Adsorptivity and selectivity of heavy metals Cd(II), Cu(II), and Zn(II) toward phosphogypsum

The phosphogypsum (PG) is a waste by-product of the wet process of phosphoric acid production. In this study, phosphogypsum was prepared and used as an adsorbent for the removal of cadmium, copper, and zinc ions from aqueous solutions. First, the phosphogypsum was characterized, before and after the adsorption process, by Fourier transform infrared spectroscopy and scanning electron microscopy. Then the effect of the initial pH of the metal ions solutions on the adsorption process has been studied. Second, the competitive adsorption of metal ions on phosphogypsum in the ternary mixture was investigated and compared with non-competitive adsorption. The results show that the adsorption of metal ions by phosphogypsum depends on the solution pH. The selectivity order of the adsorbent is Cd2+ > Cu2+ > Zn2+. From these results, it can be concluded that the phosphogypsum could be a low-cost material for heavy metals removal, especially cadmium ion, from aqueous basic solutions.