Iron-containing spent hydrochloric acid treatment regeneration apparatus and method

Abstract

The application provides a kind of iron-containing waste hydrochloric acid treatment regeneration equipment and method, and relates to the technical field of waste acid resource treatment.The iron-containing waste hydrochloric acid treatment regeneration equipment of the application includes a hydrochloric acid evaporation regeneration unit, a waste liquid impurity removal unit and a regenerated composite flocculant preparation unit.The application realizes the recovery of waste hydrochloric acid, the reduction and removal of hexavalent chromium and the preparation of regenerated composite flocculant, and has multiple advantages of resource recycling and efficient removal of pollutants.

Description

Technical Field

[0001] This invention relates to the field of waste acid resource utilization technology, specifically to a waste hydrochloric acid treatment and regeneration equipment and method containing iron. Background Technology

[0002] Iron-containing waste hydrochloric acid is a common waste liquid in industries such as electroplating, leather, and chemicals. It mainly originates from processes such as pickling, etching, and neutralization, and is characterized by high acidity, high iron content, and heavy metal pollution. This type of waste hydrochloric acid typically contains iron ions (Fe²⁺). ⁺ Hexavalent chromium (or Fe³⁺) and heavy metal chromium ions, among others, is highly toxic and carcinogenic. Its high mobility exacerbates environmental pollution problems, making its removal a crucial research area in water treatment. Traditional chromium removal methods include chemical reduction, adsorption, and biodegradation; however, these methods suffer from slow reaction rates, complex operations, and high costs in practical applications.

[0003] The main methods for recovering and utilizing iron-containing waste hydrochloric acid include neutralization, direct roasting, extraction, evaporation concentration, and membrane separation (diffusion dialysis, electrodialysis, airlift membrane filtration, etc.). Traditional neutralization methods, due to their high cost and difficulty in disposing of precipitated sludge, have been largely phased out by most enterprises. High-temperature roasting, despite its high economic value in recovering hydrochloric acid and iron oxide powder, is only industrially applied by large steel companies due to its large initial investment and stringent equipment and process requirements. Evaporation crystallization methods result in residual iron content in the effluent that fails to meet standards. Ion exchange and membrane treatment methods are limited by high iron concentrations and are prone to resin and membrane fouling. The market capacity for products from evaporation distillation methods is small, and product quality is difficult to guarantee.

[0004] In conclusion, given the current severe situation regarding the treatment of iron-containing waste hydrochloric acid, it is imperative to develop new equipment and methods for treating and regenerating iron-containing waste hydrochloric acid that can achieve waste hydrochloric acid recovery, efficient removal of pollutants, and resource recycling. Summary of the Invention

[0005] The purpose of this invention is to provide an equipment and method for treating and regenerating iron-containing waste hydrochloric acid, so as to solve the problems mentioned in the background art.

[0006] In a first aspect, the present invention provides a method for treating and regenerating iron-containing waste hydrochloric acid, comprising:

[0007] S1: Iron-containing waste hydrochloric acid is evaporated by a multi-effect evaporator. The volatilized HCl gas is absorbed by a water absorption tower to form regenerated hydrochloric acid. The tail gas at the top of the water absorption tower is treated by an alkaline absorption tower.

[0008] S2: The liquid material after being processed by the multi-effect evaporator is sent into the reactor. Modified bentonite-loaded nano-zero-valent iron is added to the reactor for reduction reaction. Then, alkaline solution is added to adjust the pH. Next, regenerated composite flocculant is added for precipitation reaction. Solid-liquid separation yields the first filter cake and filtrate.

[0009] S3: Add the regenerated hydrochloric acid from step S1 to the filtrate from step S2 to adjust the pH, then add polyferric chloride, nano-bentonite and oxidant to react, and the resulting product is subjected to solid-liquid separation to obtain regenerated composite flocculant and second filter cake.

[0010] In a preferred embodiment of the present invention, in S1, the volatilized HCl gas is sent to the water absorption tower after exchanging heat with cooling water at 20-30°C in the first heat exchanger. The evaporation treatment temperature is 80-100°C. After heat exchange in the first heat exchanger, the temperature of the HCl gas is 40-60°C. The regenerated hydrochloric acid obtained after absorption in the water absorption tower has a concentration of 10-20 wt% and is sent to the regenerated hydrochloric acid storage tank. The alkaline absorption tower uses a 5-10 wt% NaOH solution with a spray density of 10-20 m³ / (m²·h).

