; ③ Control of unqualified water return from turbid water tank: The turbid water tank is equipped with an unqualified water lift pump, and the pipeline outlet is split into two pipelines to two pickling mixing tanks respectively. Pneumatic valves are installed on both pipelines. When the sampling detects that the solution in the tank is not up to standard or the membrane treatment equipment is abnormal, the valves and water pumps are manually opened. S6 concentrate circulation: The concentrated liquid from the turbid water tank is pumped to the No. 2 50% concentrated acid solution mixing tank. The No. 2 50% concentrated acid solution mixing tank is equipped with a magnetic level gauge (high, medium, and low switching signals). The signal is transmitted to the No. 2 centrifuge (medium-level start, low-level stop) and simultaneously to the two turbid water tank concentrated liquid outlet pumps (low-level start, high-level stop). The No. 2 centrifuge controls the operation of the 50% concentrated acid solution booster pump. During normal operation, when the liquid level in the No. 2 50% concentrated acid solution mixing tank reaches the specified level, the operation signal is transmitted to the No. 2 centrifuge, and the centrifuge is running, the 50% concentrated acid solution booster pump can only be started. Under normal circumstances, the 50% concentrated acid solution booster pump cannot operate independently. First, the liquid level condition in the No. 2 50% concentrated acid solution mixing tank must be met. Second, the No. 1 water washing mixing tank outlet pump can only be started when the 50% concentrated acid solution booster pump is working, pumping the 50% concentrated acid solution to the centrifuge for separation. The separated acid solution is then piped back to the acid washing unit for reuse.

[0022] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a multi-stage continuous washing structure, which brings the mixture of fresh washing water and acid solution into contact with silicon nitride powder containing impurities. This rapidly dissolves and removes the metal impurity ions (Fe3+, Al3+, Ca2+) from the powder particles. Subsequently, fresh washing water is used in a multi-stage continuous manner to gradually dilute and remove the acid radical ions (Cl-, SO42-, F-) between the powder particles and within the aggregates. This solves the problems of insufficient mass transfer driving force and incomplete washing in the intermittent washing of the prior art.

[0023] 2. This invention, by setting up an acid solution classification collection and gradient recycling system, classifies and collects acid solutions of different reaction stages and different impurity concentrations. High-concentration acid solutions are returned to the acid washing reaction unit to continue participating in the impurity dissolution reaction, while low-concentration acid solutions are discharged after treatment. This avoids the acid waste and powder pollution caused by the mixed discharge or simple reuse of acid solutions in existing technologies. At the same time, the multi-stage washing design, compared with existing traditional washing methods, can significantly reduce the amount of fresh water used and the amount of wastewater generated while achieving the same washing effect. It also improves the utilization rate of acid solutions and water resources, reduces the acid consumption per unit weight of silicon nitride powder, significantly reduces the enterprise's production and operation costs and environmental governance pressure, and conforms to the industrial policy of energy conservation and emission reduction.

[0024] 3. This invention optimizes the internal mass transfer structure of the reactor, avoiding the problems of slurry short-circuiting, backmixing, and local accumulation in existing continuous pickling lines. This ensures that silicon nitride powder and acid solution are fully contacted and uniformly mixed, guaranteeing a consistent residence time for each powder particle (residence time fluctuation ≤5%). This improves the dissolution reaction rate of impurities (metal oxides, free silicon, oxide layer) and shortens the overall processing cycle. At the same time, the continuous closed-loop operation design eliminates the waiting time for intermittent unloading and feeding in existing technologies, realizing integrated continuous operation of pickling, washing, solid-liquid separation, and acid mist treatment. This meets the needs of large-scale and continuous production and enhances the enterprise's production capacity competitiveness.

[0025] 4. This invention employs a fully enclosed design, with the pickling reactor, washing unit, solid-liquid separation equipment, and pipelines all using sealed structures. It is equipped with a centralized acid mist collection and adsorption treatment system to collect and treat all acid mist (such as HF mist and HCl mist) volatilized during the pickling process, preventing the unorganized dispersion of acid mist. At the same time, the parts of the equipment that come into contact with the medium are made of corrosion-resistant materials (such as PTFE and Hastelloy) to reduce the corrosion of the equipment by the acid and extend the service life of the equipment.

[0026] 5. This invention, by configuring an online detection system and a closed-loop automatic control system, monitors in real time the acid concentration, temperature, and slurry flow rate of the pickling reaction unit, the pH value and conductivity of the washing unit, and the solid-liquid ratio of the solid-liquid separation unit. The control system automatically adjusts various parameters (such as acid supply, washing water flow rate, and reaction temperature) to achieve precise control of the pickling and washing processes, solving the problems of large errors and unstable parameters in existing technologies, and further reducing production costs and quality losses.

