Nitric acid pressure leaching of limonitic laterite ores: Regeneration of HNO₃ and simultaneous synthesis of fibrous CaSO₄·2H₂O by-products

Abstract

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 CaSO₄·2H₂O by-products were studied. As a theoretical basis, the solubility of CaSO₄·2H₂O in HNO₃ medium is studied. It is concluded that the solubility of CaSO₄·2H₂O increases with increasing temperature or increasing HNO₃ 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 HNO₃ concentration reaches 116 g/L with the residual Ca²⁺ concentration being 9.7 g/L at the optimum conditions. Moreover, fibrous CaSO₄·2H₂O by-products with high aspect ratios (length, 406.32 µm; diameter, 14.71 µm; aspect ratio, 27.62) can be simultaneously synthesized.

Keywords

limonitic laterite ores / Ca(NO₃)₂ solution / HNO₃ regeneration / CaSO₄·2H₂O by-products / solubility

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