[0011] In a preferred embodiment of the present invention, in S2, the liquid material processed by the multi-effect evaporator is sent to the second heat exchanger, and the cooling water flowing out of the first heat exchanger is sent to the second heat exchanger. After heat exchange, the liquid material is sent to the reactor. The temperature of the liquid material after heat exchange in the second heat exchanger is 60-80°C.

[0012] In a preferred embodiment of the present invention, in S1, the iron-containing waste hydrochloric acid is sent to the third heat exchanger for heat exchange and then to the multi-effect evaporator. The cooling water flowing out of the second heat exchanger is sent to the third heat exchanger to exchange heat with the iron-containing waste hydrochloric acid.

[0013] In a preferred embodiment of the present invention, in S2, the method for preparing the modified bentonite-supported nano-zero-valent iron is as follows:

[0014] (1) First grind the bentonite through a 200-mesh sieve, then wash it with deionized water and dry it;

[0015] (2) Mix bentonite and CTAB at a weight ratio of 20:1, stir and react at 60-80℃ for 2-4 hours. After the reaction is completed, wash with deionized water until there is no CTAB residue, dry, and pulverize to a particle size of 1-100nm to obtain nano-sized modified bentonite.

[0016] (3) Disperse nano-sized modified bentonite in deionized water to form a modified bentonite suspension; add nano-zero valent iron particles with a purity ≥99% and a particle size of 100-200 mesh to the modified bentonite suspension, with a mass ratio of nano-zero valent iron particles to modified bentonite of 1:10, stir and react for 1-2 hours, separate the solid and liquid, and dry the solid product under nitrogen protection to obtain nano-zero valent iron supported on modified bentonite.

[0017] In a preferred embodiment of the present invention, in S2, the amount of modified bentonite-supported nano-zero valent iron added is 5-30 g / L.

[0018] In a preferred embodiment of the present invention, in step S2, an alkaline solution is added to adjust the pH to 7-9, and the dosage of the regenerated composite flocculant is 10-50 mg / L.

[0019] In a preferred embodiment of the present invention, in step S3, regenerated hydrochloric acid is added to adjust the pH to 4-5, the dosage of polyferric chloride is 10-50 mg / L, the particle size of nano-bentonite is 1-100 nm and the dosage is 1-5 g / L, and the oxidant is 30 wt% hydrogen peroxide and the dosage is 0.1-0.5 g / L.

[0020] Secondly, the present invention provides an iron-containing waste hydrochloric acid treatment and regeneration device, comprising:

[0021] The hydrochloric acid evaporation and regeneration unit includes a multi-effect evaporator, a water absorption tower, and an alkali absorption tower connected in sequence by pipelines. The upper part of the alkali absorption tower is connected to an alkali storage tank by a pipeline, and the lower part is connected to a tail liquid tank by a pipeline. The lower part of the water absorption tower is connected to a regenerated hydrochloric acid storage tank by a pipeline.

[0022] The waste liquid removal unit includes a reaction vessel, a first pH adjustment tank, a flocculation reaction tank, and a first solid-liquid separation device connected in sequence by pipes. The upper part of the reaction vessel is connected by a pipe to a reducing agent storage tank for storing nano-zero-valent iron loaded with modified bentonite. The lower part of the multi-effect evaporator is connected to the reaction vessel by a pipe. The first pH adjustment tank is connected to an alkaline solution storage tank by a pipe. The flocculation reaction tank is connected to a regenerated composite flocculant storage tank by a pipe. The solid material outlet of the first solid-liquid separation device discharges the first filter cake.

[0023] The regenerated composite flocculant preparation unit includes a second pH adjustment tank, a mixing reaction tank, and a second solid-liquid separation device connected in sequence by pipelines. The upper part of the second pH adjustment tank is connected to the regenerated hydrochloric acid storage tank and the outlet of the first solid-liquid separation device, respectively. The lower part of the second pH adjustment tank is connected to the mixing reaction tank. The upper part of the mixing reaction tank is also connected to a polyferric chloride feeding device, a nano-bentonite feeding device, and an oxidant feeding device, respectively. The outlet of the second solid-liquid separation device is connected to the regenerated composite flocculant storage tank, and the solid material outlet of the second solid-liquid separation device discharges the second filter cake.

