Water recovery from inorganic solutions via natural freezing and melting

Abstract

A combined natural freezing and melting water separation and recovery process was evaluated qualitatively for a 0.5 m 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. The solid produced at equilibrium, consisting of ice and entrapped solution or solute crystals, was removed and melted at either 25, or 80 °C. The resulting liquid was analysed for magnesium content. 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 magnesium concentration of 6.6 times less than the initial. This is because during melting, entrapped solution drains from the solid faster than the ice melts, increasing liquid concentration at earlier stages of melting.