[0027] 6. This invention not only specifically solves all the core technical problems of traditional silicon nitride powder pickling lines, but also achieves multiple technical effects such as "quality improvement, efficiency enhancement, cost reduction, environmental protection, and safety." Compared with existing technologies, it has achieved breakthrough improvements in product quality, production efficiency, cost control, and safety and environmental protection. From an industrial application perspective, the pickling line of this application can be widely used in the large-scale production of high-purity silicon nitride powder, promoting the application of silicon nitride powder in high-end equipment, semiconductors, new energy, and other fields. It has significant economic value, environmental value, and industrial promotion value, and has outstanding substantive features and significant progress compared with existing technologies. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the pickling unit structure of the present invention; Figure 3 This is a schematic diagram of the acid recovery unit structure of the present invention; Figure 4This is a schematic diagram of the turbid water treatment unit structure of the present invention; Figure 5 This is a schematic diagram of the multi-stage water washing unit structure of the present invention; Figure 6 This is a schematic diagram of the concentrated liquid treatment unit structure of the present invention; Figure 7 This is a schematic diagram of the hydrochloric acid storage tank structure of the present invention; Figure 8 This is a schematic diagram of the hydrofluoric acid storage tank structure of the present invention; Figure 9 This is a schematic diagram of the acid dilution mixing and stirring tank structure of the present invention; Figure 10 This is a schematic diagram of the waste acid mixing tank structure of the present invention; Figure 11 This is a schematic diagram of the water washing mixing tank structure of the present invention; Figure 12 This is a schematic diagram of the structure of the turbid water mixing tank of the present invention; Figure 13 This is a schematic diagram of the 50% waste acid solution stirring tank structure of the present invention; Figure 14 This is a schematic diagram of the water washing circulating mixing tank structure of the present invention; Figure 15 This is a schematic diagram of the ceramic membrane forward washing water tank structure of the present invention; Figure 16 This is a schematic diagram of the water purification tank structure of the present invention; Figure 17 This is a schematic diagram of the hydrochloric acid metering tank structure of the present invention; Figure 18 This is a schematic diagram of the hydrofluoric acid metering tank structure of the present invention; Figure 19 This is a schematic diagram of the pure water storage tank structure of the present invention; In the diagram: 1. Pure water storage tank; 2. Tank cleaning pump; 3. Pipeline cleaning pump; 4. Pump outlet for pickling mixing tank No. 1; 5. Pickling mixing tank No. 1; 6. Pickling mixing tank No. 2; 7. Pump outlet for pickling mixing tank No. 2; 8. Pump outlet for pure water storage tank; 9. Pump outlet for acid dilution tank; 10. Acid dilution mixing tank; 11. Hydrofluoric acid booster pump; 12. Hydrofluoric acid storage tank; 13. Hydrofluoric acid metering pump No. 1; 14. Hydrofluoric acid metering tank; 15. Hydrochloric acid booster pump; 16. Hydrochloric acid storage tank; 17. Hydrochloric acid metering pump No. 1; 18. Hydrochloric acid metering tank; 19. 20. Acid recovery tank; 21. Acid recovery booster pump; 22. Acid treatment booster pump; 23. Acid treatment raw water tank; 24. Acid recovery equipment; 25. Acid regeneration booster pump; 26. Acid recovery storage water tank; 27. No. 1 50% concentrated acid mixing tank; 28. No. 1 50% concentrated acid booster pump; 29. ​​No. 2 centrifuge; 30. No. 3 centrifuge; 31. No. 4 centrifuge; 32. No. 1 water washing circulating mixing tank; 33. No. 1 water washing circulating mixing tank outlet pump; 34. No. 1 water washing mixing tank; 35. No. 1 water washing mixing tank. 36. No. 2 Water Washing Circulating Mixing Tank; 37. No. 2 Water Washing Circulating Mixing Tank Outlet Pump; 38. No. 2 Water Washing Mixing Tank; 39. No. 2 Water Washing Mixing Tank Outlet Pump; 40. No. 3 Water Washing Circulating Mixing Tank; 41. No. 3 Water Washing Circulating Mixing Tank Outlet Pump; 42. No. 3 Water Washing Mixing Tank; 43. No. 3 Water Washing Mixing Tank Outlet Pump; 44. No. 4 Water Washing Circulating Mixing Tank; 45. No. 4 Water Washing Circulating Mixing Tank Outlet Pump; 46. Mixing Tank Rinse Water Outlet Pump; 47. No. 1 Ceramic Membrane Forward Washing Water Tank; 48. Waste Acid Lifting Pump; 49. No. 1 Ceramic Membrane Equipment; 50. Waste acid mixing tank No. 1; 51. Concentrate booster pump No. 1; 52. Concentrate booster pump No. 2; 53. Waste acid mixing tank No. 2; 54. Clean water booster pump; 55. Unqualified booster pump for turbid water tank; 56. Clean water tank; 57. Ceramic membrane forward wash water tank No. 2; 58. Ceramic membrane equipment No. 2; 59. Turbid water booster pump; 60. Turbid water mixing tank No. 1; 61. Concentrate outlet pump for turbid water tank No. 1; 62. Concentrate outlet pump for turbid water tank No. 2; 63. Turbid water mixing tank No. 2; 64. 50% concentrated acid mixing tank No. 2; 65. 50% concentrated acid booster pump No. 2. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1 Please see Figure 1-19The present invention provides the following technical solution: a closed-loop multi-stage washing silicon nitride powder pickling production line, the production line including a pickling unit, an acid recovery unit, a turbid water treatment unit, a multi-stage water washing unit, and a concentrated liquid treatment unit; The turbid water treatment unit includes a first turbid water mixing tank 60, a second turbid water mixing tank 63, a first ceramic membrane device 49, a second ceramic membrane device 58, and a clean water tank 56. The first turbid water mixing tank 60 and the second turbid water mixing tank 63 are respectively connected to the first ceramic membrane device 49 and the second ceramic membrane device 58 via a turbid water lift pump 59. The clean water outlets of the first ceramic membrane device 49 and the second ceramic membrane device 58 are both connected to the clean water tank 56 via a clean water lift pump 54. The first ceramic membrane forward wash water tank 47 and the second ceramic membrane forward wash water tank 57 are respectively connected to the first ceramic membrane device 49 and the second ceramic membrane device 58. The multi-stage washing unit includes a No. 1 washing mixing tank 34, a No. 2 washing mixing tank 38, a No. 3 washing mixing tank 42, a No. 4 washing mixing tank 44, a No. 3 centrifuge 30, and a No. 4 centrifuge 31. A pure water storage tank 1 is connected to the No. 1 washing circulating mixing tank 32, the No. 2 washing circulating mixing tank 36, the No. 3 washing circulating mixing tank 40, and the No. 4 washing circulating mixing tank 44 via a pure water storage tank outlet pump 8. The No. 1 washing circulating mixing tank 32 is connected to the No. 1 washing mixing tank 34 via a No. 1 washing circulating mixing tank outlet pump 33. The circulating mixing tank 36 is connected to the No. 2 washing mixing tank 38 via the No. 2 washing circulating mixing tank outlet pump 37. The No. 3 washing circulating mixing tank 40 is connected to the No. 3 washing mixing tank 42 via the No. 3 washing circulating mixing tank outlet pump 41. The No. 4 washing circulating mixing tank 44 is connected to the No. 4 washing mixing tank 44 via the No. 4 washing circulating mixing tank outlet pump 45. The outlets of the No. 1 washing mixing tank 34 and the No. 2 washing mixing tank 38 merge and are connected to the No. 3 centrifuge 30. The outlets of the No. 3 washing mixing tank 42 and the No. 4 washing mixing tank 44 merge and are connected to the No. 4 centrifuge 31. The concentrated liquid treatment unit includes a No. 1 waste acid mixing tank 50, a No. 2 waste acid mixing tank 53, a No. 1 50% concentrated acid mixing tank 26, and a No. 2 50% concentrated acid mixing tank 64. The concentrated liquid outlets of the No. 1 ceramic membrane equipment 49 and the No. 2 ceramic membrane equipment 58 are respectively connected to the No. 1 waste acid mixing tank 50 and the No. 2 waste acid mixing tank 53. The No. 1 waste acid mixing tank 50 is connected to the No. 1 50% concentrated acid mixing tank 26 and the No. 2 50% concentrated acid mixing tank 64 via the No. 1 concentrated acid lift pump 51 and the No. 2 waste acid mixing tank 53 via the No. 2 concentrated acid lift pump 52, respectively. The No. 1 50% concentrated acid mixing tank 26 is connected to the No. 1 50% concentrated acid lift pump 27 and the No. 2 50% concentrated acid mixing tank 64 via the No. 2 50% concentrated acid lift pump 65, respectively, and all are returned to the pickling unit. The outlet of the No. 2 50% concentrated acid lift pump 65 is connected to an external centrifuge. Pure water storage tank 1 is connected to the cleaning interfaces of each mixing tank and pipeline through tank cleaning pump 2, pipeline cleaning pump 3, and mixing tank flushing water outlet pump 46. Clean water tank 56 is returned to the turbid water treatment unit through turbid water tank unqualified lift pump 55. Control valves are installed at the outlets of all lift pumps, circulation pumps, outlet pumps, water tanks, mixing tanks and storage tanks.

[0031] Furthermore, in this invention, the outlet end of the acid treatment booster pump 21 is connected to an external non-recoverable acid treatment device.

[0032] Furthermore, in this invention, the pure water storage tank 1 is connected to an external reverse osmosis water outlet pipe.

[0033] Furthermore, in this invention, the inlet end of the water purification booster pump 54 is connected to the water supply pipeline of the radiator in the factory area, and the unqualified booster pump 55 for the turbid water tank is connected to the raw water tank for acid treatment.

[0034] Furthermore, in this invention, the discharge end of centrifuge No. 4 31 is connected to an external drying device.

[0035] Furthermore, in this invention, the first pickling mixing tank 5 and the second pickling mixing tank 6 of the pickling unit are connected in series in a closed structure, and the inner walls of the mixing tanks are made of corrosion-resistant material.

[0036] Furthermore, in this invention, the first ceramic membrane device 49 and the second ceramic membrane device 58 of the turbid water treatment unit are connected in parallel and have an online backwashing function.

[0037] Furthermore, in this invention, the multi-stage washing unit is a four-stage continuous countercurrent washing structure, and each stage of the washing mixing tank is equipped with an online conductivity and pH detection probe.

[0038] Furthermore, in this invention, centrifuge No. 1 28, centrifuge No. 29, centrifuge No. 30, and centrifuge No. 4 31 are all corrosion-resistant, sealed centrifuges.

