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 degrees 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. (C) 2010 Published by Elsevier Ltd.