A process for preparing iron concentrate and high-purity zinc oxide from hot galvanizing waste acid

Abstract

The present application relates to the technical field of industrial waste resource utilization, and discloses a process for preparing iron fine powder and high-purity zinc oxide from hot galvanizing waste acid, which comprises the following steps: first, adding a crystal face directing agent containing polyethylene glycol and ascorbic acid into the heated waste acid, and then adding a zinc source for replacement; monitoring the oxidation-reduction potential in real time, starting a high-shear dispersion mode when the potential drops to a threshold value, and introducing the slurry into an external circulation loop comprising a magnetic separation device, using a magnetic field to trap the iron powder, and returning the permeable magnetic liquid to the system until the reaction endpoint; the separated iron powder is treated to obtain iron fine powder; the filtrate is subjected to hydrothermal reaction to prepare nano zinc oxide after impurity removal; and the calcium chloride mother liquor is added into concentrated sulfuric acid for high-temperature evaporation crystallization under negative pressure, and the regenerated hydrochloric acid is recovered by condensation, and calcium sulfate whiskers are collected. The present application solves the problems of iron passivation and separation, and realizes the high-value recovery and utilization of all components of the waste acid.

Description

Technical Field

[0001] This invention relates to the field of industrial waste resource utilization technology, specifically a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid. Background Technology

[0002] Hot-dip galvanizing is one of the main methods of steel corrosion protection. In its pretreatment process, hydrochloric acid is used to pickle and remove rust from steel workpieces, generating a large amount of waste acid. This waste acid typically contains high concentrations of ferrous chloride, zinc chloride, and residual free hydrochloric acid. Direct discharge of this waste acid not only causes serious soil and water pollution but also represents a huge waste of iron, zinc, and chlorine resources.

[0003] Currently, the main method for treating waste acid from hot-dip galvanizing is neutralization precipitation. This method adjusts the pH value by adding lime or sodium hydroxide, causing iron and zinc ions to precipitate as hydroxides. Although simple to operate, this method cannot achieve high-value separation of iron and zinc, ultimately producing a large amount of mixed sludge containing heavy metals, which is classified as hazardous waste. Subsequent disposal is costly and prone to causing secondary pollution.

[0004] To achieve resource recovery, the industry has attempted to use the zinc powder displacement method to recover iron from waste acid. The basic principle is that zinc is more reactive than iron, displacing ferrous ions in the solution with metallic iron precipitate. However, this method faces technical bottlenecks in practical industrial applications. Because the displacement reaction occurs at the solid-liquid interface, the generated metallic iron tends to deposit tightly on the surface of the zinc powder particles, forming a dense coating. This coating layer blocks the contact between the unreacted zinc inside and the external waste acid, leading to sluggish or even passivated reaction kinetics, resulting in low zinc powder utilization and incomplete reaction. Furthermore, even if some iron powder detaches, the extremely fine particle size of the displaced iron powder and the insignificant density difference with the residual zinc powder make it difficult to effectively separate them using conventional gravity sedimentation or simple physical filtration. This results in the final iron powder containing a large amount of zinc impurities, and the product purity cannot meet the application requirements of high-end fields such as powder metallurgy.

[0005] In the recovery of zinc oxide products, the conventional process usually involves first precipitating to generate a precursor, and then preparing zinc oxide through high-temperature calcination. The high-temperature calcination process is prone to causing excessive grain growth and sintering necking between particles, resulting in a small specific surface area and poor dispersibility of the final product, making it difficult to use as a highly active raw material in the rubber or catalyst industries.

[0006] In the tail-end processes of waste acid treatment, the regeneration and recycling of hydrochloric acid are typically involved. Conventional atmospheric pressure evaporation processes are limited by the azeotropic properties of hydrogen chloride and water, making it difficult to obtain high concentrations of regenerated hydrochloric acid. More critically, in wet full-cycle processes, the water in the reaction system originates from the raw materials and is generated by the chemical reaction. If water and hydrogen chloride cannot be removed simultaneously and efficiently during the acid regeneration stage, the volume of the circulating mother liquor will continuously expand, disrupting the system's water balance. Ultimately, this forces the production line to maintain operation by discharging the mother liquor, making true zero discharge impossible. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid, solving the problems of reaction passivation and difficulty in separating iron and zinc caused by iron layer encapsulation in traditional displacement methods.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid, comprising the following steps: The waste acid from hot-dip galvanizing is heated, and a composite crystal surface guiding agent solution is added. The mixture is kept at the temperature and stirred to obtain pretreated waste acid. The composite crystal surface guiding agent solution contains polyethylene glycol and ascorbic acid. Pretreated waste acid is introduced into the reaction system, and a zinc source is added under stirring conditions to carry out a displacement reaction. The oxidation-reduction potential of the reaction system is monitored in real time. When the oxidation-reduction potential drops to the first preset threshold, the high shear dispersion mode is activated, and the reaction slurry in the reaction system is introduced into the external circulation loop containing the magnetic separation device. The magnetic field is used to retain the iron powder, and the magnetically clear liquid is returned to the reaction system until the reaction endpoint is reached. The retained iron powder is washed and dried to obtain iron concentrate, and the remaining liquid in the reaction system after reaching the reaction endpoint is filtered to remove impurities, resulting in filtrate. Oxidizing and neutralizing agents were added to the filtrate to remove residual iron, the pH value was adjusted to generate a precursor slurry, a hydrothermal reaction was carried out, and nano zinc oxide and calcium chloride mother liquor were obtained by solid-liquid separation. Concentrated sulfuric acid was added to the calcium chloride mother liquor, and a high-temperature evaporation and crystallization reaction was carried out under negative pressure. The regenerated hydrochloric acid was recovered by condensation, and the calcium sulfate whiskers were collected by centrifugation.

[0009] Preferably, the solute in the composite crystal plane guiding agent solution is composed of polyethylene glycol 600 and L-ascorbic acid, and the mass ratio of polyethylene glycol 600 to L-ascorbic acid is 1:1.2 to 1.2:1; the amount of composite crystal plane guiding agent solution added is 0.05% to 0.1% of the mass of hot-dip galvanizing waste acid.

[0010] Preferably, the composite crystal plane guiding agent solution is prepared by the following method: adding deionized water to a mixing container and heating to 30 to 40 degrees Celsius; first adding polyethylene glycol 600 while stirring until clear and transparent; then adding L-ascorbic acid and stirring until completely dissolved, and cooling to room temperature.

