Water Recovery from Inorganic Solutions via Natural Freezing and Meltin

A combined natural freezing and melting water recovery process was evaluated for a 0.5 molal magnesium sulphate solution. 500 mL of solution was placed in a container open to the air, and the temperature was lowered to between --2 and --26 °C. At equilibrium the solid produced, consisting of ice and entrapped solution or solute crystals, was removed and thawed at either 3 °C or 25 °C. The resulting liquid was analysed for magnesium. Microscopy of the solid was also performed. Although the purity of the liquid was not affected by the thawing temperature, solid frozen at --26 °C yielded the best purity when melted, as 40% of the original water could be recovered at a concentration of 0.075 molal magnesium sulphate. This is because during melting entrapped solution drains from the solid faster than the ice melts, increasing liquid concentration at earlier stages of melting.