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

Abstract

The application provides a method for treating and recycling iron-containing waste sulfuric acid in titanium dioxide production, which is based on screening of a strain capable of treating iron-containing waste water in a low pH environment, and establishes a method for treating iron-containing waste sulfuric acid, which can effectively realize resource recycling. The waste water treatment bacteria used are Bacillus QD-QJ-062 strain, and the preservation number is CGMCC No.33725. The QD-QJ-062 strain of Bacillus screened by the application can effectively treat the iron-containing waste water in a low pH environment, promote the generation of ferrous oxalate precipitation, and generate ferrous oxalate by-products. The generated ferrous oxalate can be converted into ferrous sulfate by sulfuric acid, and oxalic acid can be recycled, thereby reducing the operation cost. The sulfuric acid solution after iron removal can be neutralized by limestone to generate high-purity gypsum, thereby realizing resource recycling and treatment.

Description

Technical Field

[0001] This invention belongs to the field of environmental pollution control and resource utilization, specifically relating to a method for the treatment and resource utilization of iron-containing waste sulfuric acid generated during the production of titanium dioxide. Background Technology

[0002] Titanium dioxide is a commonly used white pigment, widely applied in coatings, plastics, papermaking, printing, and other fields. my country has become the world's largest producer of titanium dioxide. The production process of titanium dioxide is mainly based on the sulfuric acid process, using titanium concentrate, high-titanium slag, or titanium-rich materials as the main raw materials. The industrial process of producing titanium dioxide using sulfuric acid is called the sulfuric acid process. The wastewater generated in the production process is characterized by large volume, high acidity, high suspended solids, and high ferrous iron content. The "National Hazardous Waste List" (2025 edition) HW34 Waste Acid 264-013-34 stipulates that "waste acid generated during the sulfuric acid process for producing titanium dioxide (titanium dioxide) is hazardous waste, with hazardous characteristics of C and T." If the wastewater from titanium dioxide production is not effectively treated, it will cause serious damage to the ecological environment and also result in the waste of sulfuric acid.

[0003] The sulfuric acid process for producing titanium dioxide mainly includes acidolysis, hydrolysis, washing, and bleaching. Wastewater primarily comes from water or sulfuric acid added during these processes and mainly contains H₂. + and SO4 2- Accompanied by Fe 2+ Ti 3+ Cr 2+ Mg 2+ wait.

[0004] Currently, conventional treatment processes typically involve neutralizing the waste acid with lime or carbide, followed by aeration and sedimentation to separate the mud and water. The slurry is then filtered to produce gypsum, and the filtrate undergoes further treatment before being discharged in compliance with standards. Neutralization treatment offers advantages such as low investment and simple operation, but impurities like metal ions from the waste sulfuric acid remain in the byproducts, easily causing secondary pollution and hindering the reuse of the byproducts. Meanwhile, gypsum and other byproducts are still primarily used in the physical production of low-end building materials. Due to market capacity and product sales radius limitations, it is difficult to dispose of the large quantities of gypsum generated during neutralization on a large scale. The main method is to construct stockpiles for gypsum storage, which involves high investment, land occupation, waste of sulfur and calcium resources, and impacts public safety. Currently, due to significant environmental pressure, no new stockpiles are being approved. Industrial byproduct gypsum is washed away by rainwater, and soluble harmful substances dissolve in water, severely polluting surface and groundwater through system circulation. Simultaneously, gypsum is dispersed into the atmosphere as powder by wind and sun and settles on surfaces, polluting the environment and threatening 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:

[0012] 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;

[0013] 2) The treated liquid from 1) is introduced into a thickening tank for concentration to obtain concentrated liquid and clarified liquid;

[0014] 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).

[0015] 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.

[0016] 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.

[0017] Furthermore, in the method described, the inoculum quantity of Bacillus QD-QJ-062 strain is 10. 6 CFU / mL; oxalic acid added was 6% by mass and volume.

[0018] This invention utilizes the screened Bacillus strain QD-QJ-062, which can effectively treat iron-containing wastewater under low pH conditions, promoting the precipitation of ferrous oxalate and generating ferrous oxalate as a byproduct. Sulfuric acid can also be used to convert the generated ferrous oxalate into ferrous sulfate, recovering oxalic acid and reducing operating costs. The sulfuric acid solution after iron removal can be neutralized with limestone to generate high-purity gypsum (CaSO4), achieving resource recovery and treatment. Attached Figure Description

[0019] Figure 1 Flow chart of acidic iron-containing wastewater treatment process: ①: discharge port ②: reaction conveyor belt ③: reaction tank ④: control valve ⑤: storage tank ⑥: conical flask ⑦: circulating water vacuum pump;

[0020] Figure 2 Diagram of acidic wastewater treatment process: A is the water sample before treatment of iron-containing acidic wastewater, and B is the precipitate formed after adding oxalic acid and Bacillus strain QD-QJ-062. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0022] Example 1: Screening of acid-resistant strains

[0023] 1. Initial screening of strains

[0024] Wastewater and bottom sludge samples (pH 3.5–4.0) were collected from a sewage discharge channel in Qingdao Chengyang Industrial Park in March 2024. This discharge channel has long received acidic wastewater (containing sulfuric acid) from a nearby stainless steel foundry. After filtration through filter paper, the samples were subjected to 10–100 ml of phosphate buffer solution (pH 4.0). 4 Diluted multiple times.