[0011] Preferably, in the displacement reaction step, the reaction temperature is maintained at 70 to 80 degrees Celsius, the zinc source is zinc powder or ball mill zinc slag, and the amount added, based on the effective metallic zinc, is 1.02 to 1.05 times the stoichiometric ratio required for theoretical displacement.

[0012] Preferably, the first preset threshold is -350 mV to -400 mV, and the stirring speed after the high shear dispersion mode is turned on is 250 rpm to 350 rpm.

[0013] Preferably, a hydrocyclone is connected in series in the external circulation loop; the reaction slurry first enters the hydrocyclone for classification, the underflow is returned to the reaction system, and the overflow enters the magnetic separation device, which is a pipeline magnetic separator; the inlet pressure of the hydrocyclone is controlled at 0.15 MPa to 0.25 MPa; the magnetic field strength of the pipeline magnetic separator is set at 3000 Gauss to 5000 Gauss.

[0014] Preferably, the specific process for obtaining nano-zinc oxide and calcium chloride mother liquor is as follows: an oxidant is added to the filtrate, the amount of which is 1.1 to 1.2 times the molar amount of residual ferrous ions, and the pH is adjusted to 5.0 to 5.2 for precipitation to remove residual iron and heavy metal impurities; then lime milk is added to adjust the pH to 8.5 to 9.5 to generate a precursor slurry; the precursor slurry is pumped into a hydrothermal reactor and reacted at 150 to 165 degrees Celsius under autogenous pressure for 3 to 5 hours, followed by solid-liquid separation; the oxidant is hydrogen peroxide.

[0015] Preferably, the molar ratio of concentrated sulfuric acid to calcium chloride in the calcium chloride mother liquor is 1.01:1 to 1.05:1; the negative pressure condition is an absolute system pressure of -0.02 MPa to -0.05 MPa; and the temperature of the high-temperature evaporation crystallization reaction is controlled at 135 degrees Celsius to 145 degrees Celsius.

[0016] Preferably, the high-temperature evaporation crystallization reaction is carried out in a crystallization evaporator lined with polytetrafluoroethylene or glass; the hydrogen chloride and water vapor generated in the reaction are condensed and recovered by a graphite condenser to obtain regenerated hydrochloric acid with a mass concentration of 18% to 20%; the high-temperature evaporation crystallization reaction adopts a continuous mother liquor circulation mode, in which the centrifuged mother liquor after collecting calcium sulfate whiskers from the previous batch is returned to the crystallization evaporator as the bottom liquid for the next batch.

[0017] Preferably, the reaction equipment used in the process of carrying out the displacement reaction until the reaction endpoint is reached is a glass-lined reactor with a heating jacket, and the external circulation loop is lined with polytetrafluoroethylene.

[0018] This invention provides a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid. It has the following beneficial effects: 1. This invention solves the problems of reaction passivation and separation caused by iron powder coating the zinc surface by introducing polyethylene glycol and ascorbic acid into the displacement system and combining high-shear dispersion with magnetic separation technology. Polyethylene glycol induces iron atoms to grow in a loose dendritic structure, ascorbic acid inhibits ferrous oxidation, and the physical stripping effect of the high-shear flow field allows iron powder to detach from the zinc surface in a timely manner, maintaining the activity of the reaction interface. Subsequent online separation using magnetic differences effectively distinguishes iron powder and zinc source with similar densities, improving the purity of iron concentrate and the recovery rate of the displacement reaction.

[0019] 2. This invention employs a stepwise impurity removal and hydrothermal mineralization process to prepare nano-zinc oxide, thereby improving product quality. Iron and heavy metal impurities in the filtrate are pre-removed by the combination of an oxidant and a neutralizing agent. The subsequent hydrothermal reaction environment promotes the dissolution and recrystallization of the precursor in the liquid phase, achieving self-purification of the product through the lattice exclusion effect. This process avoids particle sintering and agglomeration caused by traditional high-temperature calcination methods, resulting in zinc oxide with higher dispersibility and specific surface area.

[0020] 3. This invention utilizes negative pressure high-temperature evaporation crystallization technology to achieve water balance control and high-value utilization of by-products in the acid regeneration system. The negative pressure condition alters the gas-liquid balance of the hydrogen chloride and water system, lowering the azeotropic point and allowing the water generated in the reaction and the water introduced to evaporate simultaneously with the hydrogen chloride. This recovers a high concentration of regenerated hydrochloric acid while removing excess water from the system, preventing volume expansion during mother liquor circulation. Simultaneously, the high-temperature negative pressure environment optimizes the crystallization kinetics of calcium sulfate, promoting the formation of high aspect ratio calcium sulfate whiskers. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a composite crystal plane guiding agent, including the following steps: Add 100 kg of deionized water to a stainless steel mixing vessel equipped with a mechanical stirrer. Turn on the heating jacket to raise the water temperature to 35°C and keep it constant. Turn on the stirrer and set the speed to 150 rpm. Slowly add 15 kg of polyethylene glycol 600 to the water and stir continuously for 15 minutes until the solution changes from turbid to clear and transparent. Then add 15 kg of ascorbic acid to the solution and continue stirring for 10 minutes. After all the solids have dissolved, stop heating and stirring and allow it to cool naturally to room temperature to obtain a composite crystal plane guiding agent solution A with a mass concentration of 23.1%, in which the mass ratio of polyethylene glycol 600 to ascorbic acid is 1:1.

[0023] Preparation Example 2: This preparation example provides a method for preparing a composite crystal plane guiding agent, including the following steps: Add 100 kg of deionized water to a stainless steel mixing vessel equipped with a mechanical stirrer. Turn on the heating jacket to raise the water temperature to 40°C and keep it constant. Turn on the stirrer and set the speed to 200 rpm. Slowly add 18 kg of polyethylene glycol 600 to the water and stir continuously for 20 minutes until completely dissolved. Then add 15 kg of ascorbic acid to the solution and continue stirring for 15 minutes. After the solid is completely dissolved, stop heating and stirring and allow it to cool naturally to room temperature to obtain a composite crystal plane guiding agent solution B with a mass concentration of 24.8%, wherein the mass ratio of polyethylene glycol 600 to ascorbic acid is 1.2:1.

