The behaviour of polymer depressant carboxymethyl cellulose (CMC) onto talc was investigated as a function of ionic strength of potassium, magnesium and calcium ions. The effect of molecular weight of CMC was investigated and adsorption isotherms were constructed at various experimental conditions. Adsorption isotherms clearly demonstrated the presence of a two-plateau adsorption, which was less significant at lower CMC molecular weights. A systematic increase in talc depression was observed when the molecular weight of CMC was increased. The presence of ions was found to have a favourable effect on talc adsorption, where increasing the ionic strength of Mg(2+), Ca(2+) and K(2+) from 10(-3) to 10(-2) increased the adsorption considerably. The presence of divalent cations achieved higher depression of talc in general compared to monovalent cation K(+), with Ca(2+) ions having the greatest effect. (C) 2004 Elsevier B.V. All rights reserved.