A comparison between ferrochrome slag and gold mine tailings based geopolymers as adsorbents for heavy metals in aqueous solutions: Analyzing reusability and sustainability

Ferrodirome slag (FeCr-GP) and gold mine tailings (GMT-GP) based geopolymers were synthesized and used as adsorbents of heavy metals in aqueous solutions. Batchwise adsorption experiments were used to determine the effect of solid loading (S/L), temperature and time on the adsorption of Cu, Ni and Mn. X-ray diffraction studies showed that GMT-GP was amorphous with calcium aluminium silicate hydrate as the geopolymerization product leading to an increased surface area while GMT-GP had a significant reduction in the intensity of crystalline peaks as compared to the precursor. FeCr-GP could adsorb above 99% of the metal ions (Cu 2+ , Ni 2+ and Mn 2+ ) in solution with an initial metal concentration of 400 ppm at 298, while GMT-GP could only adsorb at least 98% of the metal with an initial metal concentration of 200 ppm. The adsorption was accompanied by a pH rise from 2.3 to 4.5 and 4.8 for GMT-GP and FeCr-GP, respectively. The maximum adsorption capacity of FeCr-GP was double that of GMT-GP. FeCr-GP could be desorbed using HCl and reverse osmosis water and could be used for a further three cycles without significant loss in adsorbing ability, while desorption of GMT-GP resulted a reduction in adsorption capability.