Application of Response Surface Methodology to Optimise Industrial Salt Production

Abstract

Common salt is mainly composed of sodium chloride (NaCl) with several impurities, such as calcium sulphate (CaSO₄), magnesium sulphate (MgSO₄), and magnesium chloride (MgCl₂). Conventional salt purification is commonly carried out through recrystallisation. However, this method requires a double crystallisation process, and each evaporation stage may take 3–4 weeks when solar evaporation is used. Therefore, this study aims to develop a faster method for producing high-purity sodium chloride (NaCl) without double crystallisation. Chemical precipitation was selected as an alternative method to remove impurities from salt. In this process, sodium carbonate (Na₂CO₃) is used to remove Ca²⁺, sodium hydroxide (NaOH) is used to remove Mg²⁺, barium chloride (BaCl₂) is used to remove SO₄²⁻, while anionic flocculant and sodium sulphite (Na₂SO₃) are used to assist sludge removal. The concentrations of these chemicals were optimised using response surface methodology (RSM). The NaCl percentage was analysed using an XRF instrument. The optimum conditions were 0.3% Na₂CO₃, 0.2% BaCl₂, 0.061% NaOH, 5% Na₂SO₃, and 400 g/1000 L anionic flocculant, producing NaCl purity of 95.365%. Based on the RSM analysis, the recommended model was the cubic model, with an R² value of 0.979.