A method for deep purification of sulfuric acid for batteries

Abstract

The application discloses a deep impurity removal and purification method of sulfuric acid for storage batteries, and belongs to the technical field of purification of inorganic chemical products, and aims to solve the problems of easy introduction of exogenous metal cations, high risk of H2S diffusion, and insufficient simultaneous deep removal effect on Cu, Pb, As and Sb metal impurities in the existing sulfuric acid impurity removal method. The application uses SO2 reduction and value adjustment, load type phosphorus pentasulfide heterogeneous sulfidation impurity removal and filter membrane filtration separation coupling process, and realizes the simultaneous deep removal of various metal impurities without introducing metal-containing soluble reagents.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical product purification technology, specifically relating to a method for deep purification of sulfuric acid used in storage batteries. Background Technology

[0002] Lead-acid batteries have strict requirements regarding the content of metallic impurities in the sulfuric acid used as electrolyte. Trace amounts of Cu, As, and Sb impurities in a 4 mol / L sulfuric acid electrolyte environment with a Pb-Ca-Sn alloy grid will promote the disproportionation self-discharge reaction of the PbO2 layer, accelerating the capacity decay of the plates. Industrial sulfuric acid obtained from smelting flue gas typically contains residual Cu, Pb, As, and Sb, each with different chemical properties: Cu... 2+ and Pb 2+ It belongs to soft acid or boundary acid metal, and As and Sb exist as cations or oxygen-containing anions in different valence states.

[0003] Currently, the most commonly used purification method in industry is the sulfide precipitation method, which uses sodium sulfide or sodium hydrosulfide as the sulfiding agent. It utilizes the low solubility product of metal sulfides to achieve the co-precipitation and removal of Cu, Pb, and As, achieving a removal rate of 96%~98% for Cu and As. This method has the following drawbacks: Na... + The introduction of [this substance] constitutes secondary pollution to the cationic purity of battery-grade sulfuric acid; sulfide precipitation is a non-selective co-precipitation mechanism and cannot target As [substances / chemicals]. 5+ High-valence oxygen-containing anion impurities require efficient removal. Another commonly used method is lime / iron salt co-precipitation, where Ca(OH)₂ is added to the sulfuric acid containing impurities to neutralize it to pH 2-5, followed by the addition of iron salts and hydrogen peroxide to oxidize and precipitate arsenic. Arsenic removal rates can reach over 98%. However, this method requires a significant reduction in acidity, and the neutralization process introduces a large amount of Ca. 2+ It also produces gypsum residue, and the system after treatment is no longer pure sulfuric acid, so it cannot be directly used for the preparation of battery electrolyte.

[0004] In summary, there is an urgent need to develop a deep sulfuric acid purification method for batteries that is suitable for acidic sulfuric acid media, does not introduce metal-containing soluble reagents, can simultaneously and deeply remove multiple metal impurities such as Cu, Pb, As, and Sb, and is safe to operate. Summary of the Invention

[0005] This invention provides a deep purification method for sulfuric acid used in storage batteries, aiming to solve the problems of existing sulfuric acid purification methods, such as easy introduction of exogenous metal cations, high risk of H2S escape, and insufficient simultaneous deep removal of multiple metal impurities such as Cu, Pb, As, and Sb.

[0006] The specific technical solution is as follows: A method for deep purification of sulfuric acid for storage batteries includes the following steps: S1: SO2 / N2 mixed gas is introduced into the raw acid with a sulfuric acid concentration of 15wt% at a rate of 70mL / min. The reaction is carried out for 45 minutes at a reaction temperature of 40~55℃ and a stirring speed of 150~300rpm. As... 5+ Restore to As 3+ After the reaction is complete, purge the liquid with nitrogen for 10-15 minutes. S2: Add a supported phosphorus pentasulfide impurity removal material to the liquid obtained in step S1, and react for 120 minutes at a reaction temperature of 50-70°C and a stirring speed of 200 rpm to remove Cu from the liquid. 2+ Pb 2+ As 3+ and Sb 3+ The H2S released by the hydrolysis of the supported phosphorus pentasulfide impurity removal material reacts to form insoluble sulfide precipitates; the reacted liquid is then separated into solid and liquid phases by passing it through an acid-resistant filter membrane, and the resulting filtrate is purified sulfuric acid after deep impurity removal; the supported phosphorus pentasulfide impurity removal material includes a diatomaceous earth carrier that has been acid-washed and dried, and solid phosphorus pentasulfide attached to the surface and / or pores of the diatomaceous earth carrier, wherein the loading of solid phosphorus pentasulfide in the supported phosphorus pentasulfide impurity removal material is 15% to 40% of the mass of the diatomaceous earth carrier.