[0024] Preparation Example 3: This preparation example provides a method for preparing a composite crystal plane guiding agent, including the following steps: Add 100 kg of deionized water to a stainless steel mixing vessel equipped with a mechanical stirrer. Turn on the heating jacket to raise the water temperature to 30°C and keep it constant. Turn on the stirrer and set the speed to 120 rpm. Slowly add 12.5 kg of polyethylene glycol 600 to the water and stir continuously for 15 minutes until completely dissolved. Then add 15 kg of ascorbic acid to the solution and continue stirring for 10 minutes. After the solid is completely dissolved, stop heating and stirring and allow it to cool naturally to room temperature to obtain a composite crystal plane guiding agent solution C with a mass concentration of 21.6%, wherein the mass ratio of polyethylene glycol 600 to ascorbic acid is 1:1.2.

[0025] Examples 1-5: Example 1: This embodiment provides a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid, including the following steps: (1) Take 1000 kg of hot-dip galvanized waste acid (including 180 g / L ferrous chloride, 60 g / L zinc chloride, and 8% hydrochloric acid), pump it into a pretreatment vessel with a heating jacket, and heat it to 70°C; add 0.8 kg of the composite crystal plane guiding agent solution A obtained in Preparation Example 1 (accounting for about 0.08% of the waste acid mass), and stir and keep warm for 20 minutes at a speed of 120 rpm.

[0026] (2) The pretreated waste acid is introduced into a glass-lined reactor equipped with a high shear dispersion disk and an external magnetic cyclone circulation system. The temperature is maintained at 75°C. The stirring is turned on at low speed (70 rpm). Zinc powder with a particle size of 200 mesh is added. The amount added is 1.03 times the stoichiometric ratio required for theoretical replacement.

[0027] (3) Monitor the oxidation-reduction potential (ORP) of the reaction liquid in real time. The initial ORP is about -150mV. When the ORP drops to -380mV and the rate of drop slows down, immediately increase the stirring speed to 300rpm and simultaneously start the bottom circulation pump so that the reaction slurry enters the side circulation loop at a flow rate of 3 times the volume of the reactor per hour. In the circulation loop, the slurry first passes through a hydrocyclone with an inlet pressure of 0.20MPa and the underflow returns to the reactor. The overflow flows through a pipeline magnetic separator with a magnetic field strength of 4000Gauss. The iron powder is captured by the magnetic separator and the magnetically clear liquid returns to the reactor.

[0028] (4) When the circulating liquid ORP stabilizes at -500mV and the total iron content of the sampled solution is less than 40ppm, the reaction is stopped; the magnetic separator is demagnetized and backwashed with a small amount of clean water. The resulting slurry is filtered by plate and frame filter, washed with hot water at 60℃, and vacuum dried to obtain iron concentrate; the remaining liquid in the reactor is filtered to remove trace amounts of residual zinc powder, and the filtrate is then used in the next step.

[0029] (5) Add hydrogen peroxide to the filtrate (the amount added is 1.1 times the molar amount of residual ferrous ions) and adjust the pH to 5.0 to remove residual iron; then add lime milk with a mass fraction of 15% and adjust the pH to 9.0 to generate a white precursor slurry; pump the slurry into a hydrothermal reactor and react at 155°C and autogenous pressure for 4 hours; after the reaction is completed, centrifuge, wash and dry to obtain nano zinc oxide; the mother liquor of centrifugation is calcium chloride solution.

[0030] (6) Pump the calcium chloride mother liquor into a crystallization evaporator lined with polytetrafluoroethylene (PTFE), add 98% concentrated sulfuric acid (the molar ratio of sulfuric acid to calcium chloride is 1.02:1), control the reaction temperature at 140℃ and the system pressure at -0.03MPa; the hydrogen chloride (HCl) and water vapor produced by the reaction are recovered by a graphite condenser to obtain 19% hydrochloric acid; when the solid content of the slurry in the evaporator reaches 35%, it is centrifuged in a hot state, and the solid is calcium sulfate whiskers. The mother liquor is hot-recirculated back to the crystallization evaporator.

[0031] Example 2: This embodiment provides a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid, mainly verifying the lower limit of process parameters and the low-energy consumption mode, including the following steps: (1) Take 1000 kg of hot-dip galvanized waste acid (including 120 g / L ferrous chloride, 40 g / L zinc chloride, and 4% hydrochloric acid), heat it to 65°C, add 0.5 kg of the composite crystal plane guiding agent solution A obtained in Preparation Example 1 (about 0.05% of the waste acid mass), stir and keep warm for 15 minutes.

[0032] (2) Introduce waste acid into the reaction system, maintain the temperature at 70°C, stir at low speed (60 rpm), and add zinc powder (1.02 times the theoretical amount); when the ORP drops to -350 mV, switch to high shear mode and set the rotation speed to 250 rpm; open the circulation loop, set the hydrocyclone inlet pressure to 0.15 MPa, and set the magnetic field strength of the pipeline magnetic separator to 3000 Gauss.

[0033] (3) When the circulating liquid ORP stabilizes at -480mV and the total iron content is less than 50ppm, stop the reaction; collect iron concentrate according to the method in Example 1, and the filtrate proceeds to the next step.

[0034] (4) After the filtrate is oxidized and impurities are removed, the pH is adjusted to 8.5 with lime milk and pumped into a hydrothermal reactor. The reaction is carried out at 150°C for 3 hours. The subsequent treatment is the same as in Example 1 to obtain nano zinc oxide.

[0035] (5) The calcium chloride mother liquor was reacted with 98% concentrated sulfuric acid (molar ratio 1.01:1) at 135℃ and -0.02MPa and evaporated; hydrochloric acid was recovered by condensation and calcium sulfate whiskers were collected by centrifugation.

[0036] Example 3: This embodiment provides a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid, mainly verifying the upper limit of process parameters and the enhanced production mode, including the following steps: (1) Take 1000 kg of hot-dip galvanized waste acid (including 250 g / L ferrous chloride, 100 g / L zinc chloride, and 12% hydrochloric acid), heat it to 75°C, add 1.0 kg of the composite crystal plane guiding agent solution A obtained in Preparation Example 1 (about 0.1% of the mass of waste acid), stir and keep warm for 20 minutes.

[0037] (2) Introduce waste acid into the reaction system, maintain the temperature at 80°C, stir at low speed (80 rpm), and add zinc powder (1.05 times the theoretical amount); when the ORP drops to -400 mV, switch to high shear mode and set the rotation speed to 350 rpm; open the circulation loop, set the hydrocyclone inlet pressure to 0.25 MPa, and set the magnetic field strength of the pipeline magnetic separator to 5000 Gauss.

