Effect of precipitates in the brine on the filtration process of ceramic membrane with airlift

Brine purification with chemical precipitation is one of the key processes in chlor-alkali industry. In this paper, the influence of the chemical precipitates (CaCO₃, BaSO₄ and Mg(OH)₂) on the filtration process of ceramic membrane with the help of airlift was investigated. The results show that the aeration can significantly enhance the membrane fluxes during the filtrations of these three suspension systems. The filtration flux of CaCO₃ or BaSO₄ suspension system is more than 1.5 times of that of these Mg(OH)₂ system, and when the exposed gas volume is greater than 300 L·h^-1, the flux of CaCO₃ or BaSO₄ suspension system has little change with the further increase of the amount of aeration, but it can increase the flux of Mg(OH)₂ system more than 50%. The fluxes of the above three systems basically increase linearly with the increase of the transmembrane pressure. Since the solid content increase will cause the significant increase of the system viscosity, the membrane fluxes of these three systems show a decreasing trend with the solid content increase. The brine sediment analysis results show that the calcite phase of CaCO₃ particles uniformly disperse with the particle size of 16.08 μm and the surface potential of -16.5 mV; the barite phase BaSO₄ particle size is about 2.18 μm and the surface potential is -33 mV; the amorphous Mg(OH)₂ particle size distribution is wide with an average particle size of 1.59 μm and surface potential of -18 mV. Because of the effects of both the size and surface charge of the particles, the membrane filtration resistances of CaCO₃ and BaSO₄ suspension systems are similar, but they are far different from that of Mg(OH)₂ suspension system. It was found that, in the co-precipitation process of the system consisted of calcium and magnesium ions, the membrane filtration flux increases with increasing the portion of calcium ion.