Concentrate the spent acid and return it to the acid for deacidification or for pickling steel or to supply calcium fertilizer

The immersion, combustion, evaporation and concentration of the spent acid are directly immersed in the waste acid by the high-temperature gas (about 1200 ° C) generated by the combustion of the fuel, so that the water in the spent acid is evaporated and the concentration is increased. Generally, a concentration of 55% sulfuric acid can be obtained by concentration. After the precipitate is removed, it can be used for pickling steel to remove rust, or with new concentrated sulfuric acid for acid hydrolysis. However, this acid contains high impurities and will have certain adverse effects on chemical fertilizers and pesticides.
After separation and crystallization, two stages of concentration were carried out. Can be obtained more than 75% sulfuric acid, less than 3.5% of residual salts, such acid containing less iron, calcium superphosphate fertilizer may be considered for preparation purposes. If this acid is used repeatedly for acid hydrolysis, the content of aluminum , iron, chromium , vanadium and other ions in the spent acid increases, which has an adverse effect. Although the improvement of aluminum has no effect on the whiteness of the product, it has an adverse effect on filtration. The increase in iron, chromium, and vanadium adversely affects the whiteness and optical properties of the product because chromium, vanadium, iron ions and titanic acid co-precipitate upon hydrolysis of the titanium liquid and are then introduced into the titanium dioxide lattice during calcination. However, it has been reported that the addition of sulfuric acid can remove trivalent cations and make the resulting precipitate easy to filter, and even eliminate the accumulation of chromatin in the spent acid. Some titanium dioxide plants will recover 75% sulfuric acid and concentrated sulfuric acid produced by ordinary contact method to 92% concentration, which is used to decompose ilmenite. As a result, the quality of the obtained titanium dioxide has not decreased, and no accumulation of impurities has been found.
It is also possible to first remove impurities such as iron ions in the spent acid with an ion exchange membrane, and then perform concentration by vacuum evaporation.
Dagang Titanium Company introduced dilute sulfuric acid treatment technology and equipment from Norma Company of Finland, and can recycle 26,000 tons of 80% sulfuric acid per year. The waste acid concentrating device is currently being developed and localized by the device. It is estimated that the domestic waste acid concentrating device can save 50%~60% of the investment compared with the introduction of foreign technology and equipment.

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