China is a big 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 the production process of sulfuric acid method, in order to wash ferrous ions, a variety of waste acid wastewater will be generated, mainly including waste acid from the first wash (25% sulfuric acid), water from the second wash (5% sulfuric acid), and wastewater from the third wash.
The waste acid of the first wash and the second wash water are neutralized with quicklime to produce a large amount of titanium gypsum industrial sludge, the main component of which is CaSO4﹒2H2O, which is usually 70 to 80% acidic or neutral. Because it contains a large amount of iron, its color is reddish brown. It is also called red gypsum or yellow gypsum. Due to the high iron content, the strength of calcined into hemihydrate gypsum is low, or even weak, and cannot be used in the construction field. As a result, the comprehensive utilization rate of titanium gypsum is very low. At present, most of the titanium dioxide enterprises adopt stacking or landfilling methods for disposal. The cost of the construction of the site and environment, if not handled properly, 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 of water resources.
Application introduction: Aiming at the bottleneck that the existing technology cannot be implemented, Jiangsu Jiuwu High-tech Co., Ltd. relies on mature and complete membrane integration process technology, and uses inorganic ceramic membrane as the main membrane process to treat waste acid wastewater. It mainly recovers metatitanic acid or titanium dioxide, reuse of reclaimed water and wastewater, and purification of waste acid to make gypsum. 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. The second wash water of sulfuric acid method (low acid wastewater): the second wash water (low acid wastewater, containing 5% acid, 5000ppm of ferrous iron). Metatitanic acid is recovered by inorganic membrane, ferrous ion is removed by acid-resistant nanofiltration membrane after heat exchange of produced water, and the permeate of nanofiltration is neutralized with lime to obtain dihydrate gypsum. Alpha or beta architectural gypsum is produced through the unique crystal conversion process of Jiangsu Jiuwu High-tech, and the neutralized water can be reused by more than 60% through the membrane integrated device.
2. Sulfuric acid method three-wash water (treatment water after chlorination method): the third-wash water is wastewater after coating (titanium dioxide: 200-500ppm, conductivity: 6000-10000μs/cm). Inorganic ceramic membrane is used to recover titanium dioxide, and the produced water is concentrated by reverse osmosis membrane after heat exchange. The recovery rate is over 90%. The concentrated solution is separated into salt by nanofiltration membrane to separate sodium sulfate and sodium chloride. Sodium chloride can be used as a raw material for chlor-alkali, and sodium sulfate can be used as calcium chloride to neutralize water. A large amount of calcium chloride is produced after neutralization).
1. The turbidity of the product water is stable below 0.5NTU, the conductivity is ≤10μs/cm, and the water quality is stable.
2. Compared with the traditional technology, a titanium dioxide enterprise with a budget of 100,000 tons can recover more than 5 million yuan of titanium dioxide every year by adopting the membrane process, and save more than 2 million yuan 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 and unattended.