[0007] Furthermore, the raw material acid mentioned in step S1 is industrial sulfuric acid containing impurities obtained from the production of sulfuric acid from smelting flue gas.

[0008] Furthermore, the volume fraction of SO2 in the SO2 / N2 mixture in step S1 is 0.5 vol.

[0009] Further, in step S1, the total molar amount of SO2 introduced into the SO2 / N2 mixture is equal to the amount of As in the raw material acid. 5+ 1.5 to 2.5 times the molar amount.

[0010] Furthermore, the amount of the supported phosphorus pentasulfide impurity removal material added in step S2 is calculated based on its phosphorus pentasulfide content, which is equal to the Cu content in the feed solution. 2+ Pb 2+ As 3+ and Sb 3+ The total amount of H2S required for the theoretical precipitation of metal ions by sulfidation is 0.5 to 0.8 times the total molar amount of H2S.

[0011] Further, the preparation method of the supported phosphorus pentasulfide impurity removal material in step S2 includes carrier pretreatment, phosphorus pentasulfide loading, and solvent removal; the carrier pretreatment involves acid washing of calcined diatomaceous earth with sulfuric acid solution, washing with deionized water until the pH of the washing solution is ≥4, and drying to obtain an acid-washed diatomaceous earth carrier; the phosphorus pentasulfide loading involves adding phosphorus pentasulfide to anhydrous carbon disulfide under anhydrous nitrogen protection to prepare a phosphorus pentasulfide / carbon disulfide suspension dispersion, spraying the obtained phosphorus pentasulfide / carbon disulfide suspension dispersion in batches onto the acid-washed diatomaceous earth carrier, and allowing it to stand for aging to obtain a loaded sample; the solvent removal involves evaporating the carbon disulfide solvent from the obtained loaded sample under vacuum conditions to obtain the supported phosphorus pentasulfide impurity removal material.

[0012] Furthermore, the calcined diatomaceous earth has a mesh size of 200-400; the sulfuric acid solution has a concentration of 10 wt%; and the acid washing treatment conditions are: acid washing at 80°C for 2-4 hours.

[0013] Furthermore, the acid-washed diatomaceous earth carrier has a specific surface area of ​​40 m². 2 / g, pore volume 0.55mL / g.

[0014] Furthermore, the mass ratio of phosphorus pentasulfide to carbon disulfide in the phosphorus pentasulfide / carbon disulfide suspension is 1:(3~5).

[0015] Furthermore, the acid-resistant filter membrane mentioned in step S2 is made of polytetrafluoroethylene with a pore size of 5 μm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, phosphorus pentasulfide (P2S5) is loaded in thin layer form onto the surface and / or inner wall of a porous diatomaceous earth carrier, so that the hydrolysis and sulfidation reactions occur at the solid-liquid interface on the carrier surface or in the pores. This heterogeneous sulfidation interface structure effectively overcomes the surface passivation defect of incomplete hydrolysis of phosphorus pentasulfide blocks, while allowing the released H2S to be immediately consumed by metal ions in the confined space of the pores, significantly reducing the loss of H2S and improving operational safety and solid-liquid separation efficiency.

[0017] (2) In this invention, SO2 is used as a reducing agent to reduce As 5+ Selective reduction to As 3+ This valence state regulation process is completed in a pure acid system without introducing metal-containing soluble reagents, effectively ensuring the purity of the sulfuric acid cations used in storage batteries. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow for the deep sulfuric acid purification method for storage batteries according to the present invention. Figure 2These are scanning electron microscope images of the supported P2S5 impurity removal material and its carrier according to the present invention, wherein... Figure 2 (a) is a scanning electron microscope image of the acid-washed diatomaceous earth support prepared in Example 1. Figure 2 (b) is a scanning electron microscope image of the loaded P2S5 impurity removal material prepared in Example 1. Detailed Implementation

[0019] This invention proposes a method for deep purification of sulfuric acid used in storage batteries. Using 15wt% industrial sulfuric acid (obtained from smelting flue gas) as raw material, a coupled process of SO2 reduction and valence adjustment, supported P2S5 heterogeneous sulfidation for impurity removal, and membrane filtration separation is employed to achieve simultaneous deep removal of multiple metallic impurities, including Cu, Pb, As, and Sb. (See attached diagram.) Figure 1 The diagram shown is a schematic representation of the process flow of this invention.