[0024] In a preferred embodiment of the present invention, a first heat exchanger is provided between the multi-effect evaporator and the water absorption tower, a second heat exchanger is provided between the multi-effect evaporator and the reaction vessel, and a third heat exchanger is provided on the pipeline for inputting iron-containing waste hydrochloric acid into the multi-effect evaporator. External circulating cooling water flows through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence via the water supply pipeline and then flows back into the return water pipe.

[0025] In a preferred embodiment of the present invention, a branch pipe is provided on the pipeline between the third heat exchanger and the return water pipe, and the branch pipe is connected to the water absorption tower.

[0026] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0027] This invention achieves the recovery of waste hydrochloric acid, the reduction and removal of hexavalent chromium, and the preparation of a regenerated composite flocculant, offering multiple advantages such as resource recycling and efficient pollutant removal. The multi-effect evaporator, first heat exchanger, second heat exchanger, and third heat exchanger improve thermal energy utilization efficiency and reduce energy consumption during evaporation, while also achieving high HCl recovery and stable operation. By recovering hydrochloric acid and preparing and recycling the regenerated composite flocculant, raw material costs are reduced. The regenerated composite flocculant possesses flocculation, adsorption, and oxidation functions, making it a multifunctional water treatment agent suitable for wastewater treatment. The resulting first and second filter cakes are rich in chromium and iron, and after centralized collection, they are easily treated through harmless or resource-based utilization, reducing waste emissions. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a waste hydrochloric acid treatment and regeneration device containing iron, as described in Example 1.

[0029] Figure 2 The graph shows the effect of the amount of nano-zero valent iron loaded with modified bentonite on the removal rate of Cr(VI) in Experiment Example 1.

[0030] Figure 3 This is a line graph showing the effect of different initial pH values ​​of waste acid on the Cr(VI) removal rate in Experiment Example 2.

[0031] Figure 4 This is a line graph showing the effect of different stirring rates on chromium removal efficiency in Experiment Example 5.

[0032] Figure labels: 1-Multi-effect evaporator, 2-Water absorption tower, 3-Reaction vessel, 4-First heat exchanger, 5-Second heat exchanger, 6-Third heat exchanger, 7-Alkali absorption tower, 8-Alkali storage tank, 9-Regenerated hydrochloric acid storage tank, 10-Tail liquid tank, 11-Reducing agent storage tank, 12-First pH adjustment tank, 13-Flocculation reaction tank, 14-First solid-liquid separation device, 15-Regenerated composite flocculant storage tank, 16-Second pH adjustment tank, 17-Polyferric chloride feeding device, 18-Nano bentonite feeding device, 19-Oxidant feeding device, 20-Mixed reaction tank, 21-Second solid-liquid separation device. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Example

[0034] Please see the appendix Figure 1 As shown, an iron-containing waste hydrochloric acid treatment and regeneration device according to this embodiment includes:

[0035] The hydrochloric acid evaporation and regeneration unit includes a multi-effect evaporator 1, a water absorption tower 2, and an alkaline absorption tower 7 connected in sequence by pipes. The upper part of the alkaline absorption tower 7 is connected to an alkaline storage tank 8 by pipes, and the lower part is connected to a tail liquid tank 10 by pipes. The lower part of the water absorption tower 2 is connected to a regenerated hydrochloric acid storage tank 9 by pipes.

[0036] The waste liquid removal unit includes a reaction vessel 3, a first pH adjustment tank 12, a flocculation reaction tank 13, and a first solid-liquid separation device 14 connected in sequence by pipes. The upper part of the reaction vessel 3 is connected by a pipe to a reducing agent storage tank 11 for storing nano-zero valent iron loaded with modified bentonite. The lower part of the multi-effect evaporator 1 is connected to the reaction vessel 3 by a pipe. The first pH adjustment tank 12 is connected by a pipe to an alkaline storage tank 8. The flocculation reaction tank 13 is connected by a pipe to a regenerated composite flocculant storage tank 15. The first filter cake is discharged from the solid material outlet of the first solid-liquid separation device 14.

[0037] The regenerated composite flocculant preparation unit includes a second pH adjustment tank 16, a mixing reaction tank 20, and a second solid-liquid separation device 21 connected in sequence by pipes. The upper part of the second pH adjustment tank 16 is connected to the regenerated hydrochloric acid storage tank 9 and the outlet of the first solid-liquid separation device 14, respectively. The lower part of the second pH adjustment tank 16 is connected to the mixing reaction tank 20. The upper part of the mixing reaction tank 20 is also connected to a polyferric chloride feeding device 17, a nano-bentonite feeding device 18, and an oxidant feeding device 19, respectively. The outlet of the second solid-liquid separation device 21 is connected to the regenerated composite flocculant storage tank 15, and the solid material outlet of the second solid-liquid separation device 21 discharges the second filter cake.

