The main factors affecting the recovery of sodium cyanide by sulfuric acid process are:
1. The amount of sulfuric acid is acidified and deoxidized, and the alkaline cyanide-containing wastewater must be converted to acidic conditions. In addition to neutralizing the protective alkali, the amount of acid required for the analysis of free cyanide and complex should be satisfied. Acidity is an important factor. By controlling the acid amount in the range of 0.2 to 0.3% (or pH=2.5), it is possible to control the appropriate acid consumption and obtain a good purification index.
2. Blowing off the air volume The blown air volume should be sufficient to separate the resolved HCN gas from the liquid and carry it away with the air flow. The amount of production stroke is related to the nature of the cyanide plant wastewater, process flow, equipment performance and other conditions, and should be determined by experiments.
3. Sewage spray intensity in the alkali absorption tower The spray strength refers to the amount of sewage treated by the absorption tower per unit cross section. The spray intensity is large, the liquid is poorly dispersed in the tower, the de-cyanide ratio of the sewage is poor compared with the recovery rate of sodium cyanide, and the spray strength is small, the dispersion degree is high, and the purification effect is good.
4. When the temperature of the sewage increases in the tower, the formation and dissociation speed of HCN will increase rapidly. Of course, whether to increase the temperature, this should consider the economic effects and treatment effects. In production, the temperature is generally controlled at 25 to 30 ° C.
5. Thiocyanate In the sewage treatment process, the non-toxic thiocyanate cannot be decomposed by acid, and the monovalent copper ion in the solution forms stable copper cyanide [Cu 2 (CNS) 2 ] precipitate. Therefore, before the treatment of sewage, the content of copper and thiocyanate should be accurately determined to ensure that the content of thiocyanate is slightly larger than the content of copper, so as to avoid the high content of cyanide and copper in the treated waste liquid. Cyanide loss.
6. The concentration of the lye increases the concentration of the lye, which is beneficial to the absorption of hydrogen cyanide in the absorption tower; on the contrary, the hydrogen cyanide gas in the gas stream cannot be completely absorbed, and is brought into the tower to affect the blowing effect. . In practice, the concentration of the lye initially prepared is about 15%, and it is suitable to be 1 to 1.5% at the end of the absorption.
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