Influence of Low-Grade Solid Potash Mineral Composition on Potassium Extraction and Lithium Distribution During Solution Mining in Mahai Salt Lake, Qaidam Basin

Abstract

As high-grade potash resources become increasingly scarce and lithium is recognised as a valuable co-product, the low-grade solid potash deposits in the Mahai Salt Lake, Qaidam Basin, have become increasingly significant targets for potash resource development. However, the inefficient release of potassium from these low-grade ores constrains their economic feasibility for industrial use. This study addresses this challenge by employing x-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and observational borehole monitoring data to systematically analyse the mineralogical characteristics of these ores and their influence on potassium ion release during solid–liquid conversion. The results identify carnallite, sylvite, and polyhalite as the primary potash minerals, with a significant spatial variations across the study area that directly impact potassium ion release and migration. Sylvite and carnallite in shallow strata are more reactive with solvents, facilitating rapid potassium ion release, whereas polyhalite, hosted within the intercrystalline clastic materials of halite, demonstrates limited pore connectivity, resulting in a slower release rate. Monitoring borehole data indicate that variations in solvent injection volumes cause significant fluctuations in water levels and potassium ion concentrations, thereby affecting potash dissolution rates. As solution mining progresses, high-lithium areas gradually expand, with lithium concentrations in brine reaching up to 120.4 mg/L and generally ranging from 20 to 70 mg/L. The spatial correlation between potassium and lithium distribution suggests that lithium can be effectively recovered as a co-product. Adjustments in solvent injection rates and concentrations, based on mineral distribution and monitoring data, are essential for optimising the dissolution efficiency of both potassium and lithium during production.