[0038] In this embodiment, iron-containing waste hydrochloric acid enters a multi-effect evaporator 1, where it is heated to evaporate HCl gas. The HCl gas then enters a water absorption tower 2 to generate regenerated hydrochloric acid, while the unabsorbed HCl gas enters an alkaline absorption tower 7 to generate NaCl solution. The concentrated waste liquid discharged from the multi-effect evaporator 1 enters a reaction vessel 3, where it reacts with nano-zero-valent iron supported by modified bentonite. 6 ⁺ is reduced to Cr³⁺, and then the waste liquid enters the first pH adjustment tank 12, where alkali is added to adjust the pH, generating Cr(OH)₃ precipitate. The waste liquid then enters the flocculation reaction tank 13, where regenerated composite flocculant is added to promote flocculation. The flocculated waste liquid enters the first solid-liquid separation device 14 to separate the supernatant and precipitate. The supernatant discharged from the first solid-liquid separation device 14 enters the second pH adjustment tank 16, where regenerated hydrochloric acid is added to adjust the pH. The waste liquid enters the mixing reaction tank 20, where polyferric chloride, nano-bentonite, and an oxidant are added to prepare a regenerated composite flocculant. The liquid regenerated composite flocculant enters the regenerated composite flocculant storage tank 15 for use in the waste liquid impurity removal unit.

[0039] Specifically, a first heat exchanger 4 is provided between the multi-effect evaporator 1 and the water absorption tower 2, a second heat exchanger 5 is provided between the multi-effect evaporator 1 and the reaction vessel 3, and a third heat exchanger 6 is provided on the pipeline into which the iron-containing waste hydrochloric acid is input to the multi-effect evaporator 1. External circulating cooling water flows sequentially through the first heat exchanger 4, the second heat exchanger 5, and the third heat exchanger 6 via the water supply pipeline and then flows back into the return water pipe. A branch pipeline is provided on the pipeline between the third heat exchanger 6 and the return water pipe, and this branch pipeline is connected to the water absorption tower 2. A heat exchange system is formed by the first heat exchanger 4, the second heat exchanger 5, and the third heat exchanger 6, which improves the thermal energy utilization efficiency of the hydrochloric acid evaporation and regeneration unit and reduces the energy consumption of the evaporation process. Example

[0040] Based on Example 1, this example provides a method for treating and regenerating iron-containing waste hydrochloric acid, the specific steps of which include:

[0041] S1: Iron-containing waste hydrochloric acid is evaporated by a multi-effect evaporator. The volatilized HCl gas is absorbed by a water absorption tower to form regenerated hydrochloric acid. The tail gas at the top of the water absorption tower is treated by an alkaline absorption tower.

[0042] S2: The liquid material after being processed by the multi-effect evaporator is sent into the reactor. Modified bentonite-loaded nano-zero-valent iron is added to the reactor for reduction reaction. Then, alkaline solution is added to adjust the pH. Next, regenerated composite flocculant is added for precipitation reaction. Solid-liquid separation yields the first filter cake and filtrate.

[0043] S3: Add the regenerated hydrochloric acid from step S1 to the filtrate from step S2 to adjust the pH, then add polyferric chloride, nano-bentonite and oxidant to react, and the resulting product is subjected to solid-liquid separation to obtain regenerated composite flocculant and second filter cake.

[0044] In this embodiment, the volatilized HCl gas is exchanged with cooling water at 20-30°C in a first heat exchanger before being sent to the water absorption tower. The evaporation temperature is 80-100°C. After heat exchange in the first heat exchanger, the HCl gas temperature is 40-60°C. The regenerated hydrochloric acid obtained after absorption in the water absorption tower has a concentration of 10-20 wt% and is sent to the regenerated hydrochloric acid storage tank. The alkali absorption tower uses a 5-10 wt% NaOH solution with a spray density of 10-20 m³ / (m²·h). The first heat exchanger reduces the temperature of the HCl gas while simultaneously reducing the heat load on the water absorption tower. The cooled HCl gas enters the water absorption tower and comes into countercurrent contact with the water inside. Both the water absorption tower and the alkali absorption tower are packed towers or spray towers to improve gas-liquid contact efficiency.