[0038] (3) When the circulating liquid ORP stabilizes at -520mV and the total iron content is less than 30ppm, stop the reaction; collect iron concentrate according to the method in Example 1, and the filtrate proceeds to the next step.

[0039] (4) After the filtrate is oxidized and impurities are removed, the pH is adjusted to 9.5 with lime milk and pumped into a hydrothermal reactor. The reaction is carried out at 165°C for 5 hours. The subsequent treatment is the same as in Example 1 to obtain nano zinc oxide.

[0040] (5) The calcium chloride mother liquor was reacted with 98% concentrated sulfuric acid (molar ratio 1.05:1) at 145℃ and -0.05MPa and evaporated; hydrochloric acid was recovered by condensation and calcium sulfate whiskers were collected by centrifugation.

[0041] Example 4: This embodiment provides a process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid, mainly verifying its adaptability to low-quality raw materials, including the following steps: (1) Take 1000 kg of hot-dip galvanized waste acid containing a lot of impurities (in addition to iron, zinc and acid, it also contains a small amount of manganese and lead impurities), heat it to 70°C, and add 0.8 kg of the composite crystal plane guiding agent solution A obtained in Preparation Example 1.

[0042] (2) The zinc source is zinc slag that has been ball-milled and sieved (zinc content 85%, particle size 100-200 mesh). The amount added is based on the effective zinc content and is 1.05 times the stoichiometric ratio required for theoretical replacement. The reaction process is maintained at 75℃. When the ORP drops to -380mV, the stirring speed is increased to 320rpm. The circulation loop is turned on and the magnetic field strength of the magnetic separator is set to 4500Gauss (to enhance the ability to capture iron powder in complex systems).

[0043] (3) The reaction endpoint control is the same as in Example 1; after collecting the iron concentrate, the filtrate proceeds to the next step.

[0044] (4) In the oxidation and impurity removal step of the filtrate, the amount of hydrogen peroxide is appropriately increased (1.2 times the theoretical amount), and the pH of impurity removal is strictly controlled to 5.2 to ensure co-precipitation to remove heavy metals such as lead; the subsequent hydrothermal synthesis of zinc oxide step is the same as in Example 1 (155℃, 4 hours).

[0045] (5) The acid regeneration steps are the same as in Example 1.

[0046] Example 5: This embodiment verifies the effect of different ratios of crystal plane guiding agents on the process, including the following steps: (1) Take 1000 kg of hot-dip galvanized waste acid (the composition is the same as in Example 1), heat it to 70°C, add 0.8 kg of the composite crystal plane guiding agent solution B (polyethylene glycol (PEG) ratio) obtained in Preparation Example 2, stir and keep warm for 20 minutes.

[0047] (2) The process parameters and operating methods of subsequent steps (2) to (6) are completely consistent with those of Example 1.

[0048] (3) This embodiment aims to investigate the effect of increasing the proportion of polyethylene glycol (PEG) on the crystal morphology of iron powder and the separation efficiency of cyclone magnetic separation.

[0049] Comparative Examples 1-6: Comparative Example 1: Compared with Example 1, the difference is that: in step (1), the composite crystal plane guiding agent solution A was not added, but an equal amount of deionized water was added; the remaining process steps and parameters are the same.

[0050] Comparative Example 2: Compared with Example 1, the difference is that the pipeline magnetic separator is removed in step (3), and the overflow liquid of the hydrocyclone is directly used as the product slurry for solid-liquid separation; the other process steps and parameters are the same.

[0051] Comparative Example 3: Compared with Example 1, the difference is that: in step (3), the stirring speed was not switched, and low-speed stirring (70 rpm) was maintained throughout the process, and the high-shear dispersion function was not turned on; the other process steps and parameters are the same.

[0052] Comparative Example 4: Compared with Example 1, the difference is that only polyethylene glycol 600 was added to the composite crystal plane guiding agent in step (1), and L-ascorbic acid was not added; the remaining process steps and parameters are the same.

[0053] Comparative Example 5: Compared with Example 1, the difference is that the method of preparing zinc oxide in step (5) is changed to the traditional calcination method, that is, after adjusting the pH to 9.0 to produce precipitation, it is directly filtered, dried, and placed in a muffle furnace to be calcined at 450°C for 2 hours to obtain zinc oxide; the remaining process steps and parameters are the same.

[0054] Comparative Example 6: Compared with Example 1, the difference is that: in step (3), ordinary stainless steel reactor and supporting pipelines are used, and glass-lined material and PTFE-lined equipment are not used; the other process steps and parameters are the same.

[0055] Test Examples 1-5: Test Example 1: Indirect Characterization of Microstructure of Iron Powder and Testing of Magnetic Separation Performance Experimental instructions and procedures: This test example aims to indirectly verify the regulatory effect of the crystal plane guiding agent on the growth of iron powder crystals and the separation efficiency of the high-shear, magnetic separation system in this invention by comparing the correlation between macroscopic physical indicators (bulk density) and chemical composition analysis (residual zinc content, iron recovery rate). Iron concentrates prepared in Examples 1-5 and Comparative Examples 1-4 were selected as test subjects.

[0056] Take 500g of iron powder samples from Examples 1 to 5 and Comparative Examples 1 to 4 after step (4), after plate and frame filtration and vacuum drying, and place them in a desiccator for later use.

[0057] According to the national standard GB / T1479.1-2011 (Determination of loose density of metal powders - Part 1: Funnel method), the loose density of each group of samples was determined using a Scott volumetric meter. Samples were naturally filled into a measuring cup of known volume, and the loose density was calculated by the ratio of mass to volume. Each group of samples was measured in triplicate, and the average value was taken. This index reflects the looseness and shape factor of the powder particles.

[0058] Weigh 5.00 g of each sample, completely digest with aqua regia, and then dilute to a volumetric flask with water to a final volume of 250 mL. The zinc (Zn) content in the solution was determined using inductively coupled plasma optical emission spectrometry (ICP-OES) to characterize the degree of zinc impurities in the iron powder (i.e., the severity of the iron-zinc encapsulation phenomenon).

[0059] Based on the total amount of waste acid iron during the feeding of each embodiment and comparative example, and the quality and grade of the final iron concentrate, the single-pass molar recovery rate of iron element was calculated.

[0060] Another sample from Comparative Example 2 (without magnetic separation) was used to conduct a simple adsorption test with an artificial magnet. The mass percentage of non-magnetic substances was recorded as auxiliary data.

