Purification of foul water from the production of silicon carbide

Abstract

666.762.853~0i3,8:628.543~069 Silicon carbide products are used in various branches of industry and are in ever increas~ ing demand. However, output is held back by the lack of the necessary amount of the original material, silicon carbide. In this connection it is planned to construct at one of the refractory plants a shop for the production of silicon carbide in order to satisfy the growing demands from industry, but the production of silicon carbide however is accompanied by the formation of significant quantities of contaminated effluent.In order to develop the technical solutions for the protection of the natural water reservoirs from contamination, the composition, clarification and dewatering of the slurry from the foul water from abrasive plants which produce black and green SiC and operate a virtually identical technology have been studied.The composition of the contaminated foul water in question is given in Table i. The foul water forming during the production of SiC and in the production of SiC powders of various grades of coarseness are not uniform in the type of contamination.The foul water from the washing of fused green SiC is contaminated by up to 1 g/liter of suspended matter and by up to 3 g/liter (27 kg/ton) of sodium chloride due to the addition of common salt to the batch. In addition, there is also an increase in the concentration of sulfate ions, witha specific increase of ~2 kg/ton of melted lumps of SiC. When the black SiC is washed, the foul water is contaminated mainly by suspended matter.During milling, classification, and wet purification of the aspirated air and the removal of particles, the foul water is mainly contaminated by suspended matter (from 2 to 5 g/liter), and leaching of dissolved salts from the solid phase is quite insignificant.In the chemical beneficiation, the powdered SiC is treated with sulfuric acid to remove the hammered-on iron (30-90 kg/ton) and this is followed by the neutralization of the liquid phase by sodium hydroxide. This form of foul water is the most contaminated both by the dissolved mineral salts and acid (up to 70 g/liter) and also by iron hydroxide (9-36 g/liter) which is in a suspended state.