[0039] Furthermore, the manufacturing process of this invention includes the following steps: S1 acid preparation and delivery unit: ① Control of hydrochloric acid storage tank 16: The hydrochloric acid storage tank 16 is equipped with a magnetic float level gauge (high, medium and low switch signals); under normal operation, when the liquid level reaches the medium level, an alarm will sound to remind the tank to replenish hydrochloric acid. The replenishment of acid is achieved by manually controlling the operation of the pneumatic diaphragm pump. ② Control of hydrochloric acid booster pump 15 / hydrofluoric acid booster pump 11: Hydrochloric acid booster pump 15 and hydrofluoric acid booster pump 11 (acid addition) are set up and are manually controlled separately; during normal operation, after hearing the alarm, open the inlet and outlet valves of the booster pump of the corresponding storage tank and start the water pump. After reaching the high liquid level, manually stop the water pump. ③ Hydrochloric acid metering system control: One (662L / H) metering pump is installed at the outlet of hydrochloric acid storage tank 16. The outlet pipeline of the metering pump is connected in parallel to hydrochloric acid metering tank 18, and an electromagnetic flow meter is installed at the inlet of the metering tank. The hydrochloric acid metering tank 18 is equipped with high and low liquid levels. During normal operation, the metering pump works and is controlled by the liquid level of hydrochloric acid storage tank 16 (low level stops) and by the liquid level of hydrochloric acid metering tank 18 (low level starts, high level stops), and is also controlled by the electromagnetic flow meter (the flow rate value can be set). In operation, as long as one of the conditions is met (reaching the set flow rate value of the electromagnetic flow meter or reaching the high liquid level of hydrochloric acid metering tank 18), the metering pump stops working. ④ Control of hydrofluoric acid storage tank 12: The hydrofluoric acid storage tank 12 is equipped with a magnetic float level gauge (high, medium and low switch signals). Under normal operation, when the liquid level reaches the middle level, an alarm will be sounded to remind the tank to replenish hydrofluoric acid. The acid replenishment is manually controlled by a pneumatic diaphragm pump. ⑤ Hydrofluoric acid metering system control: A metering pump (120L / H) is installed at the outlet of hydrofluoric acid storage tank 12. The outlet of the metering pump enters hydrofluoric acid metering tank 14, and an electromagnetic flow meter is installed at the inlet of the metering tank. The hydrofluoric acid metering tank 14 is equipped with high and low liquid levels. During normal operation, the metering pump works and is controlled by the liquid level of hydrofluoric acid storage tank 12 (low level stops) and by the liquid level of hydrofluoric acid metering tank 14 (low level starts, high level stops), and is also controlled by the electromagnetic flow meter (the flow rate value can be set). In operation, as long as one of the conditions is met (reaching the set flow rate value of the electromagnetic flow meter or reaching the high liquid level of hydrofluoric acid metering tank 14), the metering pump stops working. ⑥ Control of Acid Dilution Mixing Tank 10: An acid dilution mixing tank 10 is provided. The pure water inlet of the tank is equipped with a pneumatic valve and an electromagnetic flow meter. A magnetic level gauge (high and low switching signal) is installed on the tank body. During normal startup, when the magnetic level gauge detects that the water level in the tank is low, the inlet pneumatic valve is activated, controlled by the magnetic level gauge (low-level opening, high-level stopping), and simultaneously controlled by the electromagnetic flow meter (flow rate can be set). During operation, as long as one of the conditions is met (reaching the set flow rate value of the electromagnetic flow meter or reaching the high level of the acid dilution mixing tank 10), the pure water inlet pneumatic valve is closed. ⑦ Acid dilution mixing and stirring tank 10 stirring and liquid discharge control: After the pure water inlet pneumatic valve of acid dilution mixing and stirring tank 10 is closed, start the stirrer and simultaneously open the outlet pneumatic valves of hydrochloric acid metering tank 18 and hydrofluoric acid metering tank 14; the stirrer stops running after the set time (the time value can be set); when hydrochloric acid metering tank 18 and hydrofluoric acid metering tank 14 reach the low liquid level, close the corresponding outlet pneumatic valve; acid dilution mixing and stirring tank 10 is equipped with an acid dilution water discharge pump 9 at the outlet, and the pump outlet is divided into two pipelines to two pickling mixing tanks respectively. An electromagnetic flow meter is installed on the main pipeline, and a pneumatic valve is installed at the acid dilution inlet of each pickling mixing tank; during normal operation, pickling mixing tank 5 is run first, and then pickling mixing tank 6 is run; S2 multi-stage closed pickling: ① Liquid inlet control for pickling mixing tank 5 (No. 1) and pickling mixing tank 6 (No. 2): Each pickling mixing tank (No. 1) and pickling mixing tank 6 is equipped with a pressure level gauge (high, medium, and low switching signals) and a mixer. During normal operation, when the liquid level in pickling mixing tank 5 is low, the pneumatic valve at the dilution acid inlet on the tank body opens, and the acid dilution pump starts. When the pump reaches the set flow rate or the liquid level in pickling mixing tank 5 is high, the acid dilution outlet pump 9 is shut down, and the pneumatic valve at the dilution acid inlet of pickling tank 5 is also closed. The acid dilution pump is also controlled by the liquid level of the acid dilution mixing tank 10 (low level stop). ② Weighing and unloading conveyor control: Pickling tank 5 (No. 1) and pickling tank 6 (No. 2) share a single weighing and unloading conveyor, which operates in both forward and reverse directions to transport materials to the two pickling tanks respectively. The closing signals of the pneumatic valves at the inlet of the diluted acid solution in both tanks are provided to the unloading conveyor, and feedback signals are received. During normal operation, when pickling tank 5 reaches the water inlet volume, the pneumatic valve at the inlet of the diluted acid solution is closed, and the unloading conveyor is started. After the conveyor finishes unloading, a signal is fed back to the cleaning process system to open the pneumatic valve at the inlet of pickling tank 6 (at the same time, pickling tank 6 must meet the low liquid level signal requirements). When the set water inlet volume is reached, the pneumatic valve at the inlet of the diluted acid solution in pickling tank 6 is closed, and the unloading conveyor is started. After the conveyor finishes unloading, the process is repeated. ③ Interlocking control of pickling tank agitators: The agitators on pickling tank 5 of No. 1 and pickling tank 6 of No. 2 are linked with the corresponding tank pressure level gauges (open at mid-range, stop at low-range, pressure value can be set). ④ Delayed operation of pickling mixing tank and linkage with centrifuge: After each unloading conveyor stops, pickling mixing tank 5 or pickling mixing tank 6 runs for a set time (the delay time is set, and the time value can be set. This time is set to the running time of pickling mixing tank 5 / pickling mixing tank 6), and then the signal is transmitted to centrifuge 28, and the centrifuge starts. ⑤ Pickling tank cleaning control: The cleaning liquid inlet of pickling tank 5 (No. 1) and pickling tank 6 (No. 2) is equipped with a cleaning pneumatic valve and a separate tank cleaning water pump 2 (pure water from the pure water storage tank 1 for cleaning); it can be manually controlled separately (time-controlled cleaning, the time value can be set). In automatic mode, after turning on the cleaning power of pickling tank 5 (No. 1) or pickling tank 6 (No. 2), the corresponding cleaning pneumatic valve will be opened automatically. After the set time is reached, the water pump will be stopped and the cleaning pneumatic valve will be closed automatically. ⑥ Pickling tank pipeline cleaning control: A cleaning inlet pneumatic valve is installed at the water outlet pump inlet of pickling tank 5 (No. 1) and pickling tank 6 (No. 2), and a separate pipeline cleaning water pump 3 is installed (using pure water from the pure water storage tank 1 for cleaning); During normal operation, when the water outlet pump of pickling tank 5 (No. 1) or pickling tank 6 (No. 2) stops working (excluding fault factors), the corresponding cleaning inlet valve will be automatically opened (time-controlled cleaning, the time value can be set), the pipeline cleaning water pump 3 will be started, and the pump will be automatically stopped and the cleaning pneumatic valve will be closed after the set time is reached; ⑦ Centrifuge No. 1 28 liquid diversion control: The outlet of centrifuge No. 1 28 is divided into two pipelines, one to two waste acid mixing tanks, and the other to the No. 1 water washing circulation mixing tank 32. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 1 acid washing mixing tank 5 / No. 2 acid washing mixing tank 6 is started, the water inlet pneumatic valve of the No. 1 water washing circulation mixing tank 32 is opened first, and the liquid separated by centrifuge No. 1 28 enters the No. 1 water washing circulation mixing tank 32. S3 Multi-stage Continuous Countercurrent Water Wash: Primary water washing circulation and water washing unit: ① Circulation control of No. 1 water washing circulating mixing tank 32: One No. 1 water washing circulating mixing tank 32 is installed, and a pressure-type liquid level gauge (high, medium, and low switching signals) is installed on the tank body; one No. 1 water washing circulating mixing tank outlet pump 33 is installed at the tank body outlet, which pumps to No. 1 centrifuge 28; in automatic operation, when the outlet pump of No. 1 acid washing mixing tank 5 / No. 2 acid washing mixing tank 6 is turned off (at this time, all the liquid separated by No. 1 centrifuge 28 enters No. 1 water washing circulating mixing tank 32), the outlet pump of No. 1 water washing circulating mixing tank 33 is started, and the liquid in the tank enters No. 1 water washing circulating mixing tank 32 again after passing through No. 1 centrifuge 28; the circulation runs for a period of time, and this operation is controlled by time (the time value can be set). ② Control of the agitator in the No. 1 water washing circulating mixing tank 32: The No. 1 water washing circulating mixing tank 32 is equipped with one agitator, which starts when the liquid level in the tank is detected; when the No. 1 water washing circulating mixing tank outlet pump 33 stops, the agitator also stops running. ③ Liquid discharge switching control of No. 1 water washing circulating mixing tank 32: After the No. 1 water washing circulating mixing tank outlet pump 33 runs for a set time, the inlet pneumatic valve on the tank body