[0020] Preparation of the supported P2S5 impurity removal material: (1) Carrier pretreatment: Take 200~400 mesh calcined diatomaceous earth and acid wash it with 10wt% sulfuric acid solution at 80℃ for 2~4 hours to dissolve residual Fe, Al and other metal oxide impurities in the carrier; after acid washing, wash with deionized water until the washing solution pH≥4, and dry at 120℃ for 4~6 hours to obtain a specific surface area of ​​40m². 2 Acid-washed diatomaceous earth carrier with a pore volume of 0.55 mL / g and a pore volume of 0.55 mL / g should be sealed and stored for later use.

[0021] (2) P2S5 loading: Under anhydrous nitrogen protection, industrial-grade P2S5 (purity ≥98%) was added to anhydrous carbon disulfide (CS2) and ultrasonically dispersed to prepare a P2S5 / CS2 suspension. The mass ratio of P2S5 to CS2 in the P2S5 / CS2 suspension was 1:(3~5). The P2S5 / CS2 suspension was slowly sprayed in batches onto the above-mentioned acid-washed diatomaceous earth carrier, and the carrier was stirred evenly after each spray. After loading, the sample was aged at 25~30℃ under a nitrogen atmosphere for 2~4 hours.

[0022] (3) Solvent removal: The aged sample is transferred to a vacuum drying oven and the CS2 solvent is removed by evaporation at 40~50℃ and a vacuum degree of not less than 0.09MPa for 4~8 hours. The resulting solid powder is the supported P2S5 impurity removal material, wherein the P2S5 loading is 15%~40% of the carrier mass. The obtained material is stored in a dry sealed container under nitrogen protection.

[0023] The present invention provides a method for deep purification of sulfuric acid for storage batteries, comprising the following specific steps: S1.SO2 Reduction and Price Adjustment Processing An industrial-grade SO2 / N2 mixture is introduced into the raw acid. The volume fraction of SO2 in the mixture is 0.5 vol%. The total molar amount of SO2 introduced is equal to the amount of As in the raw acid. 5+ The molar amount is 1.5 to 2.5 times that of As, and the flow rate is controlled at 70 mL / min. The reaction is carried out at 50℃ and a stirring speed of 200 rpm for 45 minutes. SO2 in acidic medium reacts with As. 5+ Selective reduction to As 3+ As 3+ The solubility product of As₂S₃ is much lower than that of As. 5+ The presence of oxygen-containing precipitates significantly enhances the removal depth of As in subsequent sulfidation steps. After SO2 is introduced, excess dissolved SO2 is removed by purging with nitrogen for 10-15 minutes, and the solution proceeds to the next step of processing.

[0024] S2. Loaded P2S5 heterogeneous sulfurization for impurity removal The above-prepared supported P2S5 impurity removal material is added to the feed solution after S1 treatment. The amount added is calculated based on the phosphorus pentasulfide content in the feed solution as Cu. 2+ Pb 2+ As 3+ and Sb 3+ The total molar amount of H2S required for the theoretical precipitation of metal ions by sulfidation is 0.5 to 0.8 times the total molar amount of H2S. The reaction is carried out at 50–70°C and a stirring rate of 200 rpm for 120 minutes. During the reaction, P2S5 comes into contact with water in the sulfuric acid medium at the solid-liquid interface on the support surface or in the pores, generating sulfur-containing active species including H2S, polysulfides, and phosphorus-sulfur species. These sulfur-containing active species react with Cu in the feed solution within the confined space on the support surface or in the pores. 2+ Pb 2+ As 3+ and Sb 3+ Metal ions undergo a sulfidation precipitation reaction to generate a sulfur-containing insoluble solid phase, which is mainly deposited, adsorbed, or embedded on the surface and inner wall of the porous carrier.

