A method for treating iron-containing waste hydrochloric acid

Abstract

The present invention relates to the technical field of waste hydrochloric acid resource utilization, and discloses a method for treating waste hydrochloric acid containing iron, (i) in the tempering stage, waste hydrochloric acid containing iron from different sources is mixed, and the iron content is adjusted according to production requirements; (ii) in the catalytic oxidation stage, a catalyst is added to the waste hydrochloric acid containing iron, the temperature is controlled within 75°C, and the pressure is controlled to be 0.02-0.03Mpa by introducing oxygen, and the divalent iron ions in the waste hydrochloric acid are oxidized to trivalent iron ions for 3-4 hours to obtain a reaction solution; (iii) in the post-processing stage: the reaction solution is adjusted by adding liquid alkali to obtain ferric chloride or polyferric chloride liquid. This scheme optimizes catalytic oxidation, while ensuring the oxidation effect, effectively shortening the batch processing time and improving production efficiency. Specifically, when this scheme actually adopts catalytic oxidation to treat waste hydrochloric acid containing iron to produce ferric chloride water treatment agent, the product yield can reach 11-12t / 8h, and three batches can be produced every day, so that the product yield of ferric chloride water treatment agent is as high as 35-36t / d, which significantly improves production efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of resource utilization of waste hydrochloric acid, and in particular to a method for treating iron-containing waste hydrochloric acid. Background Art

[0002] As a commonly used chemical product, hydrochloric acid is widely used in pickling processes such as cold rolling and galvanizing of carbon steel. During the pickling process, hydrochloric acid and the surface of steel undergo multiple reactions to generate ferrous chloride and ferric chloride and dissolve in the acid solution. The hydrochloric acid waste liquid produced by this reaction has a low zinc content and contains 5-16% ferrous chloride and ferric chloride. However, these waste hydrochloric acids have high iron content and low hydrochloric acid concentration, and lack direct industrial application value; if this part of the iron-containing hydrochloric acid waste liquid is directly discharged, it will cause serious environmental pollution to the discharge area. In addition, the ferrous chloride and hydrogen chloride contained in the waste acid are very good chemical raw materials. Therefore, the resource treatment and utilization of iron-containing waste hydrochloric acid is particularly important in protecting the environment and achieving green development.

[0003] Prior art CN110316766A discloses a method for preparing ferric chloride products by two-stage oxidation of iron-containing waste hydrochloric acid, comprising the following steps: step 1, the iron-containing waste hydrochloric acid is pretreated through a filtering device; step 2, the pretreated iron-containing waste hydrochloric acid enters a catalytic oxidation tank and is heated to make the temperature of the iron-containing waste hydrochloric acid reach 60-95°C, and compressed air or oxygen is introduced for catalytic oxidation, the pressure in the catalytic oxidation tank is 0.15-0.25MPa, and the catalytic oxidation time is 3-7h; step 3, the ferrous ion content is tested, and an oxidant is added according to the test result for chemical oxidation, the oxidation time is 1-2h, and the obtained ferric chloride liquid product meets the product requirements of GB4482-2006. In step 2, the iron-containing waste hydrochloric acid after catalytic oxidation is partially transported to the chemical oxidation tank for chemical oxidation in step 3, and at the same time, the pretreated iron-containing waste hydrochloric acid in step 1 is partially transported to the catalytic oxidation tank for catalytic oxidation.

[0004] However, the above scheme still has the following problems: the prior art requires two-stage oxidation to obtain a ferric chloride solution that meets the requirements. On the one hand, it not only has many types of oxidants, but also has a large amount of each oxidant and high cost; on the other hand, its process is complicated and the oxidation time is long, the energy consumption is high, and the efficiency is low. The applicant has also made improvements (CN114804426A a kind of iron-containing waste hydrochloric acid treatment process), and used sodium chlorate oxidation method to treat iron-containing waste hydrochloric acid to produce iron chloride related water treatment agent products. However, the sodium chlorate oxidation method not only has a high reagent cost, but also in the case of graphite heat exchanger heat exchange, it still takes 24h to process each batch of 10-12t iron-containing waste hydrochloric acid. If the graphite heat exchanger is not used, it takes 48h to cool naturally, and its overall efficiency is still low.