[0045] In this embodiment, the liquid material treated by the multi-effect evaporator is fed into the second heat exchanger, and the cooling water flowing out of the first heat exchanger is also fed into the second heat exchanger. After heat exchange, the liquid material is then fed into the reactor. The temperature of the liquid material after heat exchange in the second heat exchanger is 60-80℃. The liquid material treated by the multi-effect evaporator is cooled by the second heat exchanger, which reduces the heat load on the reactor and keeps the liquid material at a suitable reaction temperature for the modified bentonite-supported nano-zero-valent iron. This avoids excessively high temperatures affecting the reactivity of the modified bentonite-supported nano-zero-valent iron and limiting the removal rate.

[0046] In this embodiment, the iron-containing waste hydrochloric acid is fed into the third heat exchanger for heat exchange before being sent to the multi-effect evaporator. The cooling water flowing out of the second heat exchanger is sent to the third heat exchanger to exchange heat with the iron-containing waste hydrochloric acid. The iron-containing waste hydrochloric acid is preheated by the third heat exchanger, reducing evaporation energy consumption.

[0047] Specifically, in S2, the dosage of modified bentonite-supported nano-zero ferric iron is 5-30 g / L, the pH is adjusted to 7-9 by adding alkaline solution, and the dosage of regenerated composite flocculant is 10-50 mg / L; in S3, the pH is adjusted to 4-5 by adding regenerated hydrochloric acid, the dosage of polyferric chloride is 10-50 mg / L, the particle size of nano-bentonite is 1-100 nm and the dosage is 1-5 g / L, and the oxidant is 30 wt% hydrogen peroxide and the dosage is 0.1-0.5 g / L.

[0048] In this embodiment, both the first and second solid-liquid separation devices are plate and frame filter presses with a controlled pressure of 0.2-0.5 MPa. The reaction vessel is equipped with a stirring mechanism with a stirring speed controlled at 100-500 rpm. When the reaction is carried out in the flocculation reaction tank, the stirring speed is controlled at 50-100 rpm and the flocculation time is 10-30 min. When the reaction is carried out in the mixing reaction tank, the stirring speed is controlled at 100-200 rpm.

[0049] In this embodiment, the first filter cake is composed of Cr(OH)3, Fe(OH)3, modified bentonite and other impurities, and the second filter cake is composed of Fe(OH)3, nano-bentonite, Cr(OH)3 and other impurities.

[0050] Because the solid impurities in the first and second filter cakes have certain similarities in composition and properties, they can be processed together for resource recovery. Iron resources are processed into Fe2O3 or Fe3O4 through high-temperature calcination or reduction calcination. Fe2O3 is used to prepare pigments, magnetic materials, or catalysts, while Fe3O4 is used to prepare magnetic materials or battery electrodes. Chromium resources are converted to Cr2O3 through oxidation, which is used to prepare pigments, catalysts, or refractory materials. Bentonite resources are recovered through acid washing or alkali washing methods. Bentonite can be reused for loading nZVI or as an adsorbent.

[0051] In this embodiment, the method for preparing the modified bentonite-supported nano-zero-valent iron is as follows:

[0052] (1) First grind the bentonite through a 200-mesh sieve, then wash it with deionized water and dry it;

[0053] (2) Mix bentonite and CTAB at a weight ratio of 20:1, stir and react at 60-80℃ for 2-4 hours. After the reaction is completed, wash with deionized water until there is no CTAB residue, dry, and pulverize to a particle size of 1-100nm to obtain nano-sized modified bentonite.

[0054] (3) Disperse nano-sized modified bentonite in deionized water to form a modified bentonite suspension; add nano-zero valent iron particles with a purity ≥99% and a particle size of 100-200 mesh to the modified bentonite suspension, with a mass ratio of nano-zero valent iron particles to modified bentonite of 1:10, stir and react for 1-2 hours, separate the solid and liquid, and dry the solid product under nitrogen protection to obtain nano-zero valent iron supported on modified bentonite.

[0055] The following experiments investigate the effects of the dosage of modified bentonite-loaded nano-zero-valent iron, the initial pH of the waste acid, the reaction time, the temperature, and the stirring rate on the chromium removal efficiency in this embodiment.