[0025] After the reaction, the feed solution is filtered through a 5μm pore size acid-resistant membrane to separate the carrier particles and the attached metal sulfide precipitates. The acid-resistant membrane is a polytetrafluoroethylene (PTFE) membrane. Because the sulfide precipitates adhere to the surface and pores of the carrier particles, the filtration efficiency is significantly better than that for traditional separation of fine colloidal sulfide particles. The filtrate is purified sulfuric acid after deep impurity removal, which can be further evaporated and concentrated according to product concentration requirements. The filtered carrier and its loaded metal sulfide precipitates are collected and treated as heavy metal-containing solid residues. When the carrier needs to be reused, it can be reloaded with P2S5 after controlled acid washing, oxidation cleaning, water washing, and drying. The cleaning wastewater is centrally disposed of as heavy metal-containing wastewater.

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] The preferred embodiments of the present invention are described in detail below; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

[0028] Example 1 The raw material acid is 1000g (15wt%) of industrial sulfuric acid obtained from smelting flue gas containing impurities: approximately 18mg (0.283mmol) of Cu; approximately 12mg (0.0579mmol) of Pb; and approximately 25mg (0.334mmol) of As. 5+ The main component is Sb, approximately 8 mg (0.0657 mmol).

[0029] Supported P2S5 impurity removal material: 300-mesh calcined diatomaceous earth was acid-washed with a 10wt% sulfuric acid solution at 80℃ for 3 hours; after acid washing, it was washed with deionized water until the washing solution pH≥4, and dried at 120℃ for 5 hours to obtain a specific surface area of ​​40m². 2 Acid-washed diatomaceous earth carrier with a pore volume of 0.55 mL / g was prepared. 10 g of acid-washed diatomaceous earth carrier was mixed with 2.0 g (9.0 mmol) of P2S5 under nitrogen protection and added to 8.0 g of anhydrous CS2 to prepare a P2S5 / CS2 suspension. The P2S5 / CS2 suspension was sprayed evenly onto the diatomaceous earth carrier in three separate applications. After aging at 25°C under a nitrogen atmosphere for 3 hours, the carrier was dried at 45°C under a vacuum of 0.09 MPa for 6 hours to obtain a supported P2S5 impurity removal material. The P2S5 loading was 20% of the carrier mass.

[0030] (1) Industrial-grade SO2 / N2 mixed gas was introduced into the raw acid at a rate of 70 mL / min. The volume fraction of SO2 was about 0.5 vol%, and the total amount of SO2 introduced was about 0.045 g (0.703 mmol). The gas was continuously introduced and the reaction was maintained at 50 °C and a stirring rate of 200 rpm for 45 minutes. After the gas introduction was completed, nitrogen gas was introduced into the liquid to purge for 12 minutes.

[0031] (2) Cu in the feed solution 2+ Pb 2+ As3+ and Sb 3+ The theoretical total molar amount of H2S required for the sulfidation precipitation of metal ions is 0.941 mmol. 0.63 g (0.567 mmol) of the above-mentioned supported P2S5 impurity removal material was added to the solution obtained in (1), and the reaction was carried out at 60 °C and a stirring rate of 200 rpm for 120 minutes. After the reaction was completed, the solution was filtered through a 5 μm pore size polytetrafluoroethylene membrane, and the collected filtrate was the purified sulfuric acid product.

[0032] Example 2 The process conditions were the same as in Example 1, except that the P2S5 loading in the supported P2S5 impurity removal material was adjusted to 15wt%, and the amount of impurity removal material added was increased to 0.84g (0.567mmol) to keep the molar amount of P2S5 constant. The parameters of the other steps remained unchanged.

[0033] Example 3 The process conditions were the same as in Example 1, except that the P2S5 loading in the supported P2S5 impurity removal material was adjusted to 40wt%, and the amount of impurity removal material added was reduced to 0.32g (0.567mmol) to keep the molar amount of P2S5 constant. The parameters of the other steps remained unchanged.

[0034] Example 4 The process conditions are the same as in Example 1, except that the molar ratio of sulfurization in step (2) is adjusted from 0.6 times to 0.5 times, and the amount of loaded P2S5 impurity removal material is adjusted accordingly to 0.52g (0.468mmol). The parameters of the other steps remain unchanged.