[0005] In view of this, therefore, developing a method for treating iron-containing waste hydrochloric acid with a simple process flow and high efficiency not only effectively makes up for the shortcomings of the existing technology, but also has important significance for fully tapping the resource utilization potential of iron-containing waste hydrochloric acid. Summary of the invention

[0006] The present invention aims to provide a method for treating iron-containing waste hydrochloric acid to solve the technical problem of low efficiency in treating iron-containing waste hydrochloric acid to produce ferric chloride water treatment agent in the prior art.

[0007] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a method for treating iron-containing waste hydrochloric acid, comprising the following steps: (i) a tempering stage, mixing iron-containing waste hydrochloric acid from different sources, adjusting the iron content according to production requirements and filtering the iron-containing waste hydrochloric acid by plate and frame; (ii) a catalytic oxidation stage, adding a catalyst to the iron-containing waste hydrochloric acid, controlling the temperature within 75°C, introducing oxygen to control the pressure at 0.02-0.03Mpa, reacting for 3-4 hours to oxidize the divalent iron ions in the waste hydrochloric acid into trivalent iron ions, and obtaining a reaction solution; (iii) a post-treatment stage: the reaction solution is subjected to the salt base adjustment by adding liquid alkali to obtain ferric chloride or polyferric chloride liquid.

[0008] The principles and advantages of this solution are:

[0009] 1. Compared with the low efficiency of the prior art sodium chlorate oxidation method for treating iron-containing waste hydrochloric acid to produce iron chloride water treatment agent, this scheme optimizes catalytic oxidation, effectively shortens the batch processing time while ensuring the oxidation effect, and improves production efficiency. Specifically, when this scheme actually uses catalytic oxidation to treat iron-containing waste hydrochloric acid to produce iron chloride water treatment agent, the product yield can reach 11-12t / 8h, and three batches can be produced every day, making the product yield of iron chloride water treatment agent as high as 35-36t / d, significantly improving production efficiency.

[0010] 2. Compared with the prior art that uses composite oxidants or high-cost oxidants such as sodium chlorate to increase costs, the catalytic oxidation of this scheme only requires low-cost oxygen as an oxidant throughout the process, and controls the oxygen pressure to 0.02-0.03Mpa (specifically controlled to 0.02MPa during production). By selecting low-cost oxidants and reducing the amount of oxygen used, the overall cost of the oxidant is effectively reduced, thereby effectively improving production efficiency. The applicant has found through long-term experiments that the catalytic oxidation equipment used in the scheme mainly depends on the air intake of the ejector. If the set catalytic oxidation pressure is too low, the oxygen consumption will be too large due to the excessive reaction speed in the middle stage of the reaction, and the pressure may drop too fast or even negative pressure or vacuum may occur. In this case, the risk of tank rupture will increase, increasing safety hazards; taking a step back, even if the one-way air intake valve set in the equipment can avoid equipment damage, the one-way air intake valve inhales air, and air entering the equipment will also reduce the reaction efficiency and affect the reaction effect. If the set catalytic oxidation pressure is too high, excess oxygen needs to be discharged after the reaction is completed, resulting in oxygen waste and increased costs.

[0011] Preferably, as an improvement, in the (i) conditioning stage, waste hydrochloric acid containing iron from different sources is conditioned into three types of solutions, wherein the total iron content in the first type of solution is ≥15.6%, which is used to produce ferric chloride; the total iron content in the second type of solution is 12% to 15.6%, which is used to produce polyferric chloride water treatment agent; the total iron content in the third type of solution is 8% to 12%, which is used to produce polyferric chloride water treatment agent with a polyferric chloride content higher than 8%, or is mixed with the second type of solution to prepare a raw material with a total iron content greater than 12%, which is used to produce polyferric chloride water treatment agent.

[0012] Beneficial effect: This scheme adopts the above-mentioned setting, which is convenient for rationally planning waste hydrochloric acid containing 5-16% total iron from different sources, helps to directly produce different products that meet the needs of different customer orders, realizes personalized resource utilization of iron-containing waste hydrochloric acid, effectively reduces the production process and improves production efficiency.

[0013] Preferably, as an improvement, in the (ii) catalytic oxidation stage, the catalyst is sodium nitrite, and the amount of catalyst added is 2 to 3‰ of the total weight of the iron-containing waste hydrochloric acid.

