Iron-containing waste hydrochloric acid treatment and regeneration equipment and method

Abstract

The invention provides iron-containing waste hydrochloric acid treatment and regeneration equipment and method, and relates to the technical field of waste acid resourceful treatment. The iron-containing waste hydrochloric acid treatment regeneration equipment comprises a hydrochloric acid evaporation regeneration unit, a waste liquid impurity removal unit and a regenerated composite flocculant preparation unit. The method provided by the invention realizes recovery of waste hydrochloric acid, reduction removal of hexavalent chromium and preparation of the regenerated composite flocculant, and has multiple advantages of cyclic utilization of resources and efficient removal of pollutants.

Description

Technical Field

[0001] The present invention relates to the technical field of waste acid resource treatment, and particularly to an iron-containing waste hydrochloric acid treatment and regeneration device and method. Background Art

[0002] In industries such as electroplating, leather, and chemical engineering, iron-containing waste hydrochloric acid is a common waste liquid, mainly originating from processes such as pickling, etching, and neutralization. It is characterized by high acidity, high iron content, and heavy metal pollution. This waste hydrochloric acid usually contains iron ions (Fe 2+ or Fe 3+ ) and heavy metal chromium ions, etc. Hexavalent chromium has extremely strong toxicity and carcinogenicity, and its high mobility makes the environmental pollution problem more serious. Therefore, the removal of hexavalent chromium is an important research direction in the field of water treatment. Traditional chromium removal methods include chemical reduction method, adsorption method, and biodegradation method, but these methods have problems such as slow reaction rate, complex operation, and high cost in practical applications.

[0003] The methods for the recovery and utilization of iron-containing waste hydrochloric acid mainly include neutralization method, direct roasting method, extraction method, evaporation concentration method, membrane separation method (diffusion dialysis method, electrodialysis method, air-lift membrane filtration method, etc.). The traditional neutralization method has been eliminated by most enterprises due to high treatment costs and difficult disposal of precipitation sludge. The high-temperature roasting method, although it has high economic value in recovering hydrochloric acid and iron oxide powder, is only industrially applied by large steel enterprises because of large upfront investment, strict equipment and process requirements. The residual iron content in the effluent after crystallization treatment by the evaporation crystallization method cannot meet the standards. The ion exchange method and membrane treatment method are restricted by the high iron content, and are prone to resin and membrane pollution. The evaporation distillation method has a small product market capacity and it is difficult to guarantee the product quality.

[0004] In summary, in view of the severe situation of the current treatment of iron-containing waste hydrochloric acid, it is imperative to develop a new type of iron-containing waste hydrochloric acid treatment and regeneration device and method that can achieve waste hydrochloric acid recovery, efficient removal of pollutants, and resource recycling. Summary of the Invention

[0005] The purpose of the present invention is to provide an iron-containing waste hydrochloric acid treatment and regeneration device and method to solve the problems raised in the above background art.

[0006] In the first aspect, the present invention provides an iron-containing waste hydrochloric acid treatment and regeneration method, including:

[0007] S1: The iron-containing waste hydrochloric acid is evaporated and treated by a multi-effect evaporator, and 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 alkali solution absorption tower;

[0008] S2: The liquid material treated by the multi-effect evaporator is fed into the reaction kettle. Nano zero-valent iron supported on modified bentonite is added to the reaction kettle for a reduction reaction. Then, an alkali solution is added to adjust the pH. Next, a regenerated composite flocculant is added for a precipitation reaction, and solid-liquid separation is performed to obtain a first filter cake and a filtrate.

[0009] S3: In the filtrate of step S2, the regenerated hydrochloric acid of step S1 is added to adjust the pH. Then, polyferric chloride, nano-bentonite, and an oxidant are added thereto for a reaction. The resulting product is subjected to solid-liquid separation to obtain a regenerated composite flocculant and a second filter cake.