[0035] Example 5 The process conditions are the same as in Example 1, except that the molar ratio of sulfurization in step (2) is adjusted from 0.6 times to 0.8 times, and the amount of loaded P2S5 impurity removal material is adjusted accordingly to 0.84g (0.756mmol). The parameters of the other steps remain unchanged.

[0036] Example 6 The process conditions are the same as in Example 1, except that the vulcanization reaction temperature in step (2) is adjusted from 60°C to 50°C, while the parameters of the other steps remain unchanged.

[0037] Example 7 The process conditions are the same as in Example 1, except that the vulcanization reaction temperature in step (2) is adjusted from 60°C to 70°C, while the parameters of the other steps remain unchanged.

[0038] Comparative Example 1 The process conditions were the same as in Example 1, except that the supported P2S5 impurity removal material was replaced by directly adding 0.138g of bulk P2S5 powder to the liquid, and the reaction was carried out at 60°C and 200rpm for 120 minutes. The parameters of the other steps remained unchanged.

[0039] Comparative Example 2 The raw acid was treated using the traditional sulfide precipitation method: 1000g of the same raw acid as in Example 1 was taken, and 0.68g (2.82mmol) of sodium sulfide nonahydrate was added directly to the raw acid. The reaction was carried out at 60°C and a stirring rate of 200rpm for 120 minutes. After the reaction was completed, the solution was filtered through a 5μm pore size filter membrane and the filtrate was collected.

[0040] Comparative Example 3 The process conditions are the same as in Example 1, except that the SO2 reduction and valence adjustment step is omitted, while the parameters of the other steps remain unchanged.

[0041] Product Testing 1. Determination of residual concentration of metallic impurities The final products of each embodiment and comparative example were appropriately diluted with deionized water, and the residual concentrations (mg / kg) of Cu, Pb, As, and Sb in the filtrate and the corresponding removal rates (%) were determined by inductively coupled plasma atomic emission spectrometry. Each group of samples was measured in triplicate, and the average value was taken. The removal rate was calculated using the following formula: Removal rate (%) = (Initial mass concentration - Residual mass concentration) / Initial mass concentration × 100%.

[0042] 2. Determination of peak concentration of hydrogen sulfide emission Step (2) of each embodiment, Comparative Example 2, Comparative Example 3, and the bulk P2S5 addition step of Comparative Example 1 were all carried out in a sealed reactor of the same specifications. A gas sampling port was set at the top of the reactor, and the exhaust port was connected to an activated carbon adsorption tail gas treatment device. Throughout the reaction, the gas phase H2S concentration was sampled and recorded every 10 minutes at the gas sampling port at the top of the reactor using an electrochemical portable hydrogen sulfide gas detector (range 0~100ppm, accuracy 0.1ppm). The highest reading throughout the process was taken as the peak concentration of H2S escaping (ppm).

[0043] 3. Determination of filtrate turbidity After filtration, the products of each embodiment and comparative example were allowed to stand for 30 minutes. The supernatant was then taken and the turbidity value (NTU) was measured at room temperature using a turbidimeter based on the light scattering method. Each group was measured in parallel three times, and the average value was taken.

[0044] Scanning electron microscopy (SEM) characterization (1) Testing process: The acid-washed diatomaceous earth carrier powder prepared according to Example 1 was used as... Figure 2(a) The test sample was prepared according to Example 1 using the supported P2S5 impurity removal material powder. Figure 2 (b) The test samples. The powder of each sample was evenly dispersed on the surface of the conductive carbon tape, and loose, unadhered particles were blown away with a bulb syringe. Before testing, the surface of each sample was sputtered with gold to enhance conductivity; the gold sputtering thickness was approximately 5 nm. The morphology of each sample was observed using a scanning electron microscope at an accelerating voltage of 5 kV, a working distance of approximately 10 mm, and secondary electron imaging mode. The magnification was based on a scale bar of 2 μm. At least three different regions of each sample group were photographed, and representative images were recorded.