[0014] Technical effect: Nitrite ion (NO2 - ) has strong oxidizing properties and can convert ferrous ions (Fe 2+ ) is oxidized to iron ions (Fe 3+ ), and at the same time it is reduced to nitrogen (N2) or nitric oxide (NO). This scheme adopts the above settings, and uses sodium nitrite to convert ferrous ions (Fe 2+ ) is rapidly oxidized to iron ions (Fe 3+), speed up the reaction process and improve production efficiency. The applicant has found through long-term experiments that if the amount of sodium nitrite is too low, the oxidation will be incomplete and slow due to insufficient catalyst, while if the amount of sodium nitrite is too high, excessive nitrogen dioxide gas will be generated, resulting in yellow smoke and a pungent odor in the product.

[0015] Preferably, as an improvement, in the (ii) catalytic oxidation stage, the endpoint of the catalytic oxidation is that the pressure rises and stabilizes for 5 to 10 minutes, and the reaction is stopped when the ferrous ion content in the waste hydrochloric acid meets the requirements of sampling and testing: when producing polyferric chloride, the ferrous ion content is controlled to be ≤0.2%; when producing ferric chloride, the ferrous ion content is controlled to be ≤0.1%.

[0016] Beneficial effect: This scheme adopts the above setting to facilitate full oxidation to the ferrous content to meet the requirements of "HG / T 4672-2022 Water Treatment Agent Polyferric Chloride" or "GB / T 4482-2018 Water Treatment Agent Ferric Chloride", ensuring product quality.

[0017] Preferably, as an improvement, in the (ii) catalytic oxidation stage, the catalytic oxidation is completed in a catalytic oxidation tank, which includes a tank body, a circulation unit connected to the tank body, an ejector connected between the tank body and the circulation unit, and an acceleration reactor connected to the lower part of the ejector, wherein the acceleration reactor is located in the tank body; an intake pipe connected to the tank body is provided on the side of the ejector, and a one-way valve is provided on the intake pipe.

[0018] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for circulating the waste hydrochloric acid in the tank to the ejector and mixing it with the oxygen sucked from the tank to complete the oxidation reaction. Specifically, the circulation unit realizes the circulation of waste hydrochloric acid in the tank and the ejector. The ejector is used to eject the circulated waste hydrochloric acid into the tank, and forms a negative pressure in the process, so that the oxygen in the tank is sucked into the ejector from the air intake pipe to mix with the waste hydrochloric acid. And this scheme uses the negative pressure to suck oxygen reaction, which is convenient for fully oxidizing the ferrous ions that are not fully oxidized in the tank into ferric ions, thereby ensuring that the single-stage oxidation can achieve the full oxidation of the divalent iron ions in the waste hydrochloric acid into ferric ions, without the need to set up multi-stage oxidation, effectively simplifying the process flow, reducing equipment requirements and time costs, and improving production efficiency.

[0019] Preferably, as an improvement, the acceleration reactor includes an integrally formed straight tube and a curved tube, the straight tube portion is fixed with an inverted cone tube, the mouth of the inverted cone tube is in the shape of an inverted cone; a plurality of curved tubes are provided, which are evenly distributed around the straight tube in a circular direction with the straight tube as a circle, and the mouth of the curved tube is upwardly tilted.

[0020] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for pressurizing the waste hydrochloric acid injected into the tank by the ejector, thereby forming suction and sucking the oxygen in the tank to react in the ejector. Specifically, the waste hydrochloric acid ejected from the ejector is sprayed onto the inner wall of the inverted cone tube, and the shape of the inverted cone tube can once again play a role in collecting and pressurizing the waste hydrochloric acid, so that the waste hydrochloric acid is accelerated to flow out of the ejector, so that the gas inside the ejector is quickly flushed out and becomes a negative pressure state, so that the oxygen in the tank can quickly enter the ejector along the suction pipe to react with the waste hydrochloric acid, effectively increasing the speed of oxygen entering the ejector, thereby improving the reaction efficiency. A bent pipe is arranged under the straight pipe, so that after the waste hydrochloric acid flows into the straight pipe, it can flow to the pipe mouth along the arc inner wall of the bent pipe. On the one hand, the smoothness of the waste hydrochloric acid flowing out of the bent pipe can be improved, the flow rate of the waste hydrochloric acid can be accelerated, and the circulation efficiency can be improved; on the other hand, the pipe mouth of the bent pipe is tilted upward, so that the waste hydrochloric acid tends to spray upward after being sprayed out, so that it can have a positive contact with the oxygen introduced from the top of the tank body, thereby increasing the contact area between the waste hydrochloric acid and oxygen, and further improving the reaction rate.