[0056] In the experiment, the Cr(VI) simulated waste acid solution was prepared with K2Cr2O7, and the initial Cr(VI) concentration was strictly controlled at 100 mg / L. The pH value was adjusted by 0.1 mol / L HCl or NaOH, and the range was set from 1 to 5.

[0057] Experimental Example 1: Effect of Modified Bentonite-Loaded Nano-Zero-Variant Iron Dosage on Chromium Removal Efficiency

[0058] The removal efficiency of modified bentonite-loaded nano-zero-valent iron (ZVI) on Cr(VI) in waste acid was evaluated using different dosages. The results are as follows: Figure 2 As shown in the figure, the removal rate of Cr(VI) significantly increased with increasing ZVI dosage: 45% at 5 g / L, 67.5% at 10 g / L, 82% at 15 g / L, reaching 90% at 20 g / L, and stabilizing at 91% at 25 g / L. This saturation phenomenon indicates that the reaction rate is limited as the active sites on the ZVI surface become saturated, and additional ZVI dosage no longer significantly improves the removal effect. Furthermore, excessive dosage leading to particle aggregation further reduces the effective specific surface area of ​​ZVI, affecting mass transfer efficiency. The experimental results are consistent with the Langmuir adsorption model, determining 20 g / L as the optimal dosage, achieving efficient Cr(VI) removal while avoiding excessive material usage.

[0059] Experimental Example 2: The Effect of Initial pH of Waste Acid on Chromium Removal Efficiency

[0060] The removal efficiency of Cr(VI) from waste acid with different pH values ​​ranging from 3 to 11 was evaluated. The results are as follows: Figure 3 As shown in the figure. The results indicate that the removal rate of Cr(VI) is highest under acidic conditions (pH 3 to 5), especially at pH 5, where the removal rate reaches 88.5%. At this point, the reaction between ZVI and Cr2O7²⁻ is most complete. The acidic environment promotes the corrosion reaction of ZVI and accelerates the reduction of Cr(VI), increasing the reaction rate and electron transfer efficiency. When the pH value increases to neutral and alkaline (pH 7 to 11), the removal efficiency decreases significantly. At pH 7, the removal rate is 70%, indicating that the removal capacity of ZVI begins to be limited by the passivation layer. As the pH further increases to 9 and 11, the removal rate decreases to 58% and 43%, respectively. Under alkaline conditions, the oxide layer formed on the ZVI surface significantly reduces the reduction reaction efficiency of Cr(VI), making it difficult for CrO4²⁻ to react effectively with ZVI at higher pH levels. During the experiment, the initial pH of the solution was precisely controlled using a Mettler Toledo pH meter, and the residual concentration of Cr(VI) was measured at a wavelength of 540 nm using a UV-Vis spectrophotometer to ensure the accuracy of the data.

[0061] Experimental Example 3: Effect of Reaction Time on Chromium Removal Efficiency

[0062] The effect of reaction time on the removal efficiency of Cr(VI) was investigated by setting different reaction times (15 min, 30 min, 60 min, 120 min, 180 min, and 240 min). The results showed that in the initial stage (0 to 60 min), the Cr(VI) removal rate increased rapidly, from 52% at 15 min to 82% at 60 min. This was mainly due to the large number of active sites on the ZVI surface in the early stage of the reaction, allowing for rapid reduction of Cr(VI). When the reaction time was extended to 120 min, the removal rate reached 90%, but the removal rate subsequently decreased significantly, with the removal rate only slightly increasing to 93% at 240 min, indicating that the reaction had approached equilibrium. By fitting the experimental data, the reaction process conformed to a pseudo-first-order kinetic model, and its kinetic equation is:

[0063] (1)

[0064] Where C0 is the initial Cr(VI) concentration, C is the Cr(VI) concentration at time t, kobs is the reaction rate constant, and t is the reaction time. According to data fitting, the reaction rate constant kobs value is relatively large within the initial 60 minutes, approximately 0.032 min⁻¹, indicating that the reduction of Cr(VI) in this stage is mainly controlled by diffusion mass transfer. With the extension of reaction time, surface passivation increases, leading to a reduction in effective reaction sites, limited mass transfer, and a gradual decrease in the reaction rate. The Cr(VI) concentration was determined using an Agilent Cary 60UV-Vis spectrophotometer at a wavelength of 540 nm via the diphenylcarbazide method to ensure measurement accuracy and data repeatability at each time point.

