A comparison is presented of cobalt and chromium uptake on different clays. It is shown that clay minerals are good adsorbents for cobalt and chromium in waste effluents. The sorption of cobalt and chromium on the clays studied was by ion exchange and surface complex formation, respectively. In addition, the percentage of either cobalt or chromium removed in a mixed solution environment is higher than the individual adsorption in single-component experiments. This proves a synergistic mechanism. The optimum uptake of each metal ion from mixed species was achieved by montmorillonite clay in the calcium form.