[0021] Preferably, as an improvement, the circulation unit includes a discharge pipe connected to the bottom of the tank body, a circulation pump connected to the discharge pipe, a feed pipe connected between the circulation pump and the ejector, and an output pipe connected to the feed pipe. Multiple circulation pumps can be provided, and valves are provided on the feed pipe and the output pipe.

[0022] Technical effect: This scheme adopts the above-mentioned setting, which makes it easy to extract the waste hydrochloric acid in the tank body and send it into the ejector from the top of the tank body. After being injected into the tank body through the ejector, it reacts with oxygen to accelerate the reaction, and then returns to the tank body to replenish and accelerate the circulation of the waste hydrochloric acid, thereby accelerating the reaction rate.

[0023] Preferably, as an improvement, a liquid inlet and an air inlet are provided on the top of the tank body, and the air inlet is connected to a gas tank; the liquid inlet is connected to a waste hydrochloric acid pool; and a discharge port is provided at the bottom of the tank body.

[0024] Technical effect: This scheme adopts the above-mentioned setting, which makes it easy to pump waste hydrochloric acid and oxygen into the tank body, and discharge the produced ferric chloride solution for subsequent treatment to obtain a water treatment agent product.

[0025] Preferably, as an improvement, a graphite inlet is provided on the top of the tank body, a graphite outlet is provided on the bottom of the tank body, and a graphite heat exchanger pump and a graphite heat exchanger are connected via a pipeline between the graphite inlet and the graphite outlet.

[0026] Technical effect: The catalytic oxidation reaction of this scheme is an exothermic reaction, and the reaction can be started under normal temperature conditions. As the reaction releases heat, the temperature in the tank will gradually rise. This scheme adopts the above-mentioned setting, which is convenient for the graphite heat exchanger pump to extract the waste hydrochloric acid from the graphite outlet and pump it into the graphite heat exchanger. After heat exchange, it re-enters the tank through the graphite inlet, thereby cooling the waste hydrochloric acid, ensuring that the catalytic oxidation proceeds quickly while avoiding excessive temperature damage to the equipment. Specifically, the start-stop control method of the graphite heat exchanger is: when the temperature of the reaction liquid in the tank is 72-73°C, the graphite heat exchanger pump is turned on, and the reaction solution enters the graphite heat exchanger for heat exchange and cooling before returning to the tank; when the temperature drops to 68-70°C, the graphite heat exchanger pump is turned off and the heat exchange is suspended; after the temperature rises, the heat exchange is started again. By repeating this process, the temperature of the reaction liquid can be controlled to be lower than 75°C, effectively avoiding high temperature damage to the equipment; the temperature of the reaction liquid can also be controlled to be at a temperature reaction of rapid reaction, thereby improving the reaction efficiency.

[0027] Preferably, as an improvement, the top of the tank body is also provided with an auxiliary material hole, a liquid alkali and tap water inlet hole, an air intake hole, a manhole, an observation mirror arranged on the manhole, a one-way air intake valve, a remote pressure gauge, a bursting disc, a remote thermometer, a pressure relief valve, a feed port and an exhaust hole located in the middle of the top of the tank body.

[0028] Technical effect: This scheme adopts the above-mentioned settings to ensure the smooth operation of the tank. Specifically, the liquid alkali and tap water inlet holes are convenient for pumping in liquid alkali and tap water from the outside. Liquid alkali is used to adjust the alkalinity, and tap water is used to adjust the total iron content in the waste hydrochloric acid in the tank according to demand and production progress. The one-way suction valve is used to prevent negative pressure from being generated inside the tank during discharge to prevent the glass bottle from breaking. The auxiliary material hole is convenient for adding auxiliary materials such as catalysts to increase the reaction rate. The suction hole is connected to the suction pipe, which facilitates the oxygen in the tank to enter the ejector and react with the waste hydrochloric acid, thereby accelerating the reaction rate. The observation mirror is used for the operator to observe the changes in the material in the tank, so as to facilitate the real-time adjustment of the working conditions according to the changes in the situation and improve the reaction effect. The remote thermometer is used to monitor the temperature changes in the tank. The remote pressure gauge is used to monitor the pressure in the tank. The bursting disc can form a port for forced pressure relief when the pressure in the tank is uncontrolled, and the pressure relief valve is used to adjust the internal pressure of the tank when necessary. Both are protective devices when the pressure in the tank is too high. The tail gas hole is connected to the tail gas treatment device, which is used to output the tail gas generated by the reaction in the tank to prevent the tail gas from accumulating in the tank and affecting the reaction rate. The manhole makes it easy for workers to enter and exit the tank when maintenance is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a front view of the catalytic oxidation tank in an embodiment of the present invention.

