Preparation of sodium sulfate by isohydric crystallization during reverse osmotic treatment of mineralized wastewater and solution neutralization
The article is devoted to the problem of neutralization of industrial wastewater containing highly toxic chlorides, sulfates, nitrates, ions of heavy and non-ferrous metals. Wastewater, as a rule, has an acidic reaction, and the first stage of its neutralization consists in the use of alkaline reagents (NaOH, Na2CO3, Ca(OH)2) to neutralize and form hybrid sediments of iron, aluminum and other metals. The total concentration of salt components in technological solutions ranges from 10 to 100 g/L, most often it is a mixture of Na2SO4, NaCl, NaNO3, less often other salts. The technology of deep processing of mineralized water consists in softening, filtration on pressure filters and microfiltration of industrial waste. The peculiarity of the proposed scheme lies in the use of the reverse osmosis method of desalting, according to which it is concentrated by 3-5 times and evaporated to a salt content of 200-300 g/L. This scheme allows you to obtain concentrate and fresh water that meets environmental requirements. After water demineralization, the concentrate goes to isohydric crystallization with Na2SO4 · 10H2O by cooling to 0 оС. After centrifugation of the pulp, the mother liquor is mixed with the initial stream and sent to a reverse osmosis unit, and the crystalline hydrate is sent to drying to obtain anhydrous technical salt. On the example of a model technological solution that simulates liquid industrial waste from mining enterprises, with the help of computational and experimental studies, the fundamental possibility of obtaining anhydrous sodium sulfate by means of intracycle isohydric crystallization of a concentrate after a reverse osmosis plant has been shown. A schematic diagram of the neutralization of liquid inorganic waste of I and II hazard classes with the production of a secondary product, Na2SO4, is proposed; the possibility of isomorphic capture of impurities during its crystallization is estimated.