is closed; the pneumatic valve on the pipeline from the outlet of No. 1 centrifuge 28 to the two waste acid mixing tanks is opened (during normal operation, No. 1 waste acid mixing tank 50 runs first, then No. 2 waste acid mixing tank 53 runs); when a low liquid level is detected in No. 1 water washing circulating mixing tank 32 (a delay running time is set, the time value can be set), the No. 1 water washing circulating mixing tank outlet pump 33 is stopped; (at this time, all the liquid separated by No. 1 centrifuge 28 enters No. 1 waste acid mixing tank 50). ④ Control of drying and material conveying of centrifuge 28: After the water pump 33 of the No. 1 washing and circulating mixing tank stops, the signal is transmitted to centrifuge 28. The centrifuge separates the solid particles and liquid in the slurry under the action of centrifugal force. During this process, heating and drying are carried out (the centrifugal drying time is adjustable). After the centrifugal drying is completed, the material enters the No. 1 washing and mixing tank 34. ⑤ Liquid inlet control of No. 1 washing mixing tank 34: The pure water inlet of No. 1 washing mixing tank 34 is equipped with a pneumatic valve and an electromagnetic flow meter, and the tank body is equipped with a pressure level gauge (high, medium and low switch signals); during normal start-up, after the No. 1 centrifuge 28 stops working, the pure water inlet pneumatic valve is opened. When the flow rate detected by the inlet electromagnetic flow meter reaches the set value (the flow rate value can be set) or reaches the high liquid level of No. 1 washing tank, the inlet pneumatic valve is closed. ⑥ Linkage control of mixer 34 in No. 1 water washing mixing tank: The mixer of No. 1 water washing mixing tank 34 is linked with the corresponding mixing tank pressure level gauge (open at mid-range, stop at low-range, pressure value can be set). ⑦ Delayed operation of No. 1 washing mixing tank 34 and linkage with No. 2 centrifuge 29: After each stop of No. 1 centrifuge 28, No. 1 washing mixing tank 34 runs for a set time (the delay time is set, and the time value can be set. This time is set to the running time of No. 1 washing mixing tank), and then the signal is transmitted to No. 2 centrifuge 29, and the centrifuge starts. Secondary water washing circulation and water washing unit: ① Liquid diversion control of centrifuge No. 29: The outlet of centrifuge No. 29 is divided into two pipelines, one to two turbid water mixing tanks and the other to the No. 2 water washing circulation mixing tank 36. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 1 water washing circulation mixing tank 32 is started, the inlet pneumatic valve of the No. 2 water washing circulation mixing tank 36 is opened first, and the liquid separated by centrifuge No. 29 enters the No. 2 water washing circulation mixing tank 36. ② Circulation control of No. 2 water washing circulating mixing tank 36: One No. 2 water washing circulating mixing tank 36 is installed, with a pressure level gauge (high, medium, and low switching signals) on the tank body; a No. 2 water washing circulating mixing tank outlet pump 37 is installed at the tank outlet, pumping the liquid to the No. 2 centrifuge 29; in automatic operation, when the outlet pump of the No. 1 water washing mixing tank 34 is turned off (at this time, all the liquid separated by the No. 2 centrifuge 29 enters the No. 2 water washing circulating mixing tank 36), the No. 2 water washing circulating mixing tank outlet pump 37 is started, and the liquid in the tank enters the No. 2 water washing circulating mixing tank 36 again after passing through the No. 2 centrifuge 29; the circulation runs for a period of time, which is controlled by time (the time value can be set). ③ Control of the agitator in the No. 2 water washing circulating mixing tank 36: The No. 2 water washing circulating mixing tank 36 is equipped with one agitator, which starts when the liquid level in the tank is detected; when the No. 2 water washing circulating mixing tank outlet pump 37 stops, the agitator also stops running. ④ Liquid outlet switching control of No. 2 water washing circulating mixing tank 36: After the No. 2 water washing circulating mixing tank outlet pump 37 runs for the set time, the inlet pneumatic valve on the tank body is closed; the pneumatic valve on the pipeline from the outlet of No. 2 centrifuge 29 to the two turbid water mixing tanks is opened (in normal operation, No. 1 turbid water mixing tank 60 runs first, then No. 2 turbid water mixing tank 63 runs); when a low liquid level is detected in No. 2 water washing circulating mixing tank 36 (a delay running time is set, the time value can be set), the No. 2 water washing circulating mixing tank outlet pump 37 is stopped; (at this time, all the liquid separated by No. 2 centrifuge 29 enters the turbid water mixing tank). ⑤ Drying and material conveying control of centrifuge No. 29: After the water pump 37 of the No. 2 water washing circulating mixing tank stops, the signal is transmitted to centrifuge No. 29. Under the action of centrifugal force, the centrifuge separates the solid particles in the slurry from the liquid. During this process, heating and drying are carried out (the centrifugal drying time is adjustable). After drying, the material enters the No. 2 water washing mixing tank 38. ⑥ Liquid inlet control of No. 2 washing mixing tank 38: The pure water inlet of No. 2 washing mixing tank 38 is equipped with a pneumatic valve and an electromagnetic flow meter, and the tank body is equipped with a pressure level gauge (high, medium and low switch signals); during normal start-up, after the No. 2 centrifuge 29 stops working, the pure water inlet pneumatic valve is opened, and the inlet pneumatic valve is closed when the flow rate detected by the inlet electromagnetic flow meter reaches the set value (the flow rate value can be set) or reaches the high liquid level of No. 2 washing tank; ⑦ Interlocking control of mixer 38 in No. 2 water washing mixing tank: The mixer of No. 2 water washing mixing tank 38 is linked with the corresponding mixing tank pressure level gauge (open at mid-range, stop at low-range, pressure value can be set); ⑧ The No. 2 washing mixing tank 38 is operated in conjunction with the No. 3 centrifuge 30 after a delay: each time the No. 2 centrifuge 29 stops, the No. 2 washing mixing tank 38 runs for a set time (the delay time is set, and the time value can be set. This time is the running time of the No. 2 washing mixing tank) and then the signal is transmitted to the No. 3 centrifuge 30, and the centrifuge starts. Three-stage water washing circulation and water washing unit: ① Centrifuge No. 30 liquid diversion control: The outlet of centrifuge No. 30 is divided into two pipelines, one to two turbid water mixing tanks and the other to the No. 3 water washing circulation mixing tank 40. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 2 water washing circulation mixing tank 36 is started, the inlet pneumatic valve of the No. 3 water washing circulation mixing tank 40 is opened first, and the liquid separated by centrifuge No. 30 enters the No. 3 water washing circulation mixing tank 40. ② Circulation control of No. 3 water washing circulating mixing tank 40: A No. 3 water washing circulating mixing tank 40 is installed, with a pressure level gauge (high, medium, and low switching signals) on the tank body; a No. 3 water washing circulating mixing tank outlet pump 41 is installed at the tank outlet, pumping the liquid to the No. 3 centrifuge 30; in automatic operation, when the outlet pump of the No. 2 water washing mixing tank 38 is turned off (at this time, all the liquid separated by the No. 3 centrifuge 30 enters the No. 3 water washing circulating mixing tank 40), the No. 3 water washing circulating mixing tank outlet pump 41 is started, and the liquid in the tank enters the No. 3 water washing circulating mixing tank 40 again after passing through the No. 3 centrifuge 30; the circulation runs for a period of time, which is controlled by time (the time value can be set). ③ Control of the agitator in the No. 3 water washing circulating mixing tank 40: The No. 3 water washing circulating mixing tank 40 is equipped with one agitator, which starts when the liquid level in the tank is detected; when the No. 3 water washing circulating mixing tank outlet pump 41 stops, the agitator also stops running. ④ Liquid outlet switching control of No. 3 water washing circulating mixing tank 40: After the water pump 41 of No. 3 water washing circulating mixing tank runs for a set time, the inlet pneumatic valve on the tank body is closed; the pneumatic valve on the pipeline from the outlet of No. 3 centrifuge 30 to the two turbid water mixing tanks is opened (in normal operation, No. 1 turbid water mixing tank 60 runs first, and then No. 2 turbid water mixing tank 63 runs); when a low liquid level is detected in No. 3 water washing circulating mixing tank 40 (a delay running time is set, and the time value can be set), the water pump 41 of No. 3 water washing circulating mixing tank is stopped; (at this time, all the liquid separated by No. 3 centrifuge 30 enters the turbid water mixing tank). ⑤ Drying and material conveying control of centrifuge No. 30: After the water pump 41 of the No. 3 water washing circulating mixing tank stops, the signal is transmitted to centrifuge No. 30. Under the action of centrifugal force, the centrifuge separates the solid particles in the slurry from the liquid. During this process, heating and drying are carried out (the centrifugal drying time is adjustable). After drying, the material enters the No. 3 water washing mixing tank 42. ⑥ Liquid inlet control of No. 3 washing mixing tank 42: The pure water inlet of No. 3 washing mixing tank 42 is equipped with a pneumatic valve and an electromagnetic flow meter, and a pressure level gauge (high, medium and low switch signals) is installed on the tank body; during normal start-up, after the No. 3 centrifuge 30 stops working, the pure water inlet pneumatic valve is opened, and the inlet pneumatic valve is closed when the flow rate detected by the inlet electromagnetic flow meter reaches the set value (the flow rate value can be set) or reaches the high liquid level of No. 3 washing tank; ⑦ Interlocking control of mixer in No. 3 washing mixing tank 42: The mixer in No. 3 washing mixing tank 42 is linked with the corresponding mixing tank pressure level gauge (open at mid-range, stop at low-range, pressure value can be set). ⑧ The No. 3 washing mixing tank 42 is linked with the No. 4 centrifuge 31 after the No. 3 centrifuge 30 stops. After the No. 3 washing mixing tank 42 runs for a set time (the set delay time can be set, and this time is the running time of the No. 3 washing mixing tank), the signal is transmitted to the No. 4 centrifuge 31, and the centrifuge starts. S6 Four-Stage Water Washing Circulation and Discharge Unit: ① Liquid diversion control of centrifuge No. 4 31: The outlet of centrifuge No. 4 31 is divided into two pipelines, one to two turbid water mixing tanks and the other to the No. 4 water washing circulation mixing tank 44. Pneumatic valves are installed on the two pipelines respectively. In