[0030] Figure 2 It is a top view of the catalytic oxidation tank in an embodiment of the present invention.

[0031] Figure 3 It is a schematic diagram of the connection structure of the ejector and the acceleration reactor of the catalytic oxidation tank in an embodiment of the present invention.

[0032] Figure 4 This is a production site status diagram of the catalytic oxidation tank in an embodiment of the present invention.

[0033] Figure 5 This is a production site status diagram of a remote instrument in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following examples and experimental examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used can be obtained from commercial sources.

[0035] The marks in the drawings of the specification include: circulating pump 1, feed pipe 2, tank body 3, discharge pipe 4, ejector 5, suction pipe 6, manhole 7, air inlet 8, auxiliary material hole 9, ejector installation port 10, liquid inlet 11, suction hole 12, observation mirror 13, remote thermometer 14, solid material addition port 15, bursting disc 16, pressure relief valve 17, tail gas hole 18, liquid alkali and tap water inlet hole 19, remote pressure gauge 20, graphite inlet 21, graphite outlet 22, one-way suction valve 23.

[0036] Example

[0037] This solution provides a method for treating iron-containing waste hydrochloric acid, comprising the following steps:

[0038] (i) In the conditioning stage, waste hydrochloric acid containing iron from different sources is mixed, the iron content is adjusted according to production requirements, and the waste hydrochloric acid containing iron is filtered through a plate and frame;

[0039] As a reference, iron-containing waste hydrochloric acid from different sources is tempered into three types of solutions. The total iron content in the first type of solution is ≥15.6%, which is used to produce ferric chloride; the total iron content in the second type of solution is 12% to 15.6%, which is used to produce polyferric chloride water treatment agent; the total iron content in the third type of solution is 8% to 12%, which is used to produce ferric chloride water treatment agent with a ferric chloride content higher than 8%, or is mixed with the second type of solution to prepare a raw material with a total iron content of >12% for use in the production of polyferric chloride water treatment agent.

[0040] (ii) Catalytic oxidation stage: adding a catalyst to the waste hydrochloric acid containing iron, controlling the temperature to be below 75°C, introducing oxygen to control the pressure to be 0.02-0.03 MPa, reacting for 3-4 hours to oxidize the divalent iron ions in the waste hydrochloric acid to trivalent iron ions, and obtaining a reaction solution;

[0041] As a reference, the catalyst is sodium nitrite, and the amount of catalyst added is 2-3‰ of the total weight of iron-containing waste hydrochloric acid. The end point of catalytic oxidation is that the pressure rises and stabilizes for 5-10 minutes. The reaction is stopped when the ferrous ion content in the waste hydrochloric acid meets the requirements: when producing polyferric chloride, the ferrous ion content is controlled to be ≤0.2%; when producing ferric chloride, the ferrous ion content is controlled to be ≤0.1%.

[0042] As an improvement, the catalytic oxidation stage in this solution is completed in the catalytic oxidation tank. This solution also provides a catalytic oxidation tank, including a tank body 3, a circulation unit connected to the tank body 3, an ejector 5 connected between the tank body 3 and the circulation unit, and an acceleration reactor connected to the lower part of the ejector 5, and the acceleration reactor is located in the tank body 3.

