Wastewater Treatment Technology for Titanium Dioxide Production by Sulfuric Acid Process

Sulfate-reducing bacteria (sRB) method, as a potential technology to control sulfate pollution, has gradually become a research hotspot of scholars. High-concentration sulfate wastewater can easily cause the pH value of the water body to decrease, the soil becomes acidic, and the concentration of heavy metals increases, which seriously affects the surrounding ecological environment. Study the influencing factors of sulfate ion removal in sulfate wastewater: temperature, pH, C/S, trace elements, etc., find the best conditions and parameters for desulfurization of sulfate-containing wastewater, and study the improvement of the reactor in the biological desulfurization process of sulfate wastewater.

Production process of titanium dioxide by sulfuric acid method

The crushed ilmenite (main component FeTiO3) enters the acid hydrolysis tank. Under the action of sulfuric acid, most of the mineral powder is decomposed to form a soluble sulfate mixed solution. After the acid hydrolysis is completed, it enters the settling tank. A certain amount of precipitation agent is added to the sedimentation tank, so that the suspended solids in the solution and substances that are easy to form colloids such as Al and Si are settled and separated. The supernatant liquid enters the crystallization process for cooling and crystallization, and the lower turbid liquid enters the disc filter for solid-liquid separation. . The cooled supernatant liquid obtains a two-phase mixture of FeSO4·7H2O crystals and titanium liquid, and then a pure high-concentration titanium liquid can be obtained through filtration and concentration processes. The high-concentration titanium solution is heated and hydrolyzed in an acidic environment, and after a process of hanging film, washing, bleaching, secondary hanging film, and secondary water washing, a high-concentration metatitanic acid (chemical formula is TiO2·H2O) slurry is finally obtained. Finally, it enters the rotary furnace for calcination and then goes to the grinder to pulverize and package to obtain high-purity titanium dioxide.

Source of wastewater and water quality analysis

Source of wastewater: It can be clearly seen from the above process flow chart of titanium dioxide production by sulfuric acid method that the waste acid and acid wastewater of the whole plant system mainly come from the washing process, and the source of these wastewater is acid hydrolysis, hydrolysis, washing and bleaching, etc. Water or sulfuric acid added in the process. In order to clean the metal ions and soluble matter attached to the metatitanic acid slurry, it is necessary to add a large amount of water to wash the slurry, and the ion concentration in the washing water can only enter the next process after the ion concentration reaches the relevant technological standard. As a result, the washing process requires a particularly large amount of washing water. Specifically, for a titanium dioxide factory with an annual output of 10,000 tons/year, the daily washing wastewater volume is as high as 5,000m3.

Water quality analysis The wastewater produced by the sulfuric acid method titanium dioxide production process mainly contains a large amount of H+ and SO42- and metal ions such as Fe2+, Ti3+, Cr2+, Mg2+ brought into the mineral powder, and the mother liquor after hydrolysis contains a large amount of mass concentration of about 22 % of dilute sulfuric acid, a small amount of FeSO4 and TiOSO4, etc. The primary and secondary washing wastewater comes from the sulfuric acid and other ions attached to the metatitanic acid slurry and the sulfuric acid added during the bleaching process. The main components are sulfuric acid with a concentration of 0.5-3% and FeSO4. Due to the presence of a large amount of H+ in the wastewater, the wastewater is usually acidic, the pH value is about 1-3, and the chromaticity value is high, causing serious environmental pollution.

① Treatment of the waste acid of the hydrolysis mother liquor The waste acid in the hydrolysis mother liquor contains a large amount of dilute sulfuric acid, which can be neutralized with slaked lime and the by-product calcium sulfate is recovered. After filtering and washing, the hydration of calcium sulfate can be obtained. material (commonly known as gypsum), which can be used in the construction industry;

② Treatment of mixed acid wastewater The main method of treating wastewater in sulfuric acid method titanium dioxide factory is “neutralization + aeration”. Acid wastewater from the first washing, second washing and hydrolysis of the system first passes through the inclined plate sedimentation tank for natural sedimentation , the supernatant overflows to the buffer tank, and at the same time, the acid hydrolysis tail gas spray wastewater and the ground flushing water also enter the buffer tank together. After the above acidic waste liquid enters the buffer tank of the pollution control workshop, it is adjusted for acidity, and then sent to the primary neutralization barrel of the pollution control workshop with an acid-resistant pump, and the pH value is adjusted to 3.5-4.5 with limestone slurry, and then enters the secondary neutralization barrel. Adjust pH to 7-9 with carbide slag and lime slurry. After the pH value adjustment in the neutralization barrel is qualified, it is pumped to the primary plate and frame filter press in the pollution control workshop for solid-liquid separation. The separated solid (titanium gypsum) is transported to the yard by truck, and the liquid enters the aeration tank. , and aerated it with compressed air to reduce the COD content in the wastewater.

Advanced ASBR method to treat sulfate wastewater

In the influent period, the wastewater enters the reactor, and the volume of the influent is determined by the following factors, HRT, organic load, and sludge settling characteristics.

The reaction stage requires stirring, generally in a batch mode, and this stage is an important stage in the conversion of organic matter. Stop stirring during the settling period to make it an ideal settling state. The settling time is generally 10-30 minutes, which should not be too long, otherwise the granular sludge will be re-suspended due to the continuous production of biogas. After that, the total amount of effluent is equal to the amount of influent. After the drainage is completed, the reactor enters the next cycle.

Since the sludge with poor sedimentation performance can be discharged together when the water is discharged, the overall sedimentation performance of the sludge in the system is good. At the same time, the granulation process is shorter, which improves the ability to treat wastewater. Because the ASBR process can effectively prolong the residence time of sludge and ensure sufficient mixing of mud and water, it has good adaptability to temperature. In addition to treating wastewater at room temperature and high temperature, it can also effectively treat high and low concentration wastewater at low temperature. Therefore, There are good application prospects.

Conclusion

The production of titanium dioxide in my country mainly adopts the sulfuric acid method. The use of this process is bound to generate a large amount of waste water and cause huge pollution to the environment. It does not conform to the concept and strategic policy of sustainable development in my country. Therefore, the wastewater produced by the sulfuric acid method must be properly treated to reduce its harm to the environment. However, my country is not very mature in this regard, and it is necessary to further strengthen the investment in wastewater treatment technology. I have done some simple research that I hope will help.

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