Method for treating and recycling iron-containing waste sulfuric acid generated in titanium dioxide production process

Abstract

The invention provides a method for treating and recycling iron-containing waste sulfuric acid in titanium dioxide production, which is a method for treating iron-containing waste sulfuric acid on the basis of screening strains for treating iron-containing waste water in a low-pH environment, and can effectively realize resource recycling. The used wastewater treatment bacterium is a bacillus QD-QJ-062 strain, and the preservation number of the bacillus QD-QJ-062 strain is CGMCC (China General Microbiological Culture Collection Center) No. 33725. The screened bacillus QD-QJ-062 strain can be used for effectively treating iron-containing wastewater in a low-pH environment, the generation of ferrous oxalate precipitate is promoted, and a ferrous oxalate byproduct is generated. The generated ferrous oxalate can be converted into ferrous sulfate through sulfuric acid, oxalic acid is recycled, the operation cost is reduced, the sulfuric acid solution subjected to iron removal can be neutralized through limestone, high-purity gypsum is generated, and resource recycling treatment is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental pollution treatment and resource utilization, and particularly relates to a treatment and resource utilization method for iron-containing waste sulfuric acid generated in a titanium dioxide production process. BACKGROUND

[0002] Titanium dioxide is a commonly used white pigment, which is widely used in the fields of coatings, plastics, papermaking, printing, etc. China has become the largest titanium dioxide producing country in the world. The production process of titanium dioxide mainly uses the sulfuric acid method, and uses titanium concentrate, high-titanium slag or titanium-rich materials as the main raw material to produce titanium dioxide with sulfuric acid. The industrial process is called the sulfuric acid method. The wastewater generated in the production process has the characteristics of large amount, high acidity, high suspended solids and high divalent iron content. The National Hazardous Waste List (2025 edition) HW34 waste acid 264-013-34 provides that "waste acid generated in the process of producing titanium dioxide (titanium dioxide) by the sulfuric acid method is a hazardous waste, and the hazardous characteristic is C, T". If the wastewater generated in the production of titanium dioxide is not effectively treated, it will cause serious damage to the ecological environment and waste of sulfuric acid.

[0003] The sulfuric acid method for producing titanium dioxide mainly includes processes such as acidolysis, hydrolysis, water washing and bleaching. The wastewater mainly comes from the water or sulfuric acid added in these processes, mainly containing H + and SO4 2- , accompanied by Fe 2+ , Ti 3+ , Cr 2+ , Mg 2+ , etc.

[0004] The conventional treatment process is generally first neutralized with lime or electric lime, aerated, and then separated by sedimentation to realize mud-water separation. The mud is made into gypsum after pressure filtration, and the filtrate is further treated to meet the discharge standard. The neutralization treatment has the advantages of low investment and simple operation, but the metal ions and other impurities in the waste sulfuric acid are easily left in the by-products, which can easily cause secondary pollution to the environment and is not conducive to the secondary utilization of the by-products. At the same time, the by-products such as gypsum are mainly used to produce low-end building materials by physical methods. Due to the limitation of market capacity and product sales radius, it is difficult to large-scale absorb the large amount of gypsum produced by neutralization. The construction of a storage yard is mainly used to store the gypsum, which has a large investment, occupies land, wastes sulfur-calcium resources, and affects public safety. At present, the environmental protection pressure is large, and no new storage yard is approved. The industrial by-product gypsum is washed away by rainwater, and the soluble harmful substances are dissolved in water, which can seriously pollute surface water and groundwater through system circulation. At the same time, the gypsum is scattered in the air in the form of powder and settled on the surface of objects after being blown by the wind and exposed to the sun, which not only pollutes the environment but also threatens health.

[0005] Therefore, existing treatment processes do not effectively utilize the acid in waste acid, and the resulting gypsum is difficult to utilize, thus failing to effectively achieve resource utilization. Developing new wastewater treatment processes for titanium dioxide production can shift the treatment of titanium dioxide wastewater from "end-of-pipe treatment" to "resource recycling," thereby simultaneously achieving environmental and economic benefits. Summary of the Invention

[0006] This invention provides a method for treating iron-containing waste sulfuric acid in titanium dioxide production. Based on the screening of strains that can treat iron-containing wastewater in a low pH environment, a method for treating iron-containing waste sulfuric acid is established, which can effectively realize resource recycling and reuse, thereby making up for the shortcomings of the existing technology.

[0007] This invention first provides a wastewater treatment bacterium, namely Bacillus (Bacillus). Bacillus sp Strain QD-QJ-062 was deposited on March 6, 2025, at the China General Microbiological Culture Collection Center (CGMCC), with accession number CGMCC No. 33725; the deposit address is the Institute of Microbiology, China, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing.

[0008] The present invention also provides an application of the aforementioned Bacillus in the treatment of acidic wastewater.

[0009] As a specific example, the acidic wastewater mentioned is iron-containing acidic wastewater generated during the production of titanium dioxide.