[0043] like Figure 1 As shown, the circulation unit includes a discharge pipe 4 connected to the bottom of the tank body 3, a circulation pump 1 connected to the discharge pipe 4, a feed pipe 2 connected between the circulation pump 1 and the ejector 5, and an output pipe 18 connected to the feed pipe 2. A plurality of circulation pumps 1 can be provided. In this embodiment, the number of circulation pumps is specifically two, which are symmetrically arranged on the left and right sides of the tank body 3. Valves (not shown in the figure) are provided on the feed pipe 2 and the output pipe 18. The circulation unit also includes a graphite heat exchanger, such as Figure 2 As shown, a graphite inlet 21 is provided at the top of the tank body 3. Figure 1 As shown, a graphite outlet 22 is provided at the bottom of the tank body 3, and a graphite heat exchanger is connected between the graphite inlet 21 and the graphite outlet 22 (not shown in the figure). The material is pumped into the graphite heat exchanger from the graphite outlet 22 through the graphite heat exchanger pump, and then re-enters the tank body 3 through the graphite inlet 21, thereby cooling the material for heat exchange and temperature reduction.

[0044] The circulation pump 1 in the circulation unit can extract the waste hydrochloric acid in the tank body 3 and send it to the ejector 5 from the top of the tank body 3. When it is ejected into the tank body 3 through the ejector 5, it reacts with oxygen to accelerate the reaction, and then returns to the tank body 3 to replenish and accelerate the circulation of the waste hydrochloric acid, thereby accelerating the reaction rate. Figure 3As shown, the ejector 5 is located at the top of the tank body 3, and the top of the tank body 3 is provided with an ejector installation port 10 connected to the inside of the tank body 3, and the ejector installation port 10 is used to fix the ejector 5. The feed pipe 2 is connected to the ejector 5 from the top, and the mouth of the feed pipe 2 extends into the ejector 5. The side wall of the ejector 5 is provided with an intake pipe 6 connected to the inner cavity of the tank body 3, and a single-phase intake valve is provided in the intake pipe 6. The bottom of the ejector 5 is connected with an acceleration reactor, and the acceleration reactor includes an integrally formed straight pipe and a bent pipe. The straight pipe part is fixed with an inverted cone pipe, and the mouth of the inverted cone pipe is in the shape of an inverted cone; a plurality of bent pipes are provided, which are evenly distributed around the straight pipe in a circular direction with the straight pipe as the circumference, and the mouth of the bent pipe is upwardly tilted. The waste hydrochloric acid ejected from the ejector 5 is sprayed onto the inner wall of the inverted cone tube, and the shape of the inverted cone tube can once again play a role in collecting and pressurizing the waste hydrochloric acid, so that the waste hydrochloric acid is accelerated to flow out of the ejector 5, so that the gas inside the ejector 5 is quickly rushed out and becomes a negative pressure state, so that the oxygen in the tank body 3 can be quickly sucked into the ejector 5 along the suction pipe 6 to react with the waste hydrochloric acid, thereby accelerating the speed of oxygen entering the ejector 5 and improving the reaction efficiency. A bend is set under the straight pipe, so that after the waste hydrochloric acid flows into the straight pipe, it can flow to the pipe mouth along the arc inner wall of the bend. On the one hand, it can improve the smoothness of the waste hydrochloric acid flowing out of the bend, speed up the flow rate of the waste hydrochloric acid, and improve the efficiency; on the other hand, the pipe mouth of the bend is tilted upward, so that the waste hydrochloric acid has an upward trend after being ejected, so that it can have a positive contact with the oxygen introduced from the top of the tank body 3, thereby increasing the contact area between the waste hydrochloric acid and the oxygen, and further improving the reaction rate.

[0045] like Figure 2 As shown, the top of the tank body 3 is also provided with an auxiliary material hole 9, a liquid alkali and tap water inlet hole 19, an air inlet 8, an air suction hole 12, a manhole 7, an observation mirror 13 arranged on the manhole 7, a one-way air suction valve 23, a remote pressure gauge 20, a bursting disc 16, a remote thermometer 14, a pressure relief valve 17, a solid material addition port 15, a liquid inlet 11 and an exhaust hole 18 located in the middle of the top of the tank body 3.