[0045] (2) Results analysis: see attached Figure 2 As shown, Figure 2 (a) shows the surface morphology of the acid-washed diatomite carrier prepared in Example 1. It can be seen that the diatom skeleton structure is completely preserved, the nanopores on the surface of the disk are arranged regularly and orderly, the pore size is uniformly distributed, the pore walls are clean and smooth, and the internal cavities of the pores are deep, dark and clear, without any external attachments, reflecting the effective exposure of the active sites on the carrier surface by the acid washing pretreatment. Figure 2 (b) shows the surface morphology of the supported P2S5 impurity removal material prepared in Example 1, compared with... Figure 2 (a) In contrast, the disc-shaped porous structure of the diatom skeleton is completely preserved. The outline of the skeleton and the geometric arrangement of the pores are highly consistent with the acid-washed diatomite carrier. There is no skeleton breakage, pore collapse or layer peeling. This proves that the anhydrous suspension dispersion loading and low-temperature vacuum desolvation process used in this invention has good gentleness on the carrier structure. At the same time, nano-sized fine particles of deposits are sparsely dispersed and attached on the surface of the disc and the inner wall of the pores. A large number of pore wall exposed areas are left between the particles. Most of the pores are still open. This proves that P2S5 is distributed in a thin layer of sparse loading form on the inner wall of the carrier pores without filling or blocking the pores. This provides sufficient diffusion channels for the solid-liquid interface contact between the feed liquid and the P2S5 active phase in the subsequent sulfurization reaction.

[0046] Table 1. Residual concentration and removal rate of metal impurities in the filtrate after treatment in each example and comparative example. ; Table 2. Peak H2S concentration and filtrate turbidity of each example and comparative example. ; Results analysis: (1) As shown in Tables 1 and 2, the removal rates of Cu, Pb, As, and Sb target impurities in Examples 1 to 7 were all at a high level, while the peak concentration of H2S escaping and the turbidity of the filtrate were at a low level, and the overall indicators were excellent. Among them, Example 1 had the best indicators under the optimal process conditions. In Example 2, due to the lower limit of P2S5 loading, the density of effective sulfur components in the pores decreased, and the removal depth of Cu, As, and Sb was slightly lower than that in Example 1. In Example 3, the loading was at the upper limit, and the dense filling of the active phase in the pores slightly inhibited the utilization rate of the slow-release interface, and the removal depth was also slightly lower than that in Example 1. In Example 4, the molar amount of sulfide was at the lower limit, and the removal depth of As and Sb was more sensitive to insufficient molar amount of sulfide than that of Cu and Pb. In Example 5, the molar amount of sulfide was at the upper limit, and the removal depth was comparable to that in Example 1. In Example 6, the sulfide temperature was at the lower limit, the hydrolysis rate of P2S5 slowed down, and the removal depth of Cu, As, and Sb decreased slightly. In Example 7, the sulfide temperature was at the upper limit, the hydrolysis rate accelerated, and the removal depth was close to that in Example 1. In summary, the method of the present invention has a stable and reliable purification effect within the range of the stated process parameters.

[0047] (2) In Comparative Example 1, after replacing the loaded P2S5 impurity removal material with an equal amount of bulk P2S5, the removal depths of Cu, Pb, As, and Sb were significantly lower than those in the other examples. As shown in Table 2, the peak concentration of H2S escaping in Comparative Example 1 increased significantly, and the turbidity of the filtrate was significantly higher. The main reason for this was that the H2S release from the bulk P2S5 was not constrained by the pores due to surface hydrolysis and passivation, resulting in a decrease in effective utilization. At the same time, the generated fine colloidal sulfide precipitates were difficult to filter and retain effectively. Comparative Example 2 used the traditional sodium sulfide process, and its As residue and filtrate turbidity were significantly higher. The main reason for this was that the process was not efficient enough in removing high-valence As by sulfidation.

[0048] (3) After omitting the SO2 reduction and adjustment step in Comparative Example 3, the residual As content was significantly higher, while the removal depth of other impurities was comparable to that of each example. This indicates that high-valence As cannot form low-solubility-product sulfide precipitates in an acidic system without valence state regulation. The SO2 reduction and adjustment step plays a decisive role in the deep removal of arsenic.

[0049] In summary, this invention achieves simultaneous and deep removal of multiple metallic impurities such as Cu, Pb, As, and Sb from industrial sulfuric acid through a coupled process of SO2 reduction and valence adjustment and supported P2S5 heterogeneous sulfidation for impurity removal. The entire process maintains a pure acidic system and does not introduce metal-containing soluble reagents, providing a safe and clean purification method for the preparation of high-purity sulfuric acid for storage batteries.