[0010] In a preferred embodiment of the present invention, in S1, the volatilized HCl gas is heat-exchanged with cooling water at 20 - 30 °C through a first heat exchanger and then fed into a water absorption tower. The evaporation treatment temperature is 80 - 100 °C. After heat-exchange through the first heat exchanger, the temperature of the HCl gas is 40 - 60 °C. The concentration of the regenerated hydrochloric acid obtained after absorption by the water absorption tower is 10 - 20 wt%, and it is fed into a regenerated hydrochloric acid storage tank. The alkali solution absorption tower uses a 5 - 10 wt% NaOH solution, and the spraying density is 10 - 20 m 3 / (m 2 ·h).

[0011] In a preferred embodiment of the present invention, in S2, the liquid material treated by the multi-effect evaporator is fed into a second heat exchanger, and the cooling water flowing out of the first heat exchanger is fed into the second heat exchanger. The liquid material is heat-exchanged and then fed into the reaction kettle. After heat-exchange through the second heat exchanger, the temperature of the liquid material is 60 - 80 °C.

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

[0013] In a preferred embodiment of the present invention, in S2, the preparation method of the nano zero-valent iron supported on modified bentonite 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 the bentonite and CTAB in a weight ratio of 20:1, stir and react at 60 - 80 °C for 2 - 4 h. After the reaction ends, wash it with deionized water until there is no CTAB residue, dry it, and crush it to a particle size of 1 - 100 nm to obtain nano-scale modified bentonite.

[0016] (3)Disperse the nano-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 into the modified bentonite suspension. The mass ratio of the nano-zero-valent iron particles to the modified bentonite is 1:10. Stir and react for 1 - 2 h, then perform solid-liquid separation, and dry the solid product under nitrogen protection to obtain nano-zero-valent iron supported by modified bentonite.

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

[0018] In a preferred embodiment of the present invention, in S2, add an alkali solution 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 S3, add regenerated hydrochloric acid 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, the dosage is 1 - 5 g / L, and the oxidant is 30 wt% hydrogen peroxide with a dosage of 0.1 - 0.5 g / L.

[0020] In a second aspect, the present invention provides a treatment and regeneration device for iron-containing waste hydrochloric acid, including:

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

[0022] A waste liquid impurity removal unit, which includes a reaction kettle, a first pH adjustment tank, a flocculation reaction tank, and a first solid-liquid separation device connected in sequence through pipelines. The upper part of the reaction kettle is connected to a reductant storage tank for storing nano-zero-valent iron supported by modified bentonite through a pipeline. The lower part of the multi-effect evaporator is connected to the reaction kettle through a pipeline. The first pH adjustment tank is connected to the alkali solution storage tank through a pipeline. The flocculation reaction tank is connected to a regenerated composite flocculant storage tank through a pipeline. The solid material outlet of the first solid-liquid separation device discharges the first filter cake;

[0023] A regenerated composite flocculant preparation unit, which includes a second pH adjustment tank, a mixing reaction tank, and a second solid-liquid separation device connected in sequence through pipelines. The upper part of the second pH adjustment tank is respectively connected to the regenerated hydrochloric acid storage tank and the liquid outlet of the first solid-liquid separation device. 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 respectively connected to a polyferric chloride feeding device, a nano-bentonite feeding device, and an oxidant feeding device. The liquid outlet of the second solid-liquid separation device is connected to a 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 kettle, and a third heat exchanger is provided on the pipeline for inputting iron-containing waste hydrochloric acid into the multi-effect evaporator. The external circulating cooling water flows through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence through the water supply pipeline and then flows back into the return pipe.