[0046] Among them, the air inlet 8 is used to introduce oxygen into the tank body 3. The liquid alkali and tap water inlet hole 19 is convenient for pumping liquid alkali and tap water from the outside. The liquid alkali is used to adjust the basicity, and the tap water is used to adjust the iron content according to demand. The one-way air intake valve 23 is used to prevent the negative pressure from being generated inside the tank body 3 during discharge, so as to prevent the tank body 3 from rupturing. The auxiliary material hole 9 is convenient for adding auxiliary materials such as catalysts to increase the reaction speed. The liquid inlet 11 is convenient for sending waste hydrochloric acid into the tank body 3. The air intake hole 12 is connected to the air intake pipe 6, which is convenient for the oxygen in the tank body 3 to enter the ejector 5 and react with the waste hydrochloric acid, thereby accelerating the reaction rate. The observation mirror 13 is used for the operator to observe the changes in the materials in the reactor, so as to adjust the working conditions according to the changes and improve the reaction effect. The remote thermometer 14 is used to monitor the temperature changes in the tank body 3. The remote pressure gauge 20 is used to monitor the pressure in the tank body 3. The bursting disc 16 can release the pressure by bursting to form a port when the pressure in the tank body 3 is out of control, and the pressure relief valve 17 is used to adjust the internal pressure of the tank body 3 when necessary. Both are protective devices when the pressure in the tank body 3 is too high. The tail gas hole 18 is connected to the tail gas treatment device, which is used to output the tail gas obtained after the reaction in the tank body 3 to prevent the tail gas from accumulating in the tank body 3 and affecting the reaction rate. The setting of the manhole 7 makes it convenient for the staff to enter and exit when the tank body 3 needs maintenance.

[0047] The working process of the catalytic oxidation tank in this scheme is as follows:

[0048] ① The quenched and tempered iron-containing waste hydrochloric acid is injected into the tank body 3 through the liquid inlet 11, and oxygen is introduced into the tank body 3 through the air inlet 8.

[0049] ② Start the circulation pump 1, pump the waste hydrochloric acid into the ejector 5 through the circulation pump, and then spray it into the tank body 3 through the ejector 5. A vacuum is formed inside the ejector 5, so that the oxygen in the tank body 3 can be sucked into the ejector 5 through the suction pipe 6 to react with the divalent iron in the waste hydrochloric acid and oxidize it into trivalent iron.

[0050] ③ The sodium nitrite solution is injected into the tank body 3 through the auxiliary material hole 9.

[0051] ④ Open the oxygen valve, and oxygen enters the tank body 3 from the oxygen inlet hole 8.

[0052] ⑤ Adjust the pressure in the tank 3 and control the pressure at 0.02Mpa (optionally 0.02-0.03MPa).

[0053] The pressure control of this scheme is used to ensure the amount of oxygen, that is, the pressure is limited to 0.02-0.03 MPa, which can meet the required amount of oxygen. After the reaction is completed, the pressure continues to rise and no longer drops. After entering the pressure holding state for 5-10 minutes, the divalent iron content is sampled and tested. When the divalent iron content is qualified (that is, when producing polyferric chloride, the ferrous ion content is controlled to be ≤0.2%; when producing ferric chloride, the ferrous ion content is controlled to be ≤0.1%), it means that the oxidation is complete and the reaction can be stopped.

[0054] ⑥ When the temperature inside the tank body 3 reaches 72-73°C, start the circulating cooling water system to keep the temperature inside the tank body 3 not exceeding 75°C.

[0055] ⑦React for 3 hours (optionally 3 to 4 hours) to completely oxidize the divalent iron in the waste hydrochloric acid into trivalent iron.

[0056] ⑧Open the valve on the output pipe and the valve of the tail gas hole 18, close the valve of the feed pipe 2, so that the completely oxidized reaction solution is transferred to the product temporary storage tank through the circulation pump 1 for aging for 24 hours, and the tail gas enters the tail gas system through the tail gas hole 18 for treatment and discharge after meeting the standards.

[0057] (III) Post-treatment stage: After aging, the reaction solution is transferred to a product tank for storage to obtain ferric chloride liquid.

[0058] This solution optimizes catalytic oxidation, effectively shortens batch processing time and improves production efficiency while ensuring oxidation effect. Specifically, when this solution actually uses catalytic oxidation to treat iron-containing waste hydrochloric acid to produce ferric chloride water treatment agent, the product yield can reach 11-12t / 8h (3-4h for catalytic oxidation, and the rest of the time for feeding, discharging, etc.), and three batches can be produced every day, making the ferric chloride water treatment agent product yield as high as 35-36t / d, significantly improving production efficiency.