automatic operation, before the water pump of the No. 3 water washing circulation mixing tank 40 is started, the inlet pneumatic valve of the No. 4 water washing circulation mixing tank 44 is opened first, and the liquid separated by centrifuge No. 4 31 enters the No. 4 water washing circulation mixing tank 44. ② Circulation control of No. 4 water washing circulating mixing tank 44: One No. 4 water washing circulating mixing tank 44 is installed, with a pressure level gauge (high, medium, and low switching signals) on the tank body; a No. 4 water washing circulating mixing tank outlet pump 45 is installed at the tank outlet, pumping the liquid to the No. 4 centrifuge 31; in automatic operation, when the outlet pump of No. 3 water washing mixing tank 42 is turned off (at this time, all the liquid separated by the No. 4 centrifuge 31 enters the No. 4 water washing circulating mixing tank 44), the No. 4 water washing circulating mixing tank outlet pump 45 is started, and the liquid in the tank enters the No. 4 water washing circulating mixing tank 44 again after passing through the No. 4 centrifuge 31; the circulation runs for a period of time, which is controlled by time (the time value can be set). ③ Control of the mixer in the No. 4 water washing circulating mixing tank 44: The No. 4 water washing circulating mixing tank 44 is equipped with one mixer, which starts when the liquid level in the tank is detected; when the No. 4 water washing circulating mixing tank outlet pump 45 stops, the mixer also stops running. ④ Liquid discharge switching control of No. 4 water washing circulating mixing tank 44: After the No. 4 water washing circulating mixing tank outlet pump 45 runs for the set time, close the inlet pneumatic valve on the tank body; open the pneumatic valve on the pipeline from the outlet of No. 4 centrifuge 31 to the two turbid water mixing tanks (in normal operation, No. 1 turbid water mixing tank 60 runs first, then No. 2 turbid water mixing tank 63 runs); when a low liquid level is detected in the No. 4 water washing circulating mixing tank 44 (a delay running time is set, the time value can be set), stop the No. 4 water washing circulating mixing tank outlet pump 45; (at this time, all the liquid separated by No. 4 centrifuge 31 enters the turbid water mixing tank). ⑤ Drying and discharge control of centrifuge No. 4 31: After the water pump 45 of the No. 4 water washing circulating mixing tank stops, the signal is transmitted to centrifuge No. 4 31. Under the action of centrifugal force, the centrifuge separates the solid particles in the slurry from the liquid. During this process, heating and drying are carried out (the centrifugal drying time is adjustable). After drying, the material enters the equipment of the next process. ⑥ Process linkage control of centrifuge No. 4 31: The operation signal of centrifuge No. 4 31 is fed back to the equipment of the next process to ensure the continuity of the process line; S4 acid recovery treatment: ① Waste acid mixing tank inlet control: The outlet of centrifuge 28 is connected to two waste acid mixing tanks. Pneumatic valves are installed at the inlet of each tank. Magnetic level gauges (high and low switch signals) are installed on each waste acid mixing tank. During normal operation, waste acid mixing tank 50 is started first, followed by waste acid mixing tank 53. When the liquid level in waste acid mixing tank 50 reaches the high level, the pneumatic valve for the inlet of waste acid mixing tank 50 is closed, while the pneumatic valve for the inlet of waste acid mixing tank 53 is opened. ② Ceramic membrane equipment 49 linkage control: The level signals of the magnetic flip plates on the two waste acid mixing tanks are transmitted to ceramic membrane equipment 49; the waste acid booster pump and the two concentrate booster pumps are controlled by ceramic membrane equipment 49; during normal operation, when any waste acid tank has a high level, the corresponding outlet pneumatic valve opens, and the operation signal is fed back to the ceramic membrane equipment; at this time, the ceramic membrane starts to work and controls the operation of the waste acid booster pump. When the ceramic membrane circulates until the concentrate reaches the required level, the waste acid booster pump is turned off, and the pneumatic valves before and after the concentrate booster pump and the water pump of the corresponding tank are opened; ③ Control of No. 1 50% concentrated acid solution mixing tank 26: The concentrated solution is pumped to No. 1 50% concentrated acid solution mixing tank 26. No. 1 50% concentrated acid solution mixing tank 26 is equipped with a magnetic level gauge (high, medium, and low switching signals). The signal is transmitted to No. 1 centrifuge 28 (medium-level start, low-level stop), and simultaneously to the two concentrated solution pumps (low-level start, high-level stop). The operation of the 50% concentrated acid solution pump is controlled by No. 1 centrifuge 28. During normal operation, when the liquid level in No. 1 50% concentrated acid solution mixing tank 26 reaches the specified level, the operation signal is transmitted to No. 1 centrifuge 28, and the centrifuge is running, the 50% concentrated acid solution pump can only be started. Under normal circumstances, the 50% concentrated acid solution pump cannot operate independently. First, the liquid level condition in No. 1 50% concentrated acid solution mixing tank 26 must be met. Second, the 50% concentrated acid solution pump can only be started when the water pump from No. 1 pickling mixing tank 5 or No. 2 pickling mixing tank 6 is working. ④ Control of acid recovery storage tank 25: The clear liquid outlet of the No. 1 ceramic membrane device 49 is connected to the acid recovery storage tank 25. The tank is equipped with a magnetic level gauge (high, medium and low switching signals). During normal operation, when the medium level condition is met, the signal is transmitted to the waste acid recovery device to start operation, and the acid regeneration booster pump 24 is started at the same time; when the acid recovery storage tank 25 is at a low level, the acid regeneration booster pump 24 stops. ⑤ Waste acid recovery device diversion control: The waste acid recovery device has two pipelines for water discharge. One pipeline separates the recyclable acid into the recovery acid tank 19, and the other pipeline separates the non-recyclable acid into the acid treatment raw water tank 22. The two tanks are equipped with magnetic float level gauges (high, medium and low switch signals). When either tank reaches the high level, the waste acid recovery device stops running, and the front-end acid regeneration booster pump 24 stops at the same time. ⑥ Recirculation control of acid recovery tank 19: A magnetic level gauge (high, medium and low switching signals) is installed on acid recovery tank 19, and an acid recovery booster pump 20 is installed, with the pump outlet pipeline connected to acid dilution and mixing tank 10; it is controlled by the liquid level of acid recovery tank 19 (medium opening, low stopping) and simultaneously controlled by the liquid level of acid dilution and mixing tank 10 (low opening, high stopping). ⑦ Linkage control of acid treatment raw water tank 22: The acid treatment raw water tank 22 is equipped with a magnetic float level gauge (high, medium and low switch signals). The signal is transmitted to the waste acid recovery device (low start, high stop) and simultaneously to the subsequent acid treatment equipment (medium start, low stop) to ensure the continuity of the process line. S5 washing and turbid water treatment: ① Turbid water tank inlet control: The centrifuge outlets of No. 1 washing mixing tank 34, No. 2 washing mixing tank 38, No. 3 washing mixing tank 42, and No. 4 washing mixing tank 44 are connected in parallel and then fed into two turbid water tanks respectively. Pneumatic valves are installed at the inlet of each tank, and magnetic float level gauges (high and low switch signals) are installed on each tank. During normal operation, No. 1 turbid water mixing tank 60 is started first, followed by No. 2 turbid water mixing tank 63. When the liquid level in No. 1 turbid water mixing tank 60 reaches the high level, the inlet pneumatic valve of No. 1 turbid water mixing tank 60 is closed, while the inlet pneumatic valve of No. 2 turbid water mixing tank 63 is opened. ② Ceramic membrane equipment 58 linkage control: The liquid level signals of the magnetic flip plates on the two turbid water tanks are respectively transmitted to the ceramic membrane equipment 58; the turbid water tank lift pump 59 and the concentrate outlet pumps of the two turbid water tanks are controlled by the ceramic membrane equipment 58; during normal operation, no matter which turbid water tank has a high liquid level, the corresponding outlet pneumatic valve opens, and the operation signal is fed back to the ceramic membrane equipment; at this time, the ceramic membrane starts to work and controls the operation of the turbid water tank lift pump 59. When the ceramic membrane circulates until the concentrate reaches the required level, the turbid water tank lift pump 59 closes, and the concentrate outlet pump of the corresponding tank and the pneumatic valves before and after the pump are opened; ③ Control of unqualified water return from the turbid water tank: The turbid water tank is equipped with an unqualified water lift pump 55. The pipeline outlet is split into two pipelines to two pickling mixing tanks respectively. Pneumatic valves are installed on each pipeline. When the sampling detects that the solution in the tank is not up to standard or the membrane treatment equipment is abnormal, the valves and water pumps are manually opened. S6 concentrate circulation: The concentrate from the turbid water tank is pumped to the No. 2 50% concentrated acid solution mixing tank 64. The No. 2 50% concentrated acid solution mixing tank 64 is equipped with a magnetic level gauge (high, medium, and low switching signals). The signal is transmitted to the No. 2 centrifuge 29 (medium-level start, low-level stop) and simultaneously to the two turbid water tank concentrate outlet pumps (low-level start, high-level stop). The No. 2 centrifuge 29 controls the operation of the No. 2 50% concentrated acid solution booster pump 65. During normal operation, when the liquid level in the No. 2 50% concentrated acid solution mixing tank 64 is reached, the operation signal is transmitted to the No. 2 centrifuge. 29. The No. 2 50% concentrated acid solution booster pump 65 can only be started when the centrifuge is running. Under normal circumstances, the No. 2 50% concentrated acid solution booster pump 65 cannot be operated alone. First, the liquid level in the No. 2 50% concentrated acid solution mixing tank 64 must be met. Second, the No. 2 50% concentrated acid solution booster pump 65 can only be started when the water pump of the No. 1 water washing mixing tank 34 is working, so that the 50% concentrated acid solution can be pumped to the centrifuge for separation. The separated acid solution is then transported back to the acid washing unit for reuse through pipelines. Example

