Crystallization of Calcium Sulfate for Mining Wastewater Treatment

Abstract

This study aims to increase the particle size of the precipitate, aiming for an increasing settling speed. The effluent contains 21.88 g/L of sulfate, 526.5 mg/L of calcium, 2.9 mg/L of cadmium, 4.73 g/L of magnesium, 332.8 mg/L of manganese, and 205.8 mg/L of zinc. Based on thermodynamic simulations, evaluating the pH increase up to 9.0, it was possible to determine that the main species are CaSO4·2H2O(s), Mg(OH)2(s), MnO2(s), ZnO(s), and Cd(OH)2(s). In the precipitation tests, it was determined that a concentration of 2.0 mol/L of Ca(OH)2 resulted in a particle size of 12.2 µm. The increase of temperature has an opposite effect, decreasing 40% of the particle size at 80 °C in comparison to 25 °C. On the other hand, the reaction time increases particle size, reaching 300% of an increase from 10 min to 3 h. In the seed tests, it was found that a seed ratio of 10 g/L to 100 g/L with the CaSO4 (2) seed had the greatest impact on particle size growth, resulting in a 700% increase in particle size compared to the test without seeds. In the settling tests, a sedimentation rate of 177 mL/min was achieved using seeds and flocculants, compared to 50 mL/min in the test without reagents.