Sequential determination of calcium chemical phases in gypsum-associated fluorite ores using ICP-OES

Abstract

Fluorite is a crucial non-metallic strategic mineral resource, commonly occurring in hydrothermal vein-type and sedimentary metamorphic fluorite deposits. Sedimentary metamorphic fluorite (CaF₂) frequently coexists with associated minerals, such as gypsum (CaSO₄·2H₂O) and calcite (CaCO₃). Accurately determining the contents of calcium sulphate, calcium carbonate, and calcium fluoride is essential for understanding mineralization mechanisms and for guiding the development of subsequent beneficiation and metallurgical processes. Existing analytical methods for fluorite are primarily developed for single-type deposits. They generally focus on the determination of calcium carbonate and calcium fluoride while not accounting for the calcium sulphate phase. Consequently, their applicability is somewhat constrained, and they may encounter challenges when applied to complex fluorite ore systems containing gypsum. In this study, sodium chloride was employed to separate calcium sulphate, hydrochloric acid was used to isolate calcium carbonate, and a boric acid–hydrochloric acid mixture was applied to dissolve calcium fluoride from the residue. An analytical method was developed for the sequential determination of calcium sulphate, calcium carbonate, and calcium fluoride in gypsum-associated fluorite ores by inductively coupled plasma optical emission spectrometry (ICP-OES). The separation and determination conditions for each phase were systematically investigated. Three gypsum-associated fluorite samples were analyzed in parallel according to the proposed method, yielding relative standard deviations (RSD, n = 7) of ≤4.84% for all three phases. The standard addition method was applied for recovery testing, with recovery rates ranging from 90.5% to 98.0%. This method enables the separation and continuous determination of calcium sulphate, calcium carbonate, and calcium fluoride phases. With a straightforward process and efficient operation, it saves time, labor, and costs, thereby significantly enhancing analytical efficiency. The technique is particularly applicable for phase analysis of calcium in gypsum-associated fluorite ores.