The paper discusses the application of natural zeolites from clinoptilolite group for mercury removal from industrial effluents from copper smelter and refinery. The experiments included studies on sorption mechanisms (adsorption or ion-exchange) and sorption equilibria. The dominating mechanism of sorption with zeolite was found to be ion exchange and the maximum sorption capacity was evaluated as 1.21 meq/g sorbent. Three cation-exchange groups were identified and deprotonation acidity constants (pK(a)) 3.1 7.3 and 10.7 were determined. The results of model experiments were verified by the treatment of the industrial effluent containing elevated levels of Hg2+ ions on the laboratory as well as on full-plant scale. Laboratory and industrial scale experiments showed that zeolite was capable of mercury ions removal from the effluent. Currently, the company uses the proposed method for effluents treatment. (C) 2004 Elsevier Ltd. All rights reserved.