In the present study, the adsorption of cadmium on phosphogypsum, a waste material from the manufacture of phosphoric acid by wet process, was studied. Before batch adsorption study, phosphogypsum was pre-conditioned by milk of lime. Effect of initial pH on cadmium adsorption was investigated. It was found that cadmium adsorption was dependent on solution pH and maximum cadmium removal was observed in the pH range of 9.5 and 11.5. The Langmuir and Freundlich theories were used to describe the cadmium adsorption process, and the Freundlich isotherm showed the best fit to the process. Maximum adsorption capacity of lime-preconditioned phosphogypsum was found to be 131.58 mg/g. (C) 2007 Elsevier B.V. All rights reserved.