[0025] In a preferred embodiment of the present invention, a branch pipeline is provided on the pipeline between the third heat exchanger and the return pipe, and this branch pipeline 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] The present invention realizes the recovery of waste hydrochloric acid, the reduction and removal of hexavalent chromium, and the preparation of a regenerated composite flocculant, and has multiple advantages of resource recycling and efficient removal of pollutants; by setting the multi-effect evaporator, the first heat exchanger, the second heat exchanger, and the third heat exchanger, the heat energy utilization efficiency is improved, the energy consumption in the evaporation process is reduced, and the HCl recovery rate is high and the operation is stable; by recycling hydrochloric acid and preparing a regenerated composite flocculant and recycling it, the raw material cost is reduced. The regenerated composite flocculant has flocculation, adsorption, and oxidation functions and is a multifunctional water treatment agent suitable for wastewater treatment; the first filter cake and the second filter cake produced are rich in chromium and iron, and are easy to be treated by harmless or resource utilization after centralized collection, reducing waste discharge. Description of the Drawings

[0028] Figure 1 It is a schematic structural diagram of a device for treating and regenerating iron-containing waste hydrochloric acid in Example 1;

[0029] Figure 2 It is a line graph showing the effect of the dosage of nano zero-valent iron supported on modified bentonite on the Cr(VI) removal rate in Experimental Example 1;

[0030] Figure 3 It is a line graph showing the effect of the initial pH value of different waste acids on the Cr(VI) removal rate in Experimental Example 2;

[0031] Figure 4 It is a line graph showing the effect of different stirring rates on the chromium removal efficiency in Experimental Example 5;

[0032] Reference numerals: 1 - multi - effect evaporator, 2 - water absorption tower, 3 - reaction kettle, 4 - first heat exchanger, 5 - second heat exchanger, 6 - third heat exchanger, 7 - lye absorption tower, 8 - lye 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 - mixing reaction tank, 21 - second solid - liquid separation device. Detailed implementation manners

[0033] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments.

[0034] Embodiment 1

[0035] Please refer to the attached Figure 1 As shown, a treatment and regeneration device for iron - containing waste hydrochloric acid in this embodiment includes:

[0036] A hydrochloric acid evaporation and regeneration unit, which includes a multi - effect evaporator 1, a water absorption tower 2, and a lye absorption tower 7 connected in sequence through pipelines. The upper part of the lye absorption tower 7 is connected to the lye storage tank 8 through a pipeline, and its lower part is connected to the tail liquid tank 10 through a pipeline. The lower part of the water absorption tower 2 is connected to the regenerated hydrochloric acid storage tank 9 through a pipeline;

[0037] A waste liquid impurity removal unit, which includes a reaction kettle 3, a first pH adjustment tank 12, a flocculation reaction tank 13, and a first solid - liquid separation device 14 connected in sequence through pipelines. The upper part of the reaction kettle 3 is connected to a reducing agent storage tank 11 for storing nano - zero - valent iron loaded on modified bentonite through a pipeline. The lower part of the multi - effect evaporator 1 is connected to the reaction kettle 3 through a pipeline. The first pH adjustment tank 12 is connected to the lye storage tank 8 through a pipeline. The flocculation reaction tank 13 is connected to the regenerated composite flocculant storage tank 15 through a pipeline. The solid material outlet of the first solid - liquid separation device 14 discharges the first filter cake;

[0038] A regenerated composite flocculant preparation unit, which includes a second pH adjustment tank 16, a mixing reaction tank 20, and a second solid - liquid separation device 21 connected in sequence through pipelines. The upper part of the second pH adjustment tank 16 is respectively connected to the regenerated hydrochloric acid storage tank 9 and the liquid outlet of the first solid - liquid separation device 14. 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 respectively connected to a polyferric chloride feeding device 17, a nano - bentonite feeding device 18, and an oxidant feeding device 19. The liquid outlet of the second solid - liquid separation device 21 is connected to the regenerated composite flocculant storage tank 15. The solid material outlet of the second solid - liquid separation device 21 discharges the second filter cake.