[0061] Experimental data: Table 1. Test results of physical properties and separation index of iron powder products in each example and comparative example In the table, - indicates that it is not applicable.

[0062] Experimental conclusions and mechanism analysis: According to the data in Table 1, the loose bulk density of the iron powder obtained in Examples 1 to 5 is all distributed at 1.21 g / cm³. 3 Up to 1.42 g / cm 3 The density is significantly lower than the theoretical density of pure iron (7.87 g / cm³). 3 The bulk density of conventional spherical iron powder (usually greater than 2.5 g / cm³) and other similar materials. 3This physical indicator confirms the technical mechanism of the present invention: the steric hindrance effect formed by polyethylene glycol 600 (PEG-600) molecules at the reaction interface forces iron atoms to grow on the zinc surface in a non-layered manner, forming a highly loose dendritic or porous structure.

[0063] Comparing the data from Example 1 and Comparative Example 1, the product's bulk density reached as high as 2.87 g / cm³ without the addition of a crystal plane guiding agent. 3 Furthermore, the Zn content is as high as 18.64%. This indicates that under natural conditions, the iron generated by displacement tends to tightly coat the surface of zinc particles, forming a dense core-shell structure. This structure leads to two consequences: first, it hinders the contact between the internal zinc core and the external waste acid, causing premature passivation of the reaction and an iron recovery rate of only 82.3%; second, the iron and zinc are tightly bound, making physical methods unable to separate them, resulting in low product purity.

[0064] The data from Comparative Example 3 further revealed the coupling relationship between high shear and crystal plane orientation. Although an additive was added to Comparative Example 3, the loose packing density of its product decreased to 1.45 g / cm³. 3 (This proves that the crystal morphology has changed and the growth has become looser), but due to the lack of exfoliation effect from a high-shear flow field, the loose iron powder still adheres to the zinc core, resulting in a final product with a Zn content as high as 6.82% and a low recovery rate. This indicates that crystal morphology modification alone is insufficient to complete the separation; it must be combined with rheological field shear force to achieve the desorption of iron powder.

[0065] Comparative Example 2 data shows that if the magnetic separation step is cancelled, although the iron powder has a loose crystal structure and has been peeled (loose packing density 1.36 g / cm³), 3 Similar to Example 1), but because zinc powder and iron powder have similar densities, simple hydrocyclone cannot effectively distinguish between the two, resulting in a large amount of unreacted fine zinc powder being mixed into the product, and the Zn content rising to 12.55%.

[0066] In Example 5, increasing the PEG ratio further reduced the bulk density to 1.21 g / cm³. 3 This demonstrates that the surfactant concentration is positively correlated with the looseness of crystal growth, but the Zn content is not significantly better than that of Example 1, indicating that the ratio of Example 1 can meet the industrial separation requirements, and excessive addition does not bring about a qualitative change.

[0067] This invention modulates iron powder from a dense shell to loose dendrites using a crystal plane guiding agent, then achieves solid-solid exfoliation through a high-shear flow field, and finally utilizes magnetic differences for precise collection. This series of interconnected physicochemical processes, along with the differences in loose packing density and residual zinc content, fully validates the effectiveness and ingenuity of this technical approach.

[0068] Test Example 2: Verification Test of Negative Pressure Azeotropic Evaporation and System Water Balance Experimental instructions and procedures: This test case aims to verify the gas-liquid balance stability and water balance maintenance capability of step (6) (acid regeneration) in the process flow under continuous operation. By continuously monitoring the condensate composition and mass flow balance of multiple batches of reaction, the test evaluates whether negative pressure azeotropic distillation can effectively remove the reaction-generated water and the water introduced, preventing the malignant accumulation of mother liquor in the system.

[0069] A continuous experimental system was constructed using the process conditions of Example 1. The internal temperature of the crystallization evaporator was set at 140°C, and the absolute pressure of the system was maintained within the fluctuation range of -0.03 MPa to -0.035 MPa. Five reaction batches (Batch 1 to Batch 5) were run continuously. The mother liquor after centrifugation of the previous batch was directly refluxed to the next batch as the base liquid.

[0070] Accurately weigh the mass of calcium chloride mother liquor and concentrated sulfuric acid added in each batch, determine the moisture content of the raw materials, and calculate the total mass of water added.

[0071] During the reaction, the gaseous condensate is collected using a graphite condenser. After a single batch of reaction is completed (based on the solid content of the slurry in the reactor reaching a set threshold of 35%), the total mass of the collected condensate is weighed.

[0072] The mass fraction of hydrochloric acid in the condensate was determined by acid-base neutralization titration. Each batch of samples was measured in triplicate and the average value was taken.

[0073] The water removal rate for a single batch is calculated as the ratio of the mass of water in the condensate to the total mass of incoming water to assess whether the system is in a water balance state (ideally close to 100%).

[0074] As a comparison, a single atmospheric pressure evaporation experiment was run (set temperature 160℃, pressure 0MPa), and the composition of the condensate and the energy consumption time were recorded.

[0075] Experimental data: Table 2. Monitoring data of material balance and product composition of acid regeneration system under continuous batch operation. Experimental conclusions and mechanism analysis: According to the data in Table 2, Example 1 demonstrated extremely high stability during five consecutive batches of operation. The hydrochloric acid concentration in the condensate fluctuated steadily between 18.92% and 19.28%, a value highly consistent with the azeotropic composition characteristics of the hydrogen chloride-water system at -0.03 MPa pressure. In contrast, although the ambient pressure control group increased the temperature to 162.5°C, the recovered hydrochloric acid concentration was only 14.35%, and the processing time was extended by nearly 80%. This indicates that at ambient pressure, water tends to evaporate preferentially, making it difficult for HCl to be effectively removed, and the high-temperature environment exacerbates the corrosion risk and energy consumption burden of the equipment.

[0076] Regarding the verification of water balance, the average water removal rate from Batch 1 to Batch 5 remained around 98.8% (Batch 4 was slightly higher than 100% due to measurement error and the cumulative evaporation of trace dead volumes from the previous batch). This data confirms that the system has successfully established a dynamic balance between water inflow and outflow. In the metathesis reaction system of calcium chloride and concentrated sulfuric acid, the solvent water originates from the water introduced in the previous process and the water generated in the reaction. If this water and HCl cannot be removed simultaneously through azeotropic distillation, the volume of the mother liquor will expand exponentially with each cycle, ultimately leading to a decrease in the calcium chloride concentration and preventing the precipitation of calcium sulfate whiskers.

