EFFECT OF OPERATING PARAMETERS ON SELECTIVE SEPARATION OF HEAVY-METALS FROM BINARY-MIXTURES VIA POLYMER ENHANCED ULTRAFILTRATION

Performance of continuous polymer enhanced ultrafiltration (PEUF) meth od was investigated for removal of mercury and cadmium from binary mix tures. This method includes the addition of polyethyleneimine (PEI) as a water soluble polymer to bind the metals, which was followed by ult rafiltration operation performed on both laboratory and pilot scale sy stems. The influence of various operating parameters such as temperatu re, metal/polymer ratio, presence of calcium ions and pH on retention of metals and permeate flux was investigated. To investigate the possi bility of selective separation of mercury and cadmium, experiments wer e conducted for binary solutions at different pH and loading ratios. I t was seen that the retention of mercury decreased and permeate flux i ncreased when the temperature increased. The increased pH and decrease d metal/ polymer ratio, loading (L), resulted in higher retention of b oth metals. Shapes of retention vs. pH or L curves were very similar f or both metals. Retentions stay almost constant at a value very close to unity until a critical L or pH value was reached, then, R decreases almost linearly with L or pH. However, retention of cadmium was affec ted more than that of mercury as the pH decreased and L increased. Thi s leads to the selective separation of mercury and cadmium. At low pH values (about 5) and at high L values (about 0.3), mercury was removed by ultrafiltration operation while almost all cadmium passed through the membrane. At pH 5.5 and cadmium/polymer ratio about 0.35 and mercu ry/polymer ratio about 0.39, the highest separation factor was obtaine d as 49. (C) 1998 Elsevier Science B.V.