Claims

1. A method for deep purification of sulfuric acid for storage batteries, characterized in that, Includes the following steps: S1: A SO2 / N2 mixture is introduced into a 15wt% sulfuric acid feedstock at a rate of 70 mL / min. The reaction is carried out for 45 minutes at a reaction temperature of 40–55℃ and a stirring speed of 150–300 rpm. As… 5+ Restore to As 3+ After the reaction is complete, purge the feed liquid with nitrogen for 10-15 minutes; the volume fraction of SO2 in the SO2 / N2 mixture is 0.5 vol%; the total molar amount of SO2 introduced into the SO2 / N2 mixture is equal to the amount of As in the feed acid. 5+ 1.5 to 2.5 times the molar amount; S2: Add a supported phosphorus pentasulfide impurity removal material to the liquid obtained in step S1, and react for 120 minutes at a reaction temperature of 50-70°C and a stirring speed of 200 rpm to remove Cu from the liquid. 2+ Pb 2+ As 3+ and Sb 3+ The H2S released during the hydrolysis of the supported phosphorus pentasulfide impurity removal material reacts to form insoluble sulfide precipitates; the reacted solution is then subjected to solid-liquid separation through an acid-resistant filter membrane, and the resulting filtrate is purified sulfuric acid after deep impurity removal; the supported phosphorus pentasulfide impurity removal material comprises a diatomaceous earth carrier that has undergone acid washing and drying treatment, and solid phosphorus pentasulfide attached to the surface and / or pores of the diatomaceous earth carrier, wherein the loading of solid phosphorus pentasulfide in the supported phosphorus pentasulfide impurity removal material is 15% to 40% of the mass of the diatomaceous earth carrier; The preparation method of the supported phosphorus pentasulfide impurity removal material includes carrier pretreatment, phosphorus pentasulfide loading, and solvent removal. The carrier pretreatment involves acid washing of calcined diatomaceous earth with sulfuric acid solution, washing with deionized water until the pH of the washing solution is ≥4, and drying to obtain an acid-washed diatomaceous earth carrier. The phosphorus pentasulfide loading involves adding phosphorus pentasulfide to anhydrous carbon disulfide under anhydrous nitrogen protection to prepare a phosphorus pentasulfide / carbon disulfide suspension dispersion, wherein the mass ratio of phosphorus pentasulfide to carbon disulfide is 1:(3~5). The obtained phosphorus pentasulfide / carbon disulfide suspension dispersion is sprayed in batches onto the acid-washed diatomaceous earth carrier and allowed to stand for aging to obtain the loaded sample. The solvent removal involves evaporating the carbon disulfide solvent from the obtained loaded sample under vacuum conditions to obtain the supported phosphorus pentasulfide impurity removal material.

2. The method for deep purification of sulfuric acid for storage batteries as described in claim 1, characterized in that, The raw material acid mentioned in step S1 is industrial sulfuric acid containing impurities, obtained from the production of sulfuric acid from smelting flue gas.

3. The method for deep purification of sulfuric acid for storage batteries as described in claim 1, characterized in that, The amount of the supported phosphorus pentasulfide impurity removal material added in step S2 is calculated based on its phosphorus pentasulfide content, which is equal to the Cu content in the feed solution. 2+ Pb 2+ As 3+ and Sb 3+ The total amount of H2S required for the theoretical precipitation of metal ions by sulfidation is 0.5 to 0.8 times the total molar amount of H2S.

4. The method for deep purification of sulfuric acid for storage batteries as described in claim 1, characterized in that, The calcined diatomaceous earth has a mesh size of 200-400 mesh; the sulfuric acid solution has a concentration of 10 wt%; and the acid washing conditions are: acid washing at 80°C for 2-4 hours.

5. The method for deep purification of sulfuric acid for storage batteries as described in claim 1, characterized in that, The acid-washed diatomaceous earth carrier has a specific surface area of ​​40m². 2 / g, pore volume 0.55mL / g.

6. The method for deep purification of sulfuric acid for storage batteries as described in claim 1, characterized in that, The acid-resistant filter membrane mentioned in step S2 is made of polytetrafluoroethylene with a pore size of 5 μm.

Images