[0010] In another aspect, the present invention provides a method for treating iron-containing waste sulfuric acid wastewater from titanium dioxide production, wherein the method uses the aforementioned Bacillus ( Bacillus sp .) Strain QD-QJ-062 was used in the treatment.

[0011] Furthermore, the method includes the following steps: 1) Add the wastewater to be treated to the reaction tank, and then add oxalic acid and the above-mentioned Bacillus ( ). Bacillus sp .) strain QD-QJ-062, reacted to produce a treatment solution containing ferrous oxalate precipitate; 2) The treated liquid from 1) is introduced into a thickening tank for concentration to obtain concentrated liquid and clarified liquid; 3) The concentrate enters the primary sedimentation tank and the secondary sedimentation tank. The ferrous oxalate precipitate obtained from sedimentation is added to the filter press for solid-liquid separation to obtain a high-purity ferrous oxalate byproduct. The filter water is combined with the clarified liquid obtained in 2). 4) The combined wastewater is adsorbed using chelating resin LG-701 to further remove iron ions from the wastewater and obtain a high-purity sulfuric acid solution. 5) limestone slurry is added to the sulfuric acid solution to produce a pure calcium sulfate byproduct, and the pH of the wastewater is brought to the range of 6-8 for reuse.

[0012] Further, the method, wherein the inoculation amount of the Bacillus QD-QJ-062 strain is 10 6 CFU / mL; and the mass-volume percentage of the added oxalic acid is 6%.

[0013] The QD-QJ-062 strain of the screened Bacillus genus used in the present application can effectively treat iron-containing wastewater in a low-pH environment, promote the precipitation of ferrous oxalate, and generate a ferrous oxalate byproduct. The generated ferrous oxalate can also be converted into ferrous sulfate by sulfuric acid, and oxalic acid can be recovered, thereby reducing the operating cost. The sulfuric acid solution after iron removal can be neutralized by limestone to generate high-purity gypsum (CaSO4), thereby achieving resource recycling and treatment. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 : Acidic iron-containing wastewater treatment process flowchart, ①: discharge port ②: reaction conveying belt ③: reaction tank ④: control valve ⑤: liquid storage tank ⑥: conical flask ⑦: circulating water vacuum pump; Figure 2 : Acidic wastewater treatment process diagram, A is the water sample before treatment of the acidic iron-containing wastewater, and B is the precipitate generated after the addition of oxalic acid and the Bacillus QD-QJ-062 strain. DETAILED DESCRIPTION

[0015] The present application will be described in detail below in conjunction with examples and drawings.

[0016] Example 1: Screening of acid-resistant strains 1. Preliminary screening of strains In March 2024, sewage and bottom sludge samples (pH 3.5-4.0) were collected from a sewage channel in the Chengyang Industrial Park of Qingdao. The sewage channel has been receiving acidic wastewater from a nearby stainless steel foundry (containing sulfuric acid) for a long time. After the samples were filtered with filter paper, 10-10 4 fold gradient dilution was performed using a pH 4.0 phosphate buffer.

[0017] Culture medium formula (pH 3.5): 10 g of proteose peptone, 5 g of yeast extract, 10 g of NaCl, 15 g of agar, citric acid-disodium hydrogen phosphate buffer (pH 3.5), and distilled water to make up to 1 L. 100 µL of each gradient dilution was spread on acidic LB plates. Incubation was performed at 14℃ for 96 h. The colony morphology was observed, and single colonies were picked for pH 2.5-4.0 gradient acid resistance testing. A total of 45 strains that could grow in a pH 3.5 environment were isolated. Among them, 23 strains could still grow (OD 600>0.3) in a pH 3.0 environment.

[0018] 2. Spore formation ability screening Spore induction medium (pH 4.0): nutrient broth 8 g, MnSO4·H2O 0.01 g, CaCl2 0.1 g, citric acid buffer (pH 4.0), distilled water 1 L. 23 acid-tolerant strains were inoculated into the spore induction medium and cultured at 30°C with 180 rpm shaking for 48 h. 1 mL of the bacterial solution was taken and incubated in a water bath at 80°C for 10 min, then spread on LB plates at pH 4.0 and incubated at 25°C for 48 h, and the viable colonies were counted. 15 strains could still form colonies after heat treatment, of which 8 strains had a spore germination rate of >60% at pH 3.0.

[0019] 3. Quantitative evaluation of acid tolerance performance LB liquid medium with different pH (2.0, 2.5, 3.0, 3.5, 4.0, 5.0) was prepared. 8 candidate strains were inoculated and cultured at 14°C for 48 h, and the growth curve, spore formation rate, and acid tolerance index (ATI) were determined. The results of acid tolerance performance determination of some strains are shown in Table 1.

[0020] Table 1: Results of acid tolerance performance determination of some strains

[0021] As can be seen from Table 1, the QD-QJ-062 strain showed the best performance, with an ATI of 0.68 at pH 2.5 and a spore formation rate of 72%. This strain can still survive at pH 2.5 (ATI >0.3), and is suitable for further study.