[0039] In this embodiment, the iron-containing waste hydrochloric acid enters the multi-effect evaporator 1, and HCl gas is heated and evaporated. The HCl gas enters the water absorption tower 2 to generate regenerated hydrochloric acid, while the unabsorbed HCl gas enters the alkali solution absorption tower 7 to generate NaCl solution. The concentrated waste liquid discharged from the multi-effect evaporator 1 enters the reaction kettle 3 and reacts with the nano zero-valent iron supported by modified bentonite. Cr 6+ is reduced to Cr 3+ , then the waste liquid enters the first pH adjustment tank 12, and alkali is added to adjust the pH to generate Cr(OH)3 precipitate. Then the waste liquid enters the flocculation reaction tank 13, and a 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 the precipitate. The supernatant discharged from the first solid-liquid separation device 14 enters the second pH adjustment tank 16, and the pH is adjusted with regenerated hydrochloric acid. The waste liquid enters the mixing reaction tank 20, and 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 and is used for the waste liquid impurity removal unit.

[0040] 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 kettle 3, and a third heat exchanger 6 is provided on the pipeline for inputting the iron-containing waste hydrochloric acid into the multi-effect evaporator 1. The external circulating cooling water flows through the first heat exchanger 4, the second heat exchanger 5, and the third heat exchanger 6 in sequence through the water supply pipeline and then flows back into the return pipe; a branch pipeline is provided on the pipeline between the third heat exchanger 6 and the return pipe, and this branch pipeline is connected to the water absorption tower 2. A heat exchange system is formed through the first heat exchanger 4, the second heat exchanger 5, and the third heat exchanger 6 to improve the thermal energy utilization efficiency of the hydrochloric acid evaporation and regeneration unit and reduce the energy consumption during the evaporation process.

[0041] Embodiment 2

[0042] Based on Embodiment 1, this embodiment provides a method for treating and regenerating iron-containing waste hydrochloric acid. The specific steps include:

[0043] S1: The iron-containing waste hydrochloric acid is evaporated and treated by a multi-effect evaporator, and the volatilized HCl gas is absorbed by the water absorption tower to form regenerated hydrochloric acid. The tail gas at the top of the water absorption tower is treated by the alkali solution absorption tower;

[0044] S2: The liquid material treated by the multi-effect evaporator is sent to the reaction kettle, and nano zero-valent iron supported by modified bentonite is added to the reaction kettle for a reduction reaction. Then alkali solution is added to adjust the pH, and then a regenerated composite flocculant is added for a precipitation reaction. Solid-liquid separation is carried out to obtain the first filter cake and the filtrate;

[0045] S3: In the filtrate of step S2, the regenerated hydrochloric acid of step S1 is added to adjust the pH, and then polyferric chloride, nano bentonite and an oxidant are added to react. The obtained product is subjected to solid-liquid separation to obtain the regenerated composite flocculant and the second filter cake.

[0046] In this embodiment, the volatilized HCl gas is heat-exchanged with cooling water at 20 - 30°C in the first heat exchanger and then sent to the water absorption tower. 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 concentration of the regenerated hydrochloric acid obtained after absorption in the water absorption tower is 10 - 20 wt%, and it is sent to the regenerated hydrochloric acid storage tank. The alkaline solution absorption tower uses a 5 - 10 wt% NaOH solution, and the spraying density is 10 - 20 m 3 / (m 2 ·h). While the first heat exchanger reduces the temperature of the HCl gas, it reduces the heat load of the water absorption tower. The cooled HCl gas enters the water absorption tower and contacts the water in the tower countercurrently. The water absorption tower and the alkaline solution absorption tower use a packed tower or a spraying tower to improve the gas-liquid contact efficiency.

[0047] In this embodiment, the liquid material treated 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 reaction kettle. After heat-exchange in the second heat exchanger, the temperature of the liquid material is 60 - 80°C. The liquid material treated by the multi-effect evaporator is cooled in the second heat exchanger, reducing the heat load of the reaction kettle and, at the same time, making the liquid material at the appropriate reaction temperature of the nano zero-valent iron loaded on the modified bentonite, avoiding the influence of too high temperature on the reaction activity of the nano zero-valent iron loaded on the modified bentonite and restricting the removal rate.

[0048] In this embodiment, the iron-containing waste hydrochloric acid is sent to the third heat exchanger for heat-exchange and then sent to the multi-effect evaporator. The cooling water flowing out of the second heat exchanger is sent to the third heat exchanger for heat-exchange with the iron-containing waste hydrochloric acid. The iron-containing waste hydrochloric acid is preheated by the third heat exchanger to reduce the evaporation energy consumption.

