China is a major producer of titanium dioxide, with an annual production of about 3 million tons of titanium dioxide, of which sulfuric acid method titanium dioxide accounts for 95% of the total output. In order to wash ferrous ions in the production process of the sulfuric acid method, a variety of waste acid wastewater is generated, mainly waste acid from the first wash (25% sulfuric acid), water from the second wash (5% sulfuric acid), and wastewater from the third wash.
A large amount of titanium gypsum industrial sludge is produced after the waste acid of the first wash and the second wash water are neutralized with quicklime. Its main component is CaSO4﹒2H2O, which is usually 70~80% in grade, acidic or neutral. This is because it contains a lot of iron. It is also called red gypsum or yellow gypsum. Due to the high iron content, the strength of calcined into hemihydrate gypsum is low. It cannot be used in the construction field, resulting in a low comprehensive utilization rate of titanium gypsum. At present, most of the titanium dioxide enterprises use stacking or landfilling methods for disposal. The accumulated amount of landfills over the years is nearly 100 million tons. In addition to occupying a large amount of land resources, they also have to pay high costs for the construction of the storage yard. If it is good, it will cause triple pollution of water, atmosphere and soil. The wastewater from the third wash contains a large amount of titanium dioxide, and direct discharge not only causes the economic loss of titanium dioxide, but also a large amount of waste.
Aiming at the bottleneck that the existing technology cannot be implemented, Jiangsu Jiuwu Hi-tech Co., LTD relies on mature and complete membrane integration process technology, responds to the national environmental pollution "source control" policy. It uses inorganic ceramic membrane as the main membrane process to treat acid waste water, mainly to recover metatitanic acid or titanium dioxide, reuse reclaimed water and wastewater, purify waste acid into gypsum, etc. It not only enables the reuse of titanium dioxide resources, the reuse of water resources, but also solves the problem of red gypsum stacking.
1. Sulfuric acid method second washing water (low acid wastewater): secondary washing water (low acid wastewater, containing 5% acid, ferrous 5000ppm). This uses inorganic membrane to recover metatitanic acid, and remove the product water by acid-resistant nanofiltration membrane after heat exchange Ferrous ions and nanofiltration permeate are neutralized by lime to obtain dihydrate gypsum. After Jiuwu's unique crystal conversion process, α or β building gypsum is produced, and the neutralized reclaimed water can be reused by 60% through the membrane integration device.
2. Sulfuric acid method three washing water (chlorination method post-treatment water): the third washing water is the wastewater after coating (titanium dioxide: 200-500ppm, conductivity: 6000-10000μs/cm). And the inorganic ceramic membrane is used to recover the titanium dioxide. The product water is concentrated by reverse osmosis membrane after heat exchange, and the recovery rate is over 90%. The concentrated liquid is salted through a nanofiltration membrane to separate sodium sulfate and sodium chloride. Sodium chloride can be used as raw material for chlor-alkali, and sodium sulfate can be used as raw material for chlor-alkali. Calcium chloride neutralizes the water (the chlorinated slag water is neutralized with gypsum in the production process of the chlorination process to produce a large amount of calcium chloride).
1. The turbidity of the product water is stably below 0.5NTU, the conductivity is ≤10μs/cm, and the water quality is stable.
2. Compared with the traditional technology, the titanium dioxide enterprise with a budget of 100,000 tons, using the ceramic membrane, can recycle more than one million US dollars of titanium dioxide every year and save more than 350,000 US dollars in water resources.
3. The problem of turning gypsum waste into treasure industry has also been solved, and the construction investment and project transformation are in line with the conditions of the existing technology. Traditional industrial disposal methods, such as storage in landfills, are used as cement additives.
4. Inorganic ceramic membrane has a service life of more than 5 years, and is not affected by acid, alkali, high temperature, high pressure, etc.
5. The ceramic membrane process is simple to operate, the technical process is short, and the control points are few. It can realize DCS automatic control unattended by people.