Selective recovery of Ag(I) from effluent using 2,5-dimercapto-1,3,4-thiadiazole modified apple pomace

The massive emissions of Ag(I)-containing effluent from various industries have caused huge stress to the aquatic environment, due to which, the World Health Organization (WHO) has classified silver as one of the most harmful pollutants in water bodies. The recovery of Ag(I) from various Ag(I)-containing effluents is both economically and environmentally significant. In this study, an apple pomace (AP)-based and 2,5-dimercapto-1,3,4-thiadiazole (DMTD)-immobilized bio-sorbent (DMTD-AP) was synthesized and characterized to enrich and recover Ag(I) from Ag(I)–Cu(II)–Pb(II)–Zn(II)–NI(II) effluent that contained 218.1 mg L−1 of Ag. The batch adsorption indicated that DMTD-AP could selectively adsorb 99.3% of Ag with a dosage of 5.67 g L−1 at the pH of 3.0 and temperature of 25 °C. The fixed-bed adsorption further confirmed that DMTD-AP could separate and enrich Ag(I) from the same effluent, and exhibited good durability after five cycles. The adsorption isotherms showed that the maximum adsorption capacity of DMTD-AP for Ag was as high as 196.9 mg g−1 at 25 °C. The adsorption kinetics based upon empirical and first-principle models of mass transfer indicated that the adsorption of Ag(I) on DMTD-AP was dominated by chemisorption through coordination, whereas the homogeneous solid diffusion (HSD) model could describe the mass transfer resistance during biosorption.