Phosphorus Release from Oxidized Phosphate Rocks under Variable TDS Water Conditions

This study examines the effect of water with varying total dissolved solids (TDS) on the phosphorus dissolution behavior of oxidized phosphate rock (PR) samples, specifically high-grade (MHPR) and medium-grade (MMPR) micro-sized fractions, under non-acidic conditions. Comprehensive characterization revealed distinct chemical, mineralogical, and petrographic differences between the samples. MMPR contained a higher abundance of evaporite minerals, particularly gypsum and anhydrite, contributing to its elevated SO₃ content. In contrast, MHPR was enriched in SiO₂ due to the presence of detrital quartz. The higher pH values observed in MMPR leachates were attributed to their greater carbonate content, especially ankerite, which increases solution alkalinity. Leaching experiments showed that as the TDS of the input water increased, the TDS of the resulting leachates also rose proportionally. However, phosphorus (P) dissolution decreased at higher TDS levels, likely due to elevated alkalinity inhibiting P solubility. MHPR consistently released more phosphorus than MMPR, a trend associated with its lower carbonate content and more favorable dissolution environment.