[0022] 4. Molecular biology identification The QD-QJ-062 strain was gram-positive, rod-shaped, produced oval spores, and formed circular white opaque colonies on LB solid medium. The optimal growth pH was 4.0-5.5, and the pH tolerance range was 2.5-7.0. The 16S rRNA gene sequence was used for homologous sequence alignment in BLAST in NCBI, which had a similarity of 99.2% with Brevibacillus brevis, and was named Brevibacillus QD-QJ-062 strain, which was preserved in the China General Microbiological Culture Collection Center on March 14, 2025, with the preservation number of CGMCC No. 33725.

[0023] Example 2: Wastewater treatment effect of QD-QJ-062 strain The acid-containing iron wastewater (containing 6% H2SO4, Fe 2+The treatment process of 9970 mg / L, pH 3) was optimized, focusing on the intensification of Bacillus subtilis QD-QJ-062 strain on the removal of iron. The control group (conventional oxalate precipitation + chelating resin treatment) and the experimental group (oxalate precipitation + Bacillus subtilis intensification + chelating resin treatment) were compared and studied. The treatment process is shown in Figure 1 .

[0024] During the experiment, the control group used 100 mL of waste liquid directly added 6 g of oxalic acid to generate ferrous oxalate precipitate ( Figure 2 ), and then LG-701 chelating resin was used for treatment (adsorption flow rate 4 BV / h) after suction filtration. The experimental group added Bacillus subtilis QD-QJ-062 strain (inoculation amount 10 6 CFU / mL) under the same conditions, and the subsequent treatment was carried out after 2 hours of reaction. The experimental results showed that the Fe 2+ concentration of the control group could be reduced to 20 mg / L (removal rate 99.80%), while the experimental group with Bacillus subtilis QD-QJ-062 strain showed better treatment effect, and the Fe 2+ concentration was further reduced to below 2.0 mg / L (removal rate > 99.98%), meeting the requirements of resource utilization.

[0025] The intensification of Bacillus subtilis may be achieved through multiple mechanisms: first, the functional groups on the surface of the bacteria can adsorb iron ions; in addition, the strain may also fix iron ions through biomineralization. It is worth noting that after adding Bacillus subtilis, the utilization rate of oxalic acid in the system is improved, reducing the crystallization of oxalic acid and reducing the cost of reagent addition. At the same time, the introduction of Bacillus subtilis reduces the treatment load of the subsequent chelating resin, which helps to prolong the service life of the resin.

[0026] Based on the above experimental results, the optimized treatment process is as follows: wastewater is first treated by oxalate precipitation (assisted by Bacillus subtilis intensification) → thickening tank concentration → sedimentation tank separation → pressure filter solid-liquid separation → chelating resin deep treatment → limestone neutralization to pH 6~8 for water reuse, and the generated high-purity calcium sulfate as byproduct. Ferrous oxalate produced by precipitation as chemical byproduct. This process not only improves the removal efficiency of iron ions, but also realizes the recycling of resources, with good economic and environmental benefits.

Claims

1. A wastewater treatment bacterium, characterized in that, The wastewater treatment bacteria mentioned are Bacillus, with the preservation number CGMCC No. 33725.

2. The application of the wastewater treatment bacteria according to claim 1 in the treatment of acidic wastewater.

3. The application as described in claim 2, characterized in that, The acidic wastewater mentioned is an acidic wastewater containing iron ions generated during the production of titanium dioxide.

4. A method for treating iron-containing waste sulfuric acid wastewater from titanium dioxide production, characterized in that, The method described herein utilizes the wastewater treatment bacteria as described in claim 1 for treatment.

5. The method as described in claim 4, characterized in that, The method includes the following steps: 1) Add the wastewater to be treated to the reaction tank, and then add oxalic acid and the wastewater treatment bacteria described in claim 1 to react and generate a treatment solution containing ferrous oxalate precipitate; 2) The treated liquid from 1) is introduced into a thickening tank for concentration to obtain concentrated liquid and clarified liquid; 3) The concentrate enters the primary sedimentation tank and the secondary sedimentation tank. The ferrous oxalate precipitate obtained from sedimentation is added to the filter press for solid-liquid separation to obtain a high-purity ferrous oxalate byproduct. The filter water is combined with the clarified liquid obtained in 2). 4) The combined wastewater is adsorbed using chelating resin LG-701 to further remove iron ions from the wastewater and obtain a high-purity sulfuric acid solution. 5) Add limestone slurry to sulfuric acid solution to produce pure calcium sulfate byproduct. The pH of the wastewater reaches the range of 6-8 and can be reused.

6. The method as described in claim 5, characterized in that, The inoculation amount of the wastewater treatment strain in claim 1 of the method is 10. 6 CFU / mL.

7. The method as described in claim 5, characterized in that, In the method described, the oxalic acid added is 6% by mass and volume.

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