Crude phosphoric acid is a vital component used in making phosphate fertilizers. Depending on the processes used in producing the crude phosphoric acid, it usually contains organic and inorganic contaminants. To make environmentally friendly phosphate fertilizers, these contaminants must be removed from the crude phosphoric acid stock used in making fertilizers. In this paper, commercially available strong cation exchange resin, Marathon C, was used to study the adsorptive removal of U(IV), Mn(II), Cd(II), Zn(II), and Cu(II) from synthetic multi-component phosphoric acid solutions and commercial crude phosphoric acid. Important parameters on the adsorption process such as the effects of contact time, initial metal ion concentration, sorbent dose, and concentration of phosphoric acid were investigated. The results suggested that the adsorption process reached equilibrium within 240 min for the five metal ions studied and the resin had adsorptive affinity for the metal ions in the order of U(IV) > Zn(II) > Cu(II) > Mn(II) > Cd(II). The results from the kinetics and isotherm models from the studies are very consistent with pseudo-second-order kinetic and Langmuir isotherm models. Simultaneous adsorptive removal of metal ions from the crude phosphoric acid strongly suggests that the Marathon C resin could be used in removing toxic metal ions from crude phosphoric acids used in making phosphate fertilizer.