[0040] Low-concentration inorganic acid + metal chelating agent composite pickling solution (replacement for traditional concentrated acid pickling): The core of this solution is to use a low-concentration inorganic acid and metal chelating agent compound system to replace the traditional high-concentration single acid solution. Impurities are removed through the dual action of "acid washing and dissolution + chelation and capture", which solves the problem of low removal rate caused by the corrosion of equipment by traditional concentrated acid and the adsorption of iron ions, while achieving the same or even better purification effect.

[0041] Specific process details: 1. Pickling medium: Composed of an aqueous solution of inorganic acid and metal chelating agent, wherein the mass percentage of inorganic acid is 0.05% to 0.5% and the mass percentage of metal chelating agent is 0.01% to 0.1%; the inorganic acid is mainly sulfuric acid (60% to 90% molar percentage), and one or more of hydrochloric acid and nitric acid can be used as minor components; the metal chelating agent is selected from one or more of disodium ethylenediaminetetraacetate, sodium gluconate, sodium tartrate, and sodium citrate.

[0042] 2. Process Flow: Silicon nitride powder (median particle size 0.3~20μm, iron impurity content 0.01~0.1%) is added to a compound pickling medium to prepare a slurry with a powder mass ratio of 1~10%. The slurry is placed in a reactor and stirred, with the temperature controlled at 20~120℃ and the stirring time at 0.5~5h. Iron impurities are dissolved by acid washing, and iron ions are captured by a chelating agent (to avoid adsorption on the powder surface). The slurry is then pumped into a filter for filtration, washed with deionized water until the pH of the filtrate is 6~7, and finally vacuum dried (vacuum degree 0.1~1Pa, two-stage drying: drying at 40~60℃ for 6~12h, and then heating to 100~120℃ for 2~4h) to obtain purified silicon nitride powder.