[0077] This invention utilizes negative pressure to lower the system's boiling point (from approximately 110°C at atmospheric pressure to about 75-85°C, but controlled at 140°C to ensure the growth kinetics of calcium sulfate whiskers and the anhydrous / hemihydrate conversion), enabling the gas-liquid interface to maintain a high-intensity mass transfer process. Data demonstrates that this process not only achieves high-value recovery of hydrochloric acid (approximately 19% concentration can be directly reused in the pickling line), but also solves the common problem of water balance bulging in all-wet processes, ensuring the full heat reflux of the mother liquor and achieving the goal of zero emissions.

[0078] Test Example 3: Comprehensive Comparison of Iron Concentrate Recovery Index and Reaction Kinetics Experimental instructions and procedures: This test case aims to quantitatively evaluate the differences in chemical purity, impurity content, and reaction kinetics of iron concentrate prepared under different process conditions. By comparing the key performance indicators of Examples 1 to 5 with Comparative Examples 1 to 4, the synergistic effect of chemical modification, high-shear exfoliation, and magnetic separation technologies in improving product quality and production efficiency is verified.

[0079] From the final products of Examples 1-5 and Comparative Examples 1-4, 200g of dried iron powder was extracted from each sample using the quartering method as the test sample; at the same time, the DCS record data of each batch of production process was retrieved to calculate the actual time taken from the addition of zinc powder to the reaction endpoint (ORP stabilization).

[0080] According to GB / T223 "Methods for Chemical Analysis of Iron and Steel and Alloys", the total iron content (TFe) in the sample is determined to characterize the purity of the main element of iron powder.

[0081] Weigh 1.000g of sample, digest it with a mixture of hydrochloric acid and nitric acid, and then use atomic absorption spectrometry (AAS) to determine the content of residual zinc (Zn) and impurities such as manganese (Mn) and lead (Pb); the zinc content directly reflects the solid-solid separation efficiency of the substitution product.

[0082] The determination of trivalent iron (Fe) in the sample was performed using the o-phenanthroline spectrophotometric method. 3+ ) content, calculate Fe 3+ The percentage of / TFe was used to quantitatively evaluate the antioxidant performance of iron powder during wet separation and drying processes.

[0083] Experimental data: Table 3. Comparison of Iron Concentrate Product Purity and Process Kinetic Parameters In the table, - indicates no special explanation.

[0084] Experimental conclusions and mechanism analysis: According to the data in Table 3, the total iron content (TFe) of the iron powder in Examples 1 to 5 remained stable between 96.92% and 98.42%, and the residual zinc content was controlled below 0.45%, indicating that the process system constructed in this invention has good robustness. Even in Example 4, which used high-impurity raw materials, the purity of the product still met the standard of industrial-grade iron concentrate, proving the process's adaptability to raw material fluctuations.

[0085] Comparing the reaction times of Example 1 (52 min) and Comparative Example 3 (92 min), it was found that the reaction time was extended by nearly 77% in the absence of a high shear flow field. The physical mechanism indicates that if the dendritic iron powder generated by the displacement reaction is not promptly removed, it will cover the zinc powder surface, forming a diffusion-restricting layer (passivation layer), hindering the interaction of Zn atoms with ferrous ions (Fe2+) in the solution. 2+ The contact between the reaction interface and the high-shear flow field in Example 1 not only accelerated the mass transfer process but also ensured the continuous reaction, thereby shortening the production cycle.

[0086] The differences between Comparative Example 1 and Comparative Example 2 reveal the respective contributions of chemical modification and magnetic separation. Although Comparative Example 2 underwent chemical modification (resulting in a looser crystal morphology), the removal of magnetic separation resulted in a TFe content of only 86.72% and a residual Zn content as high as 12.14%. This indicates that even with a loose iron powder morphology that detaches from the zinc surface, the density difference between the two is insufficient to support efficient hydrocyclone separation, necessitating the introduction of a magnetic field for physical capture. In contrast, Comparative Example 1, without both chemical modification and magnetic separation, saw a TFe content drop to 81.34% and experienced the longest reaction time (115 min), confirming that the negative impact of the encapsulation and passivation mechanisms is dual: both reducing the reaction rate and hindering solid-solid separation.

[0087] Furthermore, data from Comparative Example 4 show that although its TFe and Zn contents are similar to those of Example 1, Fe... 3+ The proportion was as high as 4.88%, higher than 0.45% in Example 1. This confirms the necessity of ascorbic acid (VC) in an acidic wet process environment. As a reducing agent, VC effectively inhibits the secondary oxidation of newly formed highly active iron powder during the filtration and drying stages, ensuring the metallic luster and chemical activity of the product.

[0088] The data in Table 3 fully demonstrate that this invention solves the technical problems of incomplete reaction and low product purity caused by iron-coated zinc in the traditional displacement method by using PEG to regulate crystal morphology, high shear strengthening kinetics, magnetic field to achieve precise separation, and VC to inhibit oxidation throughout the entire process control, thus achieving efficient and high-purity recovery of iron resources.

[0089] Test Example 4: Comparison of Physicochemical Properties and Microscopic Activity of Zinc Oxide Products Experimental instructions and procedures: This test aims to quantitatively evaluate the impact of different synthesis processes (hydrothermal crystallization and precipitation-calcination) on the final quality of zinc oxide products, focusing on the purity, optical properties (whiteness), and surface activity indicators (specific surface area and oil absorption value) of the products. Zinc oxide samples prepared in Examples 1 to 5 and Comparative Example 5 were selected as test subjects.

[0090] 100g of dried powder samples were randomly selected from the final batches of products from Examples 1-5 and Comparative Example 5 and placed in a constant temperature desiccator for equilibration for 24 hours.

[0091] According to the chemical industry standard HG / T2573-2012 "Industrial Active Zinc Oxide", the main content of zinc oxide (ZnO) was determined by the disodium ethylenediaminetetraacetate (EDTA) complexometric titration method; at the same time, the total content of trace metal impurities such as lead (Pb), cadmium (Cd), iron (Fe), and manganese (Mn) was determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0092] The R457 blue light whiteness value of the samples was determined using a WSB-2 whiteness meter. Before testing, standard black and white boards were used for calibration. The powder was pressed into a smooth, round disc, and each sample was tested three times at different locations, with the average value taken.

