Hydrothermal Synthesis of Calcium Silicates on the Recovery of Phosphorus from Phosphorite

Calcium silicates with nanosized needle-like structure have been obtained from phosphorite by hydrothermal synthesis. Phosphorus is recovered from phosphorite as sodium phosphate solution under conditions of autoclave treatment of phosphorite with alkaline solution in the presence of silicon dioxide at 250°C. This approach enables involvement of low-phosphorus raw materials into non-waste processing owing to the synthesis of calcium silicates suitable in many branches of industry. Thus prepared phosphate solutions are applicable in agriculture and, after appropriate purification, in food industry. Hydrothermal synthesis conditions have been determined: temperature of 250–300°C, leaching time of 3 h, and NaOH concentration of 150 kg/m 3 .