In the present study, the effects of competitive cations NH4+, K+, Ca2+, Na+, Mg2+ and Li+ and co-anions Cl- and Br- on ion exchange of heavy metals Pb2+, Fe3+, Cr3+ and Cu2+ on clinoptilolite is examined. The presence of cations and anions in the solutions of heavy metals is reducing the removal of the latter and the order of decreasing negative effect is the following: NH4+ > Mg2+ > Ca2+ > Na+ > K+ > Li+ and Br- > Cl- for Pb2+ NH4+ > K+ > Ca2+ > Na+, Mg2+ approximate to Li+ and Br- > Cl- for Cr3+, NH4+ > K+ > Na+ > Ca2+ > Li+ > Mg2+ and Cl- > Br- for Fe3+ and Ca2+ > NH4+ > Li+ > K+ > Na+ > Mg2+ and Cl- > Br- for Cu2+. In all cases, the selectivity of clinoptilolite for heavy metals is the following: Pb2+ > Fe3+ > Cr3+ >= Cu2+. (C) 2005 Elsevier B.V. All rights reserved.