[0049] Specifically, in S2, the dosage of the nano zero-valent iron loaded on the modified bentonite is 5 - 30 g / L, the pH is adjusted to 7 - 9 by adding an alkaline solution, and the dosage of the regenerated composite flocculant is 10 - 50 mg / L; in S3, the pH is adjusted to 4 - 5 by adding the regenerated hydrochloric acid, the dosage of polyferric chloride is 10 - 50 mg / L, the particle size of the nano bentonite is 1 - 100 nm, the dosage is 1 - 5 g / L, and the oxidant uses 30 wt% hydrogen peroxide, and the dosage is 0.1 - 0.5 g / L.

[0050] In this embodiment, both the first solid-liquid separation device and the second solid-liquid separation device use a plate and frame filter press, the pressure is controlled at 0.2 - 0.5 MPa, the reaction kettle is equipped with a stirring mechanism, the stirring speed is controlled at 100 - 500 rpm, the stirring speed is controlled at 50 - 100 rpm during the reaction in the flocculation reaction tank, the flocculation time is 10 - 30 min, and the stirring speed is controlled at 100 - 200 rpm during the reaction in the mixing reaction tank.

[0051] In this embodiment, the composition of the first filter cake includes Cr(OH)3, Fe(OH)3, modified bentonite, and other impurities, and the composition of the second filter cake includes Fe(OH)3, nano-bentonite, Cr(OH)3, and other impurities.

[0052] Since the solid impurities in the first filter cake and the second filter cake have certain similarities in composition and properties, they can be processed for resource utilization together. Iron resources are used to prepare Fe2O3 or Fe3O4 through high-temperature calcination or reduction calcination. Fe2O3 is used to prepare pigments, magnetic materials, or catalysts, etc., and Fe3O4 is used to prepare magnetic materials or battery electrodes. Chromium resources are converted into Cr2O3 through oxidation and used to prepare pigments, catalysts, or refractory materials. Bentonite resources are recovered through pickling or alkali washing, and bentonite can be reused for loading nZVI or as an adsorbent.

[0053] In this embodiment, the preparation method of the nano-zero-valent iron loaded on the modified bentonite is as follows:

[0054] (1) First, grind the bentonite through a 200-mesh sieve, then wash it with deionized water and dry it.

[0055] (2) Mix the bentonite and CTAB in a weight ratio of 20:1, stir and react at 60 - 80 °C for 2 - 4 h. After the reaction, wash it with deionized water until there is no residual CTAB, dry it, and crush it to a particle size of 1 - 100 nm to obtain nano-scale modified bentonite.

[0056] (3) Disperse the nano-scale 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. The mass ratio of the nano-zero-valent iron particles to the modified bentonite is 1:10. Stir and react for 1 - 2 h, perform solid-liquid separation, and dry the solid product under nitrogen protection to obtain the nano-zero-valent iron loaded on the modified bentonite.

[0057] Next, experiments are conducted to study the effects of the dosage of the nano-zero-valent iron loaded on the modified bentonite, the initial pH of the waste acid, the reaction time, the temperature, and the stirring rate on the chromium removal effect in this embodiment.

[0058] In the experiment, the Cr(VI) simulated waste acid solution is prepared from K2Cr2O7, and the initial Cr(VI) concentration is strictly controlled at 100 mg / L. The pH value is adjusted by 0.1 mol / L HCl or NaOH, and the range is set from 1 to 5.