[0093] The specific surface area (SSA) of the samples was determined using a fully automated BET method with nitrogen as the adsorbate at a liquid nitrogen temperature (77 K). This indicator directly reflects the particle size and dispersion of powder particles.

[0094] According to GB / T 5211.15-2014 "General Test Methods for Pigments and Extenders - Part 15: Determination of Oil Absorption", dioctyl phthalate (DOP) was used as the oil absorption medium for manual titration. The volume of DOP required to wet 100g of sample was recorded to characterize the dispersibility of the powder and its compatibility with the organic matrix.

[0095] Experimental data: Table 4. Test results of physicochemical properties of zinc oxide products In the table, - indicates no special explanation.

[0096] Experimental conclusions and mechanism analysis: According to the data in Table 4, the nano zinc oxide prepared in Examples 1 to 5 of the present invention is superior to the traditional calcination product of Comparative Example 5 in all key indicators.

[0097] Firstly, regarding the microstructure, the BET specific surface area of ​​the samples in Examples 1-5 is distributed at 38.6 m². 2 / g to 48.1m 2 The oil absorption value remained at a high level of 46-55 mL / 100g. This indicates that the hydrothermal synthesis method, through a dissolution and recrystallization mechanism, promoted the controlled growth of the precursor in a liquid environment, forming well-dispersed, uniformly sized nanocrystals. In contrast, the BET value of Comparative Example 5 was only 18.2 mL / 100g. 2 / g, with an oil absorption value as low as 28.5mL / 100g. This is because during the high-temperature calcination of the precipitate precursor at 450℃, severe solid-phase sintering and necking effects occurred between the particles, causing the nanoparticles to agglomerate into large-sized hard aggregates, reducing the specific surface area and the number of surface active sites.

[0098] Secondly, regarding purity and optical properties, the ZnO purity in the example groups was all above 99.35%, and the whiteness value was generally higher than 94.9. This is due to the self-purification effect of the hydrothermal crystallization process, where impurity ions have difficulty entering the regularly arranged zinc oxide lattice, and most impurities are removed while remaining in the mother liquor. In contrast, the purity of Comparative Example 5 was only 98.15%, and the whiteness dropped to 88.4. This is because the precursor prepared by the precipitation method has an amorphous structure, which easily adsorbs or embeds impurity ions in the solution; in the subsequent high-temperature calcination stage, these impurities cannot be discharged and instead undergo oxidation and discoloration (such as the discoloration of trace manganese and iron oxides), resulting in a darker hue and a significant decrease in whiteness in the final product.

[0099] A comparison of data from Examples 2 and 3 reveals the kinetic effect of temperature on crystal growth: Example 3, with its higher temperature (165°C), exhibited enhanced Ostwald ripening, causing small grains to dissolve and recrystallize onto the surface of larger grains, resulting in an increased average grain size and thus a higher BET value (38.6 μm). 2 Example 2 (48.1m) was slightly below the low-temperature conditions ( / g). 2 / g). This adjustability demonstrates that the hydrothermal process can flexibly adjust product parameters according to downstream application requirements (such as high BET for rubber reinforcement and low BET for ceramic glazes).

[0100] The data in Table 4 confirms that the stepwise impurity removal + hydrothermal mineralization process adopted in this invention not only avoids the high energy consumption and dust pollution problems of traditional calcination methods, but also fundamentally improves the micro-dispersion and macro-cleanliness of the product from the perspective of crystal engineering, thus producing high-value-added active nano zinc oxide.

[0101] Test Example 5: Equipment Corrosion Resistance and Accumulated Impurity Introduction Test Experimental instructions and procedures: This test case aims to investigate the tolerance of the reaction equipment materials in the acid regeneration section to a high-temperature, high-acid, and high-chlorine system. By monitoring the cumulative concentration of characteristic alloying elements (nickel and chromium) in the circulating mother liquor and the color of the recovered acid, the stability of equipment made of different materials under long-term operation and their potential impact on product purity are evaluated. Example 1 (using PTFE-lined and glass-lined equipment) and Comparative Example 6 (using 316L stainless steel equipment) were selected as test objects.

[0102] Two parallel crystallization evaporation experimental apparatuses were constructed. Apparatus A corresponds to the material configuration of Example 1, with the vessel body being glass-lined and the pipelines and condenser interfaces lined with polytetrafluoroethylene (PTFE). Apparatus B corresponds to the material configuration of Example 6, with the vessel body, stirring paddle, and pipelines all made of 316L stainless steel.

[0103] Set the same process parameters: reaction temperature 140℃, system pressure -0.03MPa, and sulfuric acid dropping rate consistent with calcium chloride mother liquor reflux rate.

[0104] The continuous operation mode was started, and a total of 10 intermittent batches of evaporation and crystallization operations were carried out. After each batch, the calcium sulfate whiskers were separated by filtration, and the filtrate was directly returned to the reactor as the bottom liquid for the next batch. Only the consumed calcium chloride and sulfuric acid were replenished, simulating the closed-loop circulation process of mother liquor in industrial production.

[0105] 50 mL samples were taken from the centrifuged mother liquor after the reaction of batches 1, 3, 5, 7, and 10, respectively. After acidification with nitric acid, the concentrations of nickel (Ni) and chromium (Cr) in the samples were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). These two elements are characteristic alloying components of stainless steel and are used to indicate the degree of corrosion.

[0106] Collect the 10th batch of condensed hydrochloric acid solution, determine its color (Hazen units) using a platinum-cobalt colorimeter, and observe its appearance color.

[0107] Experimental data: Table 5. Cumulative concentrations of characteristic corrosive elements in circulating mother liquor and monitoring results of recovered acid quality In the table, - indicates no special explanation.

[0108] Experimental conclusions and mechanism analysis: According to the data in Table 5, in Example 1, during 10 consecutive batches of cyclic operation, the nickel (Ni) and chromium (Cr) content in the mother liquor remained at a low level (Ni < 0.15 mg / L, Cr < 0.15 mg / L), and the final recovered hydrochloric acid had a color of only 5 Hazen, exhibiting a colorless and transparent state. This indicates that the glass enamel and PTFE materials exhibit excellent chemical inertness in the high-temperature mixed acid environment at 140°C, completely blocking the migration path of impurities from the equipment materials to the reaction system, ensuring the long-term stable operation of the system and the high purity of the product.

