Experimental studies on the retention of cadmium (Cd2+), copper (Cu2+), nickel (Ni2+), and lead (Pb2+) by bentonite samples from Iran were conducted using single- and multiple-component solutions. Based on the sorption capacity of bentonite the following order was obtained for single- and multiple-component solutions: Pb2+>Cd2+>Ni2+>Cu2+. The maximum adsorption capacities of bentonite with metals in single- and multiple-component solutions were 29.5%, 22.5%, 19.2%, and 17.1% and 13.5%, 13.4%, 12.1%, and 9.1% for Pb2+, Cd2+, Ni2+, and Cu2+, respectively. Desorption isotherms of Cd2+, Cu2+, Ni2+, and Pb2+ deviated significantly from the sorption isotherms, thereby indicating irreversible or very slowly reversible sorption. Finally, soil solution saturation indices and metal speciation were assessed using the Visual MINTEQ 2.6 program and the probability of mineral precipitation was supported by scanning electron microscopy.