[0059] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for treating iron-containing waste hydrochloric acid, characterized in that: The method comprises the following steps: (i) a conditioning stage, mixing iron-containing waste hydrochloric acid from different sources, adjusting the iron content according to production requirements and filtering the iron-containing waste hydrochloric acid through a plate and frame; (ii) a catalytic oxidation stage, adding a catalyst to the iron-containing waste hydrochloric acid, controlling the temperature to be below 75° C., introducing oxygen to control the pressure to be 0.02 to 0.03 MPa, reacting for 3 to 4 hours to oxidize the divalent iron ions in the waste hydrochloric acid into trivalent iron ions, and obtaining a reaction solution; (iii) a post-treatment stage: the reaction solution is subjected to the salt base adjustment by adding liquid alkali to obtain ferric chloride or polyferric chloride liquid.

2. The method for treating waste iron-containing hydrochloric acid according to claim 1, characterized in that: In the (i) conditioning stage, the iron-containing waste hydrochloric acid from different sources is conditioned into three types of solutions. The first type of solution has a total iron content of ≥15.6% and is used to produce ferric chloride; the second type of solution has a total iron content of 12% to 15.6% and is used to produce polyferric chloride water treatment agent; the third type of solution has a total iron content of 8% to 12% and is used to produce polyferric chloride water treatment agent with a polyferric chloride content higher than 8%, or is mixed with the second type of solution to prepare a raw material with a total iron content of >12% for use in the production of polyferric chloride water treatment agent.

3. The method for treating waste iron-containing hydrochloric acid according to claim 1, characterized in that: In the (ii) catalytic oxidation stage, the catalyst is sodium nitrite, and the amount of catalyst added is 2-3‰ of the total weight of the iron-containing waste hydrochloric acid.

4. The method for treating waste hydrochloric acid containing iron according to claim 1, characterized in that: In the (ii) catalytic oxidation stage, the endpoint of the catalytic oxidation is that the pressure rises and stabilizes for 5 to 10 minutes, and the reaction is stopped when the ferrous ion content in the waste hydrochloric acid meets the requirements: when producing polyferric chloride, the ferrous ion content is controlled to be ≤0.2%; when producing ferric chloride, the ferrous ion content is controlled to be ≤0.1%.

5. The method for treating iron-containing waste hydrochloric acid according to claim 1, characterized in that: In the (ii) catalytic oxidation stage, the catalytic oxidation is completed in a catalytic oxidation tank, which includes a tank body, a circulation unit connected to the tank body, an ejector connected between the tank body and the circulation unit, and an acceleration reactor connected to the lower part of the ejector, wherein the acceleration reactor is located in the tank body; an intake pipe connected to the tank body is provided on the side of the ejector, and a one-way valve is provided on the intake pipe.

6. The method for treating waste hydrochloric acid containing iron according to claim 5, characterized in that: The accelerating reactor comprises an integrally formed straight tube and a bent tube, wherein an inverted cone tube is fixed to the straight tube, and the mouth of the inverted cone tube is in the shape of an inverted cone; a plurality of bent tubes are arranged, which are evenly distributed around the straight tube in a circular direction, and the mouths of the bent tubes are tilted upwards.

7. The method for treating waste hydrochloric acid containing iron according to claim 5, characterized in that: The circulation unit includes a discharge pipe connected to the bottom of the tank body, a circulation pump connected to the discharge pipe, a feed pipe connected between the circulation pump and the ejector, and an output pipe connected to the feed pipe. Multiple circulation pumps can be provided, and valves are provided on the feed pipe and the output pipe.

8. The method for treating waste hydrochloric acid containing iron according to claim 5, characterized in that: The top of the tank body is provided with a liquid inlet and an air inlet, the air inlet is connected with a gas tank; the liquid inlet is connected with a waste hydrochloric acid pool; and the bottom of the tank body is provided with a discharge port.

9. The method for treating waste hydrochloric acid containing iron according to claim 5, characterized in that: A graphite inlet is arranged on the top of the tank body, a graphite outlet is arranged on the bottom of the tank body, and a graphite heat exchanger pump and a graphite heat exchanger are connected through a pipeline between the graphite inlet and the graphite outlet.

10. The method for treating waste hydrochloric acid containing iron according to claim 5, characterized in that: The top of the tank body is also provided with auxiliary material holes, liquid alkali and tap water inlet holes, air intake holes, manholes, an observation mirror arranged on the manhole, a one-way air intake valve, a remote pressure gauge, a bursting disc, a remote thermometer, a pressure relief valve, a feed port and an exhaust hole located in the middle of the top of the tank body.

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