PHOSPHATE REMOVAL FROM WATER BY RED MUD USING CROSS-FLOW MICROFILTRATION

Red mud (which is a waste material formed during the production of alu mina and primarily contains ferric and aluminium oxides) was used as a n adsorbent for the removal of phosphate ions from water using crossfl ow microfiltration. it is shown that phosphate ions act as a coagulant for red mud particles, forming a compressible cake with a compressibi lity index of unity. As shown also by dead-end filtration experiments, the cake resistance decreases with increasing phosphate concentration . The phosphate rejection is a strong function of feed dispersion pH, phosphate and red mud concentration ratio as well as the concentration of co-ions such as sulphate ions used to adjust the dispersion pH. Un der certain conditions, especially when pH = 5.2, steady state permeat e flux and phosphate rejection reach a maximum with 100% rejection ach ievable. The permeate also contain metal ion impurities originating fr om red mud and their concentrations increase with increasing red mud c oncentration and decreasing pH. The effects of other process variables , crossflow velocity and membrane pore size on phosphate rejection and permeate flux are also studied. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.