Recovery of magnesium and potassium from biotite by sulfuric acid leaching and alkali precipitation with ammonia

A process for the recovery of magnesium (Mg) and potassium (K) from biotite was developed using sulfuric acid leaching and precipitation with ammonia. The optimum conditions for dissolution of biotite were found to be sulfuric acid solution of 2.5 mol/L, sulfuric acid/biotite ratio of 4 mL/g, leaching temperature of 90 °C and leaching time of 2 h. Under these conditions, the leaching efficiency of Mg and K was found to be 95.8% and 94.9% respectively. By using the solubility differences of corresponding elements, a two-step precipitation process was applied to remove Fe and Al and recovery of Mg. Subsequently, magnesium hydroxide was prepared by precipitation from the leach solution with ammonia as the precipitant. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses showed that the high purity Mg(OH)2 existed in the form of flower-like spherical aggregation. Furthermore, the final solution of ammonium-potassium sulfate can be used for agricultural compound fertilizer.