[0065] Experimental Example 4: Effect of Temperature on Chromium Removal Efficiency

[0066] Five different temperature conditions (10℃, 20℃, 30℃, 40℃, and 50℃) were set to investigate the effect of reaction time on the removal efficiency of Cr(VI). The results showed that the removal rate of Cr(VI) significantly increased with increasing temperature, reaching 65.2% at 10℃ and 87.4% at 30℃. This increase was attributed to the accelerated reaction rate and increased surface activity of zero-valent iron (ZVI) at higher temperatures. When the temperature reached 50℃, the removal rate plateaued, reaching 91.5%, indicating that the reaction was gradually approaching saturation. The reaction rate constant k was fitted using the Arrhenius equation.

[0067] (2)

[0068] Where A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the absolute temperature. According to the fitted data, the activation energy Ea for ZVI reduction of Cr(VI) is 28.6 kJ / mol, indicating that the reaction is temperature-sensitive and its rate is diffusion-controlled. The study also found that under high-temperature conditions, the formation rate of iron corrosion products and the passivation layer is accelerated, leading to a reduction in effective reaction sites and thus limiting further improvement in the removal rate. The experiment used a constant-temperature water bath to control the temperature, and a UV-Vis spectrophotometer was used to determine the residual concentration of Cr(VI) at different temperatures.

[0069] Experimental Example 5: Effect of stirring rate on chromium removal efficiency

[0070] This experiment used five different stirring rates: 100 rpm, 200 rpm, 300 rpm, 400 rpm, and 500 rpm, while keeping other experimental conditions constant (zero-valent iron dosage 20 g / L, initial Cr(VI) concentration 100 mg / L, pH 5, temperature 30℃). The experimental results are as follows: Figure 4 The results showed that the removal rate of Cr(VI) gradually increased with the increase of stirring speed. At 100 rpm, the removal rate was 58.6%; at 200 rpm, it rose to 73.2%; and at 300 rpm, it reached 85.1%. However, further increases in stirring speed to 400 rpm and 500 rpm resulted in removal rates of 86.5% and 86.8%, respectively, indicating that the improvement in removal efficiency was no longer significant beyond 300 rpm. This may be because excessively high stirring speeds lead to the agglomeration of zero-valent iron particles, reducing their effective specific surface area and thus limiting mass transfer. According to the experimental data, 300 rpm is the optimal stirring speed, under which the mass transfer efficiency is highest, ensuring sufficient contact between ZVI and Cr(VI) and achieving the best removal effect.

[0071] The above are merely embodiments of the present invention, described in a relatively specific and detailed manner, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for treating and regenerating iron-containing waste hydrochloric acid, characterized in that, include: S1: Iron-containing waste hydrochloric acid is evaporated in a multi-effect evaporator. The volatilized HCl gas is absorbed by a water absorption tower to form regenerated hydrochloric acid. The tail gas at the top of the water absorption tower is treated by an alkaline absorption tower. The volatilized HCl gas is exchanged with 20-30℃ cooling water in the first heat exchanger before being sent to the water absorption tower. The evaporation temperature is 80-100℃. After heat exchange in the first heat exchanger, the temperature of the HCl gas is 40-60℃. The regenerated hydrochloric acid obtained after absorption in the water absorption tower has a concentration of 10-20wt% and is sent to the regenerated hydrochloric acid storage tank. The alkaline absorption tower uses a 5-10wt% NaOH solution with a spray density of 10-20 m³ / (m²·h). S2: The liquid material after being processed by the multi-effect evaporator is sent to the second heat exchanger. The cooling water flowing out of the first heat exchanger is sent to the second heat exchanger. After heat exchange, the liquid material is sent to the reactor. After heat exchange in the second heat exchanger, the temperature of the liquid material is 60-80℃. Modified bentonite-loaded nano-zero-valent iron is added to the reactor for reduction reaction. Then, alkali solution is added to adjust the pH. Next, regenerated composite flocculant is added for precipitation reaction. Solid-liquid separation yields the first filter cake and filtrate. S3: Add the regenerated hydrochloric acid from step S1 to the filtrate from step S2 to adjust the pH, then add polyferric chloride, nano-bentonite and oxidant to react, and the resulting product is subjected to solid-liquid separation to obtain regenerated composite flocculant and second filter cake.