[0059] Experimental Example 1: Effect of the Dosage of the Nano-Zero-Valent Iron Loaded on the Modified Bentonite on the Chromium Removal Effect

[0060] The removal effect of Cr(VI) in waste acid was evaluated using nano zero-valent iron (ZVI) loaded on modified bentonite with different dosages. The results are as Figure 2 shown. The results showed that with the increase in the dosage of ZVI, the removal rate of Cr(VI) increased significantly: the removal rate was 45% at 5 g / L, rose to 67.5% at 10 g / L, was 82% at 15 g / L, and reached 90% at 20 g / L, and stabilized at 91% at 25 g / L. This saturation phenomenon of the removal rate indicates that as the surface active sites of ZVI become saturated, the reaction rate is limited, and the additional addition of ZVI no longer significantly improves the removal effect. In addition, the particle aggregation caused by too high a dosage further reduces the effective specific surface area of ZVI and affects the mass transfer efficiency. The experimental results conform to the Langmuir adsorption model, and 20 g / L was determined as the optimal dosage, achieving efficient removal of Cr(VI) while avoiding excessive use of materials.

[0061] Experimental Example 2 Effect of the initial pH of waste acid on the chromium removal effect

[0062] The removal effect of Cr(VI) in waste acid was evaluated using waste acid with different pH values in the pH range of 3 - 11. The results are as Figure 3 shown. The results showed that under acidic conditions (pH 3 to 5), the removal rate of Cr(VI) was the highest, especially at pH 5, where the removal rate reached 88.5%. At this time, the reaction between ZVI and Cr2O7 2- was the most sufficient. The acidic environment promoted the corrosion reaction of ZVI and accelerated the reduction of Cr(VI), increasing the reaction rate and electron transfer efficiency. When the pH value increased to neutral and alkaline (pH 7 to 11), the removal efficiency decreased significantly. At pH 7, the removal rate was 70%, indicating that the removal ability of ZVI began to be limited by the passivation layer. As the pH further increased to 9 and 11, the removal rates decreased to 58% and 43% respectively. Under alkaline conditions, the oxide layer formed on the surface of ZVI significantly reduced the reduction reaction efficiency of Cr(VI), resulting in CrO4 2- being difficult to react effectively with ZVI at higher pH values. During the experiment, a Mettler Toledo pH meter was used to accurately control the initial pH of the solution, 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.

[0063] Experimental Example 3 Effect of reaction time on the chromium removal efficiency

[0064] By setting different reaction times (15 min, 30 min, 60 min, 120 min, 180 min, 240 min), the effect of reaction time on the removal efficiency of Cr(VI) was studied. The results are as Figure 4As shown. The results indicate that: in the initial stage (0 to 60 min), the removal rate of Cr(VI) increased rapidly, rising from 52% at 15 min to 82% at 60 min, mainly because there were more active sites on the surface of ZVI at the beginning of the reaction, and Cr(VI) could be rapidly reduced. When the reaction time was extended to 120 min, the removal rate reached 90%, but the subsequent removal rate decreased significantly, and the removal rate at 240 min only slightly increased to 93%, indicating that the reaction was approaching equilibrium. By fitting the experimental data, the reaction process conforms to the pseudo-first-order kinetic model, and its kinetic equation is:

[0065]

[0066] 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 the data fitting, the value of the reaction rate constant kobs within the initial 60 minutes was relatively large, approximately 0.032 min-1, indicating that the reduction of Cr(VI) at this stage was mainly controlled by diffusion mass transfer. As the reaction time extended, the surface passivation phenomenon increased, resulting in a reduction in the effective reaction sites and mass transfer limitation, and the reaction rate gradually decreased. The Cr(VI) concentration was measured by the diphenylcarbazide method using an Agilent Cary 60 UV-Vis spectrophotometer at a wavelength of 540 nm to ensure the measurement accuracy and data repeatability at each time point.