[0109] In contrast, the data from Comparative Example 6 showed severe corrosion accumulation. Nickel and chromium were detected in the mother liquor starting from Batch 1; the corrosion rate accelerated non-linearly with increasing batch size. By Batch 10, the Ni content had surged to 245.80 mg / L, the Cr content reached 58.92 mg / L, and the recovered acid color reached a high of 180 Hazen, exhibiting a yellow-green hue.

[0110] Physicochemical mechanism analysis shows that in step (6) of this invention (acid regeneration step), in the ternary mixed system of calcium chloride, sulfuric acid, and water in a boiling state, although the main reaction generates volatile HCl, a high concentration of chloride ions (Cl-) is always present in the liquid phase. ) and hydrogen ions (H + At a high temperature of 140℃, high concentrations of Cl... It has strong penetrating power and can quickly destroy the dense chromium oxide passivation film on the surface of 316L stainless steel, forming pitting corrosion. The subsequent sulfuric acid medium further dissolves the iron and nickel in the substrate. This corrosion not only leads to safety accidents such as reactor perforation and leakage, but the dissolved heavy metal ions also accumulate continuously with the mother liquor circulation. Some of these ions enter the calcium sulfate whisker product, causing its whiteness to decrease and heavy metal content to exceed the standard. Others are carried into the recycled hydrochloric acid in the form of chloride, resulting in the deterioration of the hydrochloric acid quality, making it unusable for cleaning processes sensitive to impurities.

[0111] Table 5 confirms the necessity of using PTFE or glass-lined materials for the acid regeneration step in this invention. This is not only for equipment lifespan considerations, but also a key technical measure to cut off the source of impurity introduction and ensure the consistency of product quality throughout the entire process (iron powder, zinc oxide, calcium sulfate, and regenerated acid).

Claims

1. A process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid, characterized in that, Includes the following steps: The waste acid from hot-dip galvanizing is heated, and a composite crystal surface guiding agent solution is added. The mixture is kept at the temperature and stirred to obtain pretreated waste acid. The composite crystal surface guiding agent solution contains polyethylene glycol and ascorbic acid. The pretreated waste acid is introduced into the reaction system, and a zinc source is added under stirring conditions to carry out a displacement reaction; The redox potential of the reaction system is monitored in real time. When the redox potential drops to the first preset threshold, the high shear dispersion mode is activated, and the reaction slurry in the reaction system is introduced into an external circulation loop containing a magnetic separation device. The magnetic field is used to retain the iron powder, and the magnetically clear liquid is returned to the reaction system until the reaction endpoint is reached. The retained iron powder is washed and dried to obtain iron concentrate, and the remaining liquid in the reaction system after reaching the reaction endpoint is filtered to remove impurities, resulting in filtrate. Oxidizing agent and neutralizing agent are added to the filtrate to remove residual iron, pH value is adjusted to generate precursor slurry, hydrothermal reaction is carried out, and nano zinc oxide and calcium chloride mother liquor are obtained by solid-liquid separation. Concentrated sulfuric acid was added to the calcium chloride mother liquor, and a high-temperature evaporation and crystallization reaction was carried out under negative pressure. The regenerated hydrochloric acid was recovered by condensation, and the calcium sulfate whiskers were collected by centrifugation.

2. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The solute in the composite crystal plane guiding agent solution is composed of polyethylene glycol 600 and L-ascorbic acid, and the mass ratio of polyethylene glycol 600 to L-ascorbic acid is 1:1.2-1.2:1; The amount of the composite crystal plane guiding agent solution added is 0.05%-0.1% of the mass of the hot-dip galvanizing waste acid.

3. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The composite crystal plane guiding agent solution was prepared by the following method: Add deionized water to the mixing container and heat it to 30℃-40℃; First, add the polyethylene glycol 600 while stirring, and stir until clear and transparent; Then add the L-ascorbic acid, stir until completely dissolved, and cool to room temperature.

4. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The reaction temperature of the pretreated waste acid introduced into the reaction system is maintained at 70℃-80℃. The zinc source is zinc powder or ball mill zinc slag, and the amount added is based on the effective metallic zinc and is 1.02-1.05 times the stoichiometric ratio required for theoretical replacement.

5. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The first preset threshold is -350mV to -400mV, and the stirring speed after the high shear dispersion mode is turned on is 250rpm-350rpm.

6. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, A hydrocyclone is connected in series in the external circulation loop; The reaction slurry first enters the hydrocyclone for classification, the underflow is returned to the reaction system, and the overflow enters the magnetic separation device, which is a pipeline magnetic separator. The inlet pressure of the hydrocyclone is controlled at 0.15MPa-0.25MPa; the magnetic field strength of the inline magnetic separator is set at 3000Gauss-5000Gauss.

7. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The specific process for obtaining the nano-zinc oxide and calcium chloride mother liquor is as follows: The oxidant is added to the filtrate in an amount 1.1 to 1.2 times the molar amount of residual ferrous ions, and the pH is adjusted to 5.0 to 5.2 to precipitate and remove residual iron and heavy metal impurities. The neutralizing agent is then added to adjust the pH to 8.5-9.5 to generate the precursor slurry; The precursor slurry is pumped into a hydrothermal reactor and reacted at 150℃-165℃ under autogenous pressure for 3-5 hours, followed by solid-liquid separation. The oxidant is hydrogen peroxide, and the neutralizing agent is lime milk.

8. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The molar ratio of concentrated sulfuric acid to calcium chloride in the calcium chloride mother liquor is 1.01:1-1.05:1; The negative pressure condition is a system absolute pressure of -0.02 MPa to -0.05 MPa; The temperature of the high-temperature evaporation crystallization reaction is controlled at 135℃-145℃.

9. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The high-temperature evaporation crystallization reaction is carried out in a crystallization evaporation kettle lined with polytetrafluoroethylene or glass-lined material; The hydrogen chloride and water vapor produced in the reaction are condensed and recovered by a graphite condenser to obtain the regenerated hydrochloric acid with a mass concentration of 18%-20%. The high-temperature evaporation crystallization reaction adopts a continuous mother liquor circulation mode, in which the centrifuged mother liquor after collecting calcium sulfate whiskers from the previous batch is returned to the crystallization evaporation kettle as the bottom liquid for the next batch.

10. The process for preparing iron concentrate and high-purity zinc oxide from hot-dip galvanizing waste acid according to claim 1, characterized in that, The reaction equipment used in the process of carrying out the displacement reaction until the reaction endpoint is reached is a glass-lined reactor with a heating jacket, and the external circulation loop is lined with polytetrafluoroethylene.

Images