[0043] 3. Equipment replacement: There is no need to replace the original pickling line's reaction vessel, filter, and drying equipment. Only a new chelating agent metering and adding device needs to be added to adapt to the original production line's continuous feeding and discharging rhythm. It can directly replace the traditional concentrated acid storage tank and metering device, reducing the risk of equipment corrosion.

[0044] 4. Technical Evidence: The iron impurity removal rate can reach over 99%, reducing the iron impurity content to below 0.01%. The acid consumption is reduced by over 80% compared to the traditional concentrated acid solution, the equipment corrosion rate is reduced by 70%, and the powder dispersibility is not affected. It fully matches the core technical effect of the original pickling line.

[0045] Example 3 High-energy ultrasonic-assisted acid washing solution (an alternative to conventional agitation acid washing): The core of this solution is to retain the original pickling medium (single acid or mixed acid) and replace conventional mechanical stirring with "high-energy ultrasound". Ultrasonic vibration strengthens the contact between the acid and the powder surface, destroys the binding force between impurities and powder, improves the microstructure of powder, and enhances the impurity removal efficiency. It is especially suitable for the purification of silicon nitride powder with fine particle size and high impurity content.

[0046] Specific process details: 1. Pickling medium: Two or three mixed acids from HF, HCl and HNO3 can be selected. With HF as the reference, the mass ratio of each acid is HF:HCl:HNO3=1:0.75~20:0~25, and the mass ratio of acid to silicon nitride powder is 1~10:1. It can also be adapted to the low concentration compound acid system of Scheme 1, with strong compatibility.

[0047] 2. Process Flow: After mixing silicon nitride powder with pickling medium, it is fed into an ultrasonic pickling tank. The ultrasonic temperature is controlled at 40~60℃ and the ultrasonic time is 1~10h (preferably 1~3h). The cavitation effect of ultrasound is used to peel off the oxide layer and adsorbed impurity particles on the powder surface. After pickling, it is diluted with distilled water 1~5 times, then neutralized with ammonia water 1~3 times, and finally washed until pH=7. After drying and grinding, high-purity powder is obtained. It can be combined with a two-stage nitriding process to further reduce the free silicon content and increase the α phase ratio of the powder (≥93%).

[0048] 3. Equipment replacement: Replace the mechanical stirring device of the original pickling line and add a high-energy ultrasonic generator (power adjustable to match the production line capacity). The pickling tank can use the original equipment, only the ultrasonic transducer installation interface needs to be added; there is no need to modify the subsequent equipment such as filtration and drying, and it can be directly connected to the original continuous production line.

[0049] 4. Technical Evidence: The impurity removal efficiency is 30% to 50% higher than that of conventional stirring pickling, the pickling time is shortened by more than 40%, the powder surface is smoother, the free silicon content can be reduced to below 0.5%, and the α phase ratio is stabilized at more than 93%, meeting the purity requirements of high-end silicon nitride powder. The technical effect is consistent with and better than that of the original pickling line.

[0050] Example 4 Microgravity filtration equipment as an alternative to dynamic cross-flow ceramic membranes (replacing powder interception equipment): The core of this solution is to completely replace the dynamic cross-flow membrane filtration unit in the original pickling line with a microgravity filtration device. By leveraging the microgravity field, the solid-liquid separation effect is enhanced, resolving the corrosion of the ceramic membrane of the dynamic cross-flow membrane caused by excessively high fluoride ion concentrations in the pickling solution, and simultaneously eliminating the need for frequent cleaning. The original pickling medium and core process flow are retained, achieving equal or even better solid-liquid separation and impurity retention effects, making it suitable for continuous industrial production.

[0051] Specific process details: 1. Pickling medium: It can be fully adapted to two or three mixed acids in HF, HCl and HNO3 without adjusting the medium formula and concentration. It has extremely strong compatibility and does not change the original chemical / physical mechanism of impurity removal.

[0052] 2. Process Flow: Following the original scheme's pre-process steps of pickling / stirring / ultrasonication / ball milling, after the powder and medium have fully reacted and impurities have been fully dissolved / removed, the clear liquid is pumped into a microgravity filtration device. The microgravity field strength is controlled at 10–50 g (adjustable according to slurry concentration and powder particle size), the filtration temperature is the same as the pre-reaction temperature (20–120℃), and the filtration pressure is 0.1–0.3 MPa. Utilizing the mechanical interception effect of the microgravity device, solid-liquid separation is accelerated, retaining powder particles while allowing the acidic liquid containing impurities to pass smoothly through the filter medium, achieving efficient separation of powder and impurity liquid. After filtration, deionized water is directly used for online backwashing within the device (backwashing pressure 0.2–0.4 MPa, backwashing time 5–10 min), without disassembling the device. Subsequently, the retained powder is sent to the subsequent drying unit to complete the purification process.

[0053] 3. Equipment Replacement: Completely replace the dynamic cross-flow membrane modules, membrane filter supports, and membrane cleaning devices in the original pickling line, and add microgravity filtration equipment (including microgravity generating unit, filter chamber, online backwashing system, and slurry inlet and outlet pipelines); no modification is required to the pre-reaction equipment (stirring tank, ultrasonic tank, centrifuge equipment, etc.) and subsequent drying and grinding equipment, only the interface of the slurry conveying pipeline needs to be adjusted to adapt to the continuous feeding and discharging rhythm of the original production line; the microgravity filtration equipment can be selected with a single-chamber or multi-chamber parallel structure according to the production line capacity to adapt to different processing capacity requirements.

