L-cysteine impregnated alginate capsules as a sorbent for gold recovery

The present study deals with the development of a biosorbent for the recovery of gold with high sorption capacity. For this L-cysteine, an amino acid was encapsulated with alginate to impart solid form and mechanical stability to the sorbent in solutions, because cysteine is known to be a good chelating agent. The process of encapsulation was optimized by measuring the sorption capacities of different capsules prepared by varying the compositions of carboxymethylcellulose, cysteine, and alginate. The sorption performance of the prepared capsules was tested by carrying out batch-wise sorption studies. The sorption of gold by the capsules was modeled by Langmuir sorption isotherm. The maximum uptake of the capsules was as high as 298.2 mg/g. FTIR studies indicated the involvement of the -SH group of cysteine in the complexation reaction with gold species. Out of different eluents tested for the regeneration of cysteine capsules, a 1:1 mixture of 0.1 M thiourea in 0.1 M HCl showed the best results by desorbing 98.5% of the gold from the gold-loaded cysteine capsules. Therefore, the developed capsules can be applied to recover gold from aqueous solutions.