Mineral recovery from inland reverse osmosis concentrate using isothermal evaporation

Mineral recovery from reverse osmosis (RO) concentrate after concentration by a secondary sea water-type RO system with lime–soda pretreatment was the focus of this study. Lime–soda pretreatment removed Ca, Mg and Si allowing for the application of sea water-type RO resulting in a concentrate composed of sodium, potassium, sulfate and chloride. The overall objective was reduction in concentrate volume that will require disposal by evaporation while producing by-products with potential resale value. Thermodynamic phase equilibrium calculations using Pitzer’s correlations for 25 °C, accurately predicted the solubility and evaporation path of the sodium sulfate minerals as potential by-products. Bench-scale evaporation experiments verified the model predictions and indicated that 81–88% of the sodium sulfate by-products were Na2SO4.