Development of technology for obtaining high-purity sodium chloride with induced impurity removal and process modeling

Abstract

High-purity NaCl is required for chemical processes. Halite from the South Kazakhstan Bakhyt Tany deposit contains CaSO₄ and Ca²⁺/Mg²⁺ that degrade quality and operability. The article presents statistical processing and modeling of impurity deposition with phosphate ions using an automated calculation process. A stoichiometric amount of Na₃PO₄ was added to the NaCl 315 mol/dm³ brine, stirred for 25-30 minutes, precipitated for 30 minutes, and filtered. Sulfate was quantified by barium-sulfate turbidimetry; residual Ca²⁺/Mg²⁺ in the filtrate was measured titrimetrically. The Excel 2000 workbook performs coefficient estimation, significance testing, model adequacy testing, and error analysis. Response optimisation is also carried out through protected input fields. The resulting second-order models are adequate within the studied range of factors, reflect significant main effects and interactions, and predict optimal process modes, which have been confirmed experimentally. Under optimized conditions, removal reached 99.9% for Ca²⁺ and 99.8% for Mg²⁺. Sulfate ions remained at trace levels in the NaCl product. The framework enables reproducible parameter selection and provides a basis for integrating near-zero-waste handling of co-products in subsequent process design.