2. The method for treating and regenerating iron-containing waste hydrochloric acid as described in claim 1, characterized in that: In S1, the iron-containing waste hydrochloric acid is sent to the third heat exchanger for heat exchange and then to the multi-effect evaporator. The cooling water flowing out of the second heat exchanger is sent to the third heat exchanger to exchange heat with the iron-containing waste hydrochloric acid.

3. The method for treating and regenerating iron-containing waste hydrochloric acid as described in claim 1, characterized in that, In S2, the method for preparing the modified bentonite-supported nano-zero-valent iron is as follows: (1) First grind the bentonite through a 200-mesh sieve, then wash it with deionized water and dry it; (2) Mix bentonite and CTAB at a weight ratio of 20:1, stir and react at 60-80℃ for 2-4 hours. After the reaction is completed, wash with deionized water until there is no CTAB residue, dry, and pulverize to a particle size of 1-100nm to obtain nano-sized modified bentonite. (3) Disperse nano-sized modified bentonite in deionized water to form a modified bentonite suspension; add nano-zero valent iron particles with a purity ≥99% and a particle size of 100-200 mesh to the modified bentonite suspension, with a mass ratio of nano-zero valent iron particles to modified bentonite of 1:10, stir and react for 1-2 hours, separate the solid and liquid, and dry the solid product under nitrogen protection to obtain nano-zero valent iron supported on modified bentonite.

4. The method for treating and regenerating iron-containing waste hydrochloric acid as described in claim 1, characterized in that: In S2, the dosage of modified bentonite-supported nano-zero-valent iron is 5-30 g / L, the pH is adjusted to 7-9 by adding alkaline solution, and the dosage of regenerated composite flocculant is 10-50 mg / L. In S3, regenerated hydrochloric acid is added to adjust the pH to 4-5, the dosage of polyferric chloride is 10-50 mg / L, the particle size of nano-bentonite is 1-100nm and the dosage is 1-5 g / L, and the oxidant is 30wt% hydrogen peroxide with a dosage of 0.1-0.5 g / L.

5. A treatment and regeneration device for iron-containing waste hydrochloric acid, characterized in that, include: The hydrochloric acid evaporation and regeneration unit includes a multi-effect evaporator, a water absorption tower, and an alkali absorption tower connected in sequence by pipelines. The upper part of the alkali absorption tower is connected to an alkali storage tank by a pipeline, and the lower part is connected to a tail liquid tank by a pipeline. The lower part of the water absorption tower is connected to a regenerated hydrochloric acid storage tank by a pipeline. The waste liquid removal unit includes a reaction vessel, a first pH adjustment tank, a flocculation reaction tank, and a first solid-liquid separation device connected in sequence by pipes. The upper part of the reaction vessel is connected by a pipe to a reducing agent storage tank for storing nano-zero-valent iron loaded with modified bentonite. The lower part of the multi-effect evaporator is connected to the reaction vessel by a pipe. The first pH adjustment tank is connected to an alkaline solution storage tank by a pipe. The flocculation reaction tank is connected to a regenerated composite flocculant storage tank by a pipe. The solid material outlet of the first solid-liquid separation device discharges the first filter cake. The regenerated composite flocculant preparation unit includes a second pH adjustment tank, a mixing reaction tank, and a second solid-liquid separation device connected in sequence by pipelines. The upper part of the second pH adjustment tank is connected to the regenerated hydrochloric acid storage tank and the outlet of the first solid-liquid separation device, respectively. The lower part of the second pH adjustment tank is connected to the mixing reaction tank. The upper part of the mixing reaction tank is also connected to a polyferric chloride feeding device, a nano-bentonite feeding device, and an oxidant feeding device, respectively. The outlet of the second solid-liquid separation device is connected to the regenerated composite flocculant storage tank, and the solid material outlet of the second solid-liquid separation device discharges the second filter cake.

6. The iron-containing waste hydrochloric acid treatment and regeneration equipment as described in claim 5, characterized in that: A first heat exchanger is provided between the multi-effect evaporator and the water absorption tower, a second heat exchanger is provided between the multi-effect evaporator and the reaction vessel, and a third heat exchanger is provided on the pipeline into which the multi-effect evaporator inputs iron-containing waste hydrochloric acid. External circulating cooling water flows through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence via the water supply pipeline and then flows back into the return water pipe.

7. The iron-containing waste hydrochloric acid treatment and regeneration equipment as described in claim 6, characterized in that: A branch pipe is installed on the pipeline between the third heat exchanger and the return water pipe, and this branch pipe is connected to the water absorption tower.

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