[0025] Culture medium formulation (pH 3.5): 10g peptone, 5g yeast extract, 10g NaCl, 15g agar, citrate-disodium hydrogen phosphate buffer (pH 3.5), and distilled water to a final volume of 1L. 100 µL of each serially diluted solution was spread onto acidic LB agar plates. Incubation was carried out at 14℃ for 96 h. Colony morphology was observed, and single colonies were selected for acid tolerance testing at pH 2.5–4.0. A total of 45 strains were isolated that could grow at pH 3.5. Among them, 23 strains could still grow at pH 3.0 (OD 600 > 0.3).

[0026] 2. Screening for spore formation ability

[0027] Spore induction medium (pH 4.0): 8g nutrient broth, 0.01g MnSO4·H2O, 0.1g CaCl2, citrate buffer (pH 4.0), 1L distilled water. Twenty-three acid-resistant bacterial strains were inoculated into the spore induction medium and cultured at 180 rpm and 30℃ for 48 h with shaking. 1 mL of the bacterial suspension was incubated at 80℃ for 10 min and spread onto LB agar plates at pH 4.0. The plates were then incubated at 25℃ for 48 h, and surviving colonies were counted. Fifteen strains were still able to form colonies after heat treatment, and eight of these strains showed a spore germination rate >60% at pH 3.0.

[0028] 3. Quantitative evaluation of acid resistance

[0029] LB liquid medium with different pH values ​​(2.0, 2.5, 3.0, 3.5, 4.0, 5.0) was prepared. Eight candidate strains were inoculated and cultured at 14℃ for 48 h. Growth curves, spore formation rate, and acid tolerance index (ATI) were measured. The results of acid tolerance tests for some strains are shown in Table 1.

[0030] Table 1. Results of acid resistance testing for some strains

[0031]

[0032] As shown in Table 1, strain QD-QJ-062 exhibited the best performance, with an ATI of 0.68 and a spore formation rate of 72% at pH 2.5. This strain can still survive at pH 2.5 (ATI>0.3), making it suitable for further research.

[0033] 4. Molecular biological identification

[0034] The QD-QJ-062 strain is Gram-positive, rod-shaped, and produces oval spores. On LB agar, it forms round, white, opaque colonies. Its optimal growth pH is 4.0–5.5, and it tolerates a pH range of 2.5–7.0. The 16S rRNA gene sequence was sequenced and compared with BLAST in NCBI, showing a 99.2% similarity to *Brevibacillus brevis*. It was named *Bacillus brevis* strain QD-QJ-062 and deposited on March 14, 2025, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 33725.

[0035] Example 2: Wastewater treatment effect of strain QD-QJ-062

[0036] For acidic iron-containing wastewater (containing 6% H2SO4, Fe) 2+ The treatment process (concentration 9970 mg / L, pH 3) was optimized, with a focus on investigating the enhancing effect of Bacillus brevis strain QD-QJ-062 on iron removal. A control group (conventional oxalic acid precipitation + chelating resin treatment) and an experimental group (oxalic acid precipitation + Bacillus brevis enhancement + chelating resin treatment) were set up for comparative study. The treatment process is detailed below. Figure 1 .

[0037] During the experiment, the control group used 100 mL of waste liquid to directly add 6 g of oxalic acid to generate ferrous oxalate precipitate. Figure 2 After filtration, the samples were treated with LG-701 chelating resin (adsorption flow rate 4 BV / h). The experimental group was treated under the same conditions with the addition of Bacillus strain QD-QJ-062 (inoculum size 10). 6 (CFU / mL), reacted for 2 hours before further treatment. Experimental results showed that the final effluent from the control group contained Fe... 2+ The concentration could be reduced to 20 mg / L (removal rate 99.80%), while the experimental group with added Bacillus strain QD-QJ-062 showed even better treatment effect, with effluent Fe... 2+ The concentration was further reduced to below 2.0 mg / L (removal rate >99.98%), meeting the requirements for resource utilization.

[0038] The enhancing effect of Bacillus may be achieved through multiple mechanisms: firstly, the functional groups on the bacterial surface can adsorb iron ions; secondly, the strain may also fix iron ions through biomineralization. Notably, the addition of Bacillus improves the system's utilization of oxalic acid, reduces oxalic acid crystallization, and lowers reagent dosage costs. Simultaneously, the introduction of Bacillus reduces the processing load on subsequent chelating resins, helping to extend the resin's lifespan.

[0039] Based on the above experimental results, the optimized treatment process is as follows: wastewater first undergoes oxalic acid precipitation (with Bacillus subtilis enhancement) → thickening in a thickener → separation in a sedimentation tank → solid-liquid separation in a filter press → deep treatment with chelating resin → neutralization to pH 6-8 with limestone before water reuse, with the generated high-purity calcium sulfate as a byproduct. Ferrous oxalate produced by precipitation is treated as a chemical byproduct. This process not only improves the removal efficiency of iron ions but also achieves resource recovery and utilization, resulting in good economic and environmental benefits.

Claims

1. A wastewater treatment bacterium, characterized in that, The wastewater treatment bacteria mentioned are Bacillus (Bacillus) Bacillus sp .) Strain QD-QJ-062, 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, characterized in that, The acidic wastewater mentioned is an acidic wastewater containing iron ions generated during the production of titanium dioxide.

3. 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.

4. The method as described in claim 3, 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.

5. The method as described in claim 4, characterized in that, The inoculation amount of the wastewater treatment strain in claim 1 of the method is 10. 6 CFU / mL.

6. The method as described in claim 4, characterized in that, In the method described, the oxalic acid added is 6% by mass and volume.

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