中国有色冶金

Non-ferrous metal hydrometallurgical wastewater contains a large amount of organic matter, sulfate, sodium chloride and other salts. Frozen denitrification technology uses the principle of solid-liquid equilibrium to achieve freezing separation, which can precipitate low-solubility solutes under low temperature conditions to obtain high-purity salt crystallization and concentrated wastewater, but the remaining concentrated wastewater still contains high concentrations of Na₂SO₄ NaCl and COD. Still can’t discharge outside. In this paper, freezing denitrification-evaporation concentration technology is used to treat COD high-salt wastewater containing Na₂SO₄ and NaCl, and the effects of freezing denitrification temperature and initial concentration of NaCl on the product are analyzed. Concluded as follow: In the freezing temperature range of 0~10℃, the residual COD in frozen crystal is less than 30%, and the best freezing temperature is 8℃; The higher the ratio of Na₂SO₄ NaCl mass content, the higher the purity of the precipitated Na₂SO₄ crystals; Taking advantage of the difference in the concentration ratio and solubility of the substances in the sodium chloride-sodium sulfate-water three-phase system, the separation of sodium sulfate and sodium chloride is effectively realized. The experimental products are Glauber’s salt, Na₂SO₄ crystals and hetero salt products. Using this technology to treat Na₂SO₄ and crude salt industrial products can realize the resource utilization of COD-containing high-salt wastewater, and realize zero pollution discharge.