Continuous column adsorption of lead (Pb) and cadmium (Cd) was studied using pH adjustment and calcium-saturated montmorillonite in a short stainless steel column. Changing either pH or flow rate, while keeping inlet concentration of the ions constant, led to considerable changes in effluent concentrations and breakthrough curves (BTCs). At low pH values (2-4), H+ ions competed strongly with lead and cadmium ions; at intermediate pH (4-6), ionic size played the major role in adsorption and ion exchange and at high pH (6-9) precipitation was the major process taking place especially for lead sorption. At low flow rates less than 0.5 cm(3) min(-1), sorption of both lead and cadmium increased due to the long retention time in the column. When both lead and cadmium ions were present in the feed, adsorption remained the same while that of cadmium decreased compared with single ion experiments. (C) 1999 Society of Chemical Industry.