Adsorption of Ag(I) on chelate resins containing N and S: Comparison and computational study with anionic resin

Chelate resins containing N and S atoms have a strong affinity for silver ions Ag(I). In order to compare the effects of different functional groups on adsorption performance, two thiourea based isomeric resins containing S and N atoms (D840 and TMMR) were applied. And considering the silver-containing wastewater in photography, a thiosulfate system and tertiary amino anion resin D301 were