[0067] Experimental Example 4 Effect of Temperature on Chromium Removal Efficiency

[0068] Five different temperature conditions of 10°C, 20°C, 30°C, 40°C, and 50°C were set to study the effect of reaction time on the Cr(VI) removal efficiency. The results show that: with the increase in temperature, the removal rate of Cr(VI) increased significantly. At 10°C, the removal rate was 65.2%, while at 30°C it reached 87.4%. This increase was attributed to the fact that the increase in temperature accelerated the reaction rate and the surface activity of zero-valent iron (ZVI). When the temperature rose to 50°C, the removal rate leveled off at 91.5%, indicating that the reaction was gradually approaching saturation. The reaction rate constant k was fitted by the Arrhenius equation:

[0069]

[0070] Among them, 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 fitting data, the activation energy Ea for the reduction of Cr(VI) by ZVI is 28.6 kJ / mol, indicating that the reaction is relatively sensitive to temperature and the rate is controlled by diffusion. The study also found that at high temperatures, the formation rate of iron corrosion products and passivation layers increases, resulting in a reduction in the number of effective reaction sites, thereby limiting the further improvement of the removal rate. In the experiment, a constant temperature water bath was used to control the temperature, and a UV-Vis spectrophotometer was used to measure the residual concentration of Cr(VI) at different temperatures.

[0071] Experimental Example 5 Effect of Stirring Rate on Chromium Removal Efficiency

[0072] In this experiment, five different stirring rates of 100 rpm, 200 rpm, 300 rpm, 400 rpm, and 500 rpm were set, while other experimental conditions remained unchanged (ZVI dosage of 20 g / L, initial Cr(VI) concentration of 100 mg / L, pH 5, temperature of 30 °C). The experimental results showed that as the stirring rate increased, the removal rate of Cr(VI) gradually increased. At 100 rpm, the removal rate was 58.6%; at 200 rpm, the removal rate increased to 73.2%; when the stirring rate increased to 300 rpm, the removal rate reached 85.1%. However, when the stirring rate was further increased to 400 rpm and 500 rpm, the removal rates were 86.5% and 86.8% respectively, indicating that the improvement in removal efficiency was no longer obvious after the stirring rate exceeded 300 rpm. This may be due to the aggregation of zero-valent iron particles at too high a stirring rate, reducing their effective specific surface area and thus limiting the mass transfer effect. According to the experimental data, 300 rpm is the optimal stirring rate, under which the mass transfer efficiency is the highest, ensuring sufficient contact between ZVI and Cr(VI) to achieve the optimal removal effect.

[0073] The above is only the implementation mode of the present invention, and its description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to 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: The iron-containing waste hydrochloric acid is evaporated by a multi-effect evaporator, and 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 alkali liquid absorption tower; S2: the liquid material treated by the multiple-effect evaporator is sent to the reactor, and the nano zero-valent iron loaded with modified bentonite is added to the reactor for reduction reaction, and then alkali solution is added to adjust the pH, and then the regenerated composite flocculant is added for precipitation reaction, and the first filter cake and filtrate are obtained by solid-liquid separation; S3: adding the regenerated hydrochloric acid of step S1 to the filtrate of step S2 to adjust the pH, then adding polyferric chloride, nano-bentonite and an oxidant thereto to react, and performing solid-liquid separation on the obtained product to obtain a regenerated composite flocculant and a second filter cake.

2. A method for treating and regenerating iron-containing waste hydrochloric acid according to claim 1, characterized in that: In S1, the volatilized HCl gas is heat exchanged with 20-30°C cooling water in the first heat exchanger and then sent to the water absorption tower. The evaporation treatment temperature is 80-100°C. The temperature of the HCl gas after heat exchange in the first heat exchanger is 40-60°C. The regenerated hydrochloric acid concentration obtained after absorption in the water absorption tower is 10-20wt%, and is sent to the regenerated hydrochloric acid storage tank; the alkali liquid absorption tower uses 5-10wt% NaOH solution, and the spray density is 10-20m 3 / (m 2 h).

3. A method for treating and regenerating iron-containing waste hydrochloric acid according to claim 1, characterized in that: In S2, the liquid material treated 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. The liquid material is sent to the reactor after heat exchange. The temperature of the liquid material after heat exchange in the second heat exchanger is 60-80°C.

4. A method for treating and regenerating iron-containing waste hydrochloric acid according to claim 1, characterized in that: In S1, the iron-containing waste hydrochloric acid is sent to the third heat exchanger and then to the multi-effect evaporator, and 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.

