Nitric acid pressure leaching of limonitic laterite ores: Regeneration of HNO3and simultaneous synthesis of fibrous CaSO4•2H2O by-products

An innovative technology, nitric acid pressure leaching of limonitic laterite ores, was proposed by our research team. The HNO3 regeneration is considerable significance for the improvement of the proposed technology and its commercial application, but it has not been systematically investigated. Herein, regenerating HNO3 from Ca(NO3)(2) solution with low-cost H2SO4, and simultaneous synthesis of fibrous CaSO4 center dot 2H(2)O by-products were studied. As a theoretical basis, the solubility of CaSO4 center dot 2H(2)O in HNO3 medium is studied. It is concluded that the solubility of CaSO4 center dot 2H(2)O increases with increasing temperature or increasing HNO(3)concentration, which has considerable guiding significance for the subsequent experimental research and analysis. Then, the effects of various factors on the residual Ca2+ concentration of filtrate, the regenerated HNO3 concentration and the morphology of synthesized products are investigated using ICP-AES and SEM. And the effect mechanism is also analyzed. The results indicate the regenerated HNO(3)concentration reaches 116 g/L with the residual Ca2+ concentration being 9.7 g/L at the optimum conditions. Moreover, fibrous CaSO4 center dot 2H(2)O by-products with high aspect ratios (length, 406.32 mu m; diameter, 14.71 mu m; aspect ratio, 27.62) can be simultaneously synthesized.