Removal of heavy metals from waste phosphogypsum materials using polyethylene glycol and polyvinyl alcohol polymers

Abstract

Enormous stockpiles of phosphogypsum (PG) generated during the wet process production of phosphoric acid are stored at many sites around the world and pose problems for their safe storage, disposal, or utilization. The aim of this study was to investigate the performance of two polymers polyethylene glycol (PEG) and polyvinyl alcohol (PVA) in removing heavy metal from waste PG materials with a batch reaction approach. Batch experiments showed that the adsorption capacities of PEG and PVA polymers increased quietly as a result of molecular weight with increase in active surfaces of adsorbents. It is important to note that the adsorption capacities of the PEG and PVA polymers presented in this paper vary, depending on the characteristics of the individual adsorbent, the extent of molecular weight, and the concentration of adsorbate. The maximum percentage removal with PEG of Cd, Cr, Cu, Pb, Zn, and Mo followed the order: Cu (96%)>Cr (94%)=Mo (94%)>Zn (74%)>Cd (70%)>Pb (11%), while the removal of Cd, Cr, Cu, Mo, Pb, and Zn with PVA adsorbents followed the order: Cu (95%)>Mo (93%)>Cr (91%)>Cd (84%)>Zn (78%)>Pb (10%). Obviously, PEG and PVA polymers are suitable for industrial hazardous solid waste containing Cd, Cr, Cu, Mo, Pb, and Zn contaminations. The calculated singular indices including ecological risk factors (Eri) showed that Cd should be considered a moderate potential ecological risk, while Cr, Cu, Pb, and Zn indicated a low ecological risk. The calculated integrated potential ecological risk indices (RI=∑Eri) considered that Cd, Cr, Cu, Pb, and Zn indicated pollution in all studied samples is less. Among these results, Cd, Cr, Cu, Pb, and Zn content removal using PEG and PVA polymers would be of great importance in environmental applications, and they can be considered a very suitable and efficient option for PG utilization.