Highly concentrated KCl and MgCl2 solutions were treated with direct contact membrane distillation (DCMD). The effects of salt concentration (1.0—4.0 mol·L-1) and circulation velocity (0.1—0.5 m·s-1) on permeate flux were investigated. Permeate flux decreased with increasing concentration

which was attributed to vapor pressure reduction caused by decrease of water activity in the solution. Reversed flux occurred in the DCMD process of highly concentrated MgCl2 solution (>3.0 mol·L-1) under the test conditions

which was due to the combined effect of lower water activity and higher viscosity of the fluid. Permeate fluxes increased with increasing circulation velocity

which was more effective to reduce the negative effect of temperature and concentration polarization for MgCl2 solution with higher viscosity. Membrane distillation-crystallization (MDC) of a highly concentrated solution of KCl-MgCl2-H2O was investigated for recovery of KCl crystalline product and pure water with batch operation mode. The effect of way of cooling on supersaturation of solution

morphology

and crystal size distribution was studied. KCl crystalline product with regular shape

tidy surface and concentrated particle size distribution was obtained by natural cooling and maximum degree of supercooling generated under natural cooling was lower than under quick cooling

which was beneficial to control nucleation amount and growth rate of KCl.