[0054] 4. Technical Evidence: It can be used stably and continuously in 2% hydrofluoric acid pickling solution, completely solving the membrane corrosion problem. The equipment cleaning frequency is reduced from once every 8 hours to once every 48 hours, significantly reducing operation and maintenance costs. The powder retention rate is ≥99.5%, and the impurity removal effect is consistent with the original dynamic cross-flow membrane filtration, fully matching the core technical effect of the original pickling line. Moreover, the equipment has a longer service life and is more convenient to operate and maintain.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A closed multi-stage washing silicon nitride powder pickling production line, characterized in that: The production line includes an acid pickling unit, an acid recovery unit, a turbid water treatment unit, a multi-stage water washing unit, and a concentrated liquid treatment unit. The pickling unit includes a hydrofluoric acid storage tank (12), a hydrochloric acid storage tank (16), a hydrofluoric acid metering tank (14), a hydrochloric acid metering tank (18), an acid dilution mixing tank (10), a first pickling stirring tank (5), a second pickling stirring tank (6), a first centrifuge (28), and a second centrifuge (29). The hydrofluoric acid storage tank (12) is connected to the hydrofluoric acid metering tank (14) via a hydrofluoric acid booster pump (11), and the hydrochloric acid storage tank (16) is connected to the hydrochloric acid metering tank (18) via a hydrochloric acid booster pump (15). 4) The first hydrofluoric acid metering pump (13) and the hydrochloric acid metering tank (18) are connected to the acid dilution mixing tank (10) via the first hydrochloric acid metering pump (17). The acid dilution mixing tank (10) is connected to the first pickling stirring tank (5) and the second pickling stirring tank (6) in sequence via the acid dilution tank outlet pump (9). The outlet of the first pickling stirring tank (5) is connected to the first centrifuge (28) via the first pickling stirring tank outlet pump (4). The outlet of the second pickling stirring tank (6) is connected to the second centrifuge (29) via the second pickling stirring tank outlet pump (7). The acid recovery unit includes an acid recovery tank (19), an acid treatment raw water tank (22), an acid recovery device (23), and an acid recovery storage tank (25). The acid recovery tank (19) is connected to the acid treatment raw water tank (22) via an acid recovery booster pump (20). The acid treatment raw water tank (22) is connected to the acid recovery device (23) via an acid treatment booster pump (21). The outlet of the acid recovery device (23) is connected to the acid recovery storage tank (25) via an acid regeneration booster pump (24). The acid recovery storage tank (25) is connected to the No. 1 50% concentrated acid mixing tank (26) and the No. 2 50% concentrated acid mixing tank (64) respectively. The turbid water treatment unit includes a first turbid water mixing tank (60), a second turbid water mixing tank (63), a first ceramic membrane device (49), a second ceramic membrane device (58), and a clean water tank (56). The first turbid water mixing tank (60) and the second turbid water mixing tank (63) are respectively connected to the first ceramic membrane device (49) and the second ceramic membrane device (58) via a turbid water lift pump (59). The clean water outlets of the first ceramic membrane device (49) and the second ceramic membrane device (58) are both connected to the clean water tank (56) via a clean water lift pump (54). The first ceramic membrane forward wash water tank (47) and the second ceramic membrane forward wash water tank (57) are respectively connected to the first ceramic membrane device (49) and the second ceramic membrane device (58). The multi-stage washing unit includes a No. 1 washing mixing tank (34), a No. 2 washing mixing tank (38), a No. 3 washing mixing tank (42), a No. 4 washing mixing tank (44), a No. 3 centrifuge (30), and a No. 4 centrifuge (31). The pure water storage tank (1) is connected to the No. 1 washing circulating mixing tank (32), the No. 2 washing circulating mixing tank (36), the No. 3 washing circulating mixing tank (40), and the No. 4 washing circulating mixing tank (44) via the pure water storage tank outlet pump (8). The No. 1 washing circulating mixing tank (32) is connected to the No. 1 washing mixing tank (34) via the No. 1 washing circulating mixing tank outlet pump (33). The No. 2 washing tank (38) is connected to the No. 4 washing mixing tank (34). The washing circulation mixing tank (36) is connected to the No. 2 washing circulation mixing tank (38) via the No. 2 washing circulation mixing tank outlet pump (37). The No. 3 washing circulation mixing tank (40) is connected to the No. 3 washing circulation mixing tank (42) via the No. 3 washing circulation mixing tank outlet pump (41). The No. 4 washing circulation mixing tank (44) is connected to the No. 4 washing mixing tank (44) via the No. 4 washing circulation mixing tank outlet pump (45). The outlets of the No. 1 washing mixing tank (34) and the No. 2 washing mixing tank (38) are connected to the No. 3 centrifuge (30). The outlets of the No. 3 washing mixing tank (42) and the No. 4 washing mixing tank (44) are connected to the No. 4 centrifuge (31). The concentrated liquid treatment unit includes a No. 1 waste acid mixing tank (50), a No. 2 waste acid mixing tank (53), a No. 1 50% concentrated acid mixing tank (26), and a No. 2 50% concentrated acid mixing tank (64). The concentrated liquid outlets of the No. 1 ceramic membrane device (49) and the No. 2 ceramic membrane device (58) are respectively connected to the No. 1 waste acid mixing tank (50) and the No. 2 waste acid mixing tank (53). The No. 1 waste acid mixing tank (50) is connected to the No. 1 concentrated liquid booster pump (51) and the No. 2 waste acid mixing tank (64). (53) The No. 1 50% concentrated acid solution stirring tank (26) and the No. 2 50% concentrated acid solution stirring tank (64) are connected by the No. 2 concentrated solution booster pump (52). The No. 1 50% concentrated acid solution stirring tank (26) is returned to the pickling unit by the No. 1 50% concentrated acid booster pump (27) and the No. 2 50% concentrated acid solution stirring tank (64) by the No. 2 50% concentrated acid booster pump (65). The outlet end of the No. 2 50% concentrated acid booster pump (65) is connected to an external centrifuge. The pure water storage tank (1) is connected to the cleaning interfaces of each mixing tank and the pipeline through the tank cleaning pump (2), the pipeline cleaning water pump (3), and the mixing tank flushing water outlet pump (46). The clean water tank (56) is returned to the turbid water treatment unit through the turbid water tank unqualified lift pump (55). The outlet ends of the entire line of lift pump, circulation pump, outlet pump, water tank, mixing tank and storage tank are all equipped with control valves.

2. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: The outlet of the acid treatment booster pump (21) is connected to an external non-recoverable acid treatment device.

3. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: The pure water storage tank (1) is connected to the external reverse osmosis water outlet pipe.

4. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: The inlet of the water purification pump (54) is connected to the water supply pipeline of the radiator in the plant area, and the unqualified turbid water tank booster pump (55) is connected to the acid treatment raw water tank.

5. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: The discharge end of the fourth centrifuge (31) is connected to an external drying device.

6. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: The first pickling mixing tank (5) and the second pickling mixing tank (6) of the pickling unit are connected in series and are closed structures. The inner walls of the mixing tanks are made of corrosion-resistant materials.

7. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: The No. 1 ceramic membrane device (49) and the No. 2 ceramic membrane device (58) of the turbid water treatment unit are connected in parallel and have online backwashing function.

8. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: The multi-stage washing unit is a four-stage continuous countercurrent washing structure, and each stage of the washing mixing tank is equipped with an online conductivity and pH detection probe.

9. The closed-loop multi-stage washing production line for silicon nitride powder pickling according to claim 1, characterized in that: Centrifuge No. 1 (28), centrifuge No. 2 (29), centrifuge No. 3 (30), and centrifuge No. 4 (31) are all corrosion-resistant, sealed centrifuges.

10. A production process for a closed-loop multi-stage washing silicon nitride powder pickling production line according to any one of claims 1-9, characterized in that: The production process includes the following steps: S1 Acid preparation: After metering, the acid solution is sent to a dilution mixing tank and mixed with pure water to form a mixed acid solution, which is then transported to a closed acid washing stirring assembly; S2 Multi-stage closed acid washing: Silicon nitride powder is added to the closed acid washing stirring assembly and stirred thoroughly with the mixed acid solution. After the reaction, the powder and waste acid solution are separated by centrifugation; S3 Multi-stage continuous countercurrent water washing: The powder after acid washing is sequentially sent to a multi-stage water washing stirring assembly and washed with pure water in a countercurrent manner. The conductivity and pH are monitored in real time during the washing process. After washing, the powder and turbid water are separated by centrifugation. S4 acid recovery and treatment: Waste acid is collected and concentrated by membrane separation. The concentrated acid is returned to the pickling unit for reuse. The clear liquid is recycled after acid regeneration. Non-recoverable acid is sent to external treatment. S5 Washing Turbid Water Treatment: The washing turbid water is collected and separated by membrane separation to obtain purified water and concentrated liquid. The purified water is reused in the production line, and the concentrated liquid is sent to the concentrated liquid treatment unit. S6 Concentrated Liquid Circulation: The membrane separation concentrated liquid is collected, concentrated, and returned to the pickling unit for reuse.

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