5. The method for treating and regenerating iron-containing waste hydrochloric acid according to claim 1, characterized in that: In S2, the preparation method of the modified bentonite-supported nano zero-valent iron is: (1) Grind the bentonite through a 200-mesh sieve, wash with deionized water, and dry; (2) Mixing bentonite and CTAB in a weight ratio of 20:1, stirring and reacting at 60-80° C. for 2-4 hours, washing with deionized water until no CTAB remains after the reaction, drying, and crushing to a particle size of 1-100 nm to obtain nano-modified bentonite; (3) Dispersing nano-scale modified bentonite in deionized water to form a modified bentonite suspension; adding nano-zero-valent iron particles with a purity of ≥99% and a particle size of 100-200 mesh to the modified bentonite suspension, wherein the mass ratio of nano-zero-valent iron particles to modified bentonite is 1:10, stirring the reaction for 1-2 hours, separating the solid and the liquid, and drying the solid product under nitrogen protection to obtain nano-zero-valent iron loaded on modified bentonite.

6. The method for treating and regenerating iron-containing waste hydrochloric acid according to claim 1, characterized in that: In S2, the dosage of nano zero-valent iron loaded with modified bentonite is 5-30 g / L, alkali solution is added to adjust the pH to 7-9, 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 1-100 nm, the dosage is 1-5 g / L, and the oxidant is 30wt% hydrogen peroxide, the dosage is 0.1-0.5 g / L.

7. A device for treating and regenerating iron-containing waste hydrochloric acid, characterized in that: include: The hydrochloric acid evaporation regeneration unit comprises a multi-effect evaporator, a water absorption tower, and an alkali solution absorption tower which are sequentially connected through pipelines, wherein the upper part of the alkali solution absorption tower is connected to the alkali solution storage tank through a pipeline, and the lower part of the alkali solution absorption tower is connected to the tail liquid tank through a pipeline, and the lower part of the water absorption tower is connected to the regeneration hydrochloric acid storage tank through a pipeline; A waste liquid impurity removal unit, comprising a reactor, a first pH adjustment tank, a flocculation reaction tank, and a first solid-liquid separation device connected in sequence through pipelines, wherein the upper portion of the reactor is connected to a reducing agent storage tank for storing nano zero-valent iron loaded with modified bentonite through a pipeline, the lower portion of the multiple-effect evaporator is connected to the reactor through a pipeline, the first pH adjustment tank is connected to an alkali solution storage tank through a pipeline, the flocculation reaction tank is connected to a regenerated composite flocculant storage tank through a pipeline, and the solid material outlet of the first solid-liquid separation device discharges a first filter cake; The regenerated composite flocculant preparation unit comprises a second pH adjusting tank, a mixing reaction tank, and a second solid-liquid separation device which are sequentially connected by pipelines, wherein the upper portion of the second pH adjusting tank is respectively connected to a regenerated hydrochloric acid storage tank and a liquid outlet of the first solid-liquid separation device, the lower portion of the second pH adjusting tank is connected to the mixing reaction tank, the upper portion of the mixing reaction tank is also respectively connected to a polyferric chloride feeding device, a nano-bentonite feeding device, and an oxidant feeding device, the liquid 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 a second filter cake.

8. The iron-containing waste hydrochloric acid treatment and regeneration equipment according to claim 7, characterized in that: A first heat exchanger is provided between the multiple-effect evaporator and the water absorption tower, a second heat exchanger is provided between the multiple-effect evaporator and the reactor, a third heat exchanger is provided on the pipeline for inputting iron-containing waste hydrochloric acid into the multiple-effect evaporator, and external circulating cooling water flows through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence through the water supply pipeline and then flows back into the return water pipe.

9. The iron-containing waste hydrochloric acid treatment and regeneration equipment according to claim 8, characterized in that: A branch pipeline is arranged on the pipeline between the third heat exchanger and the return water pipe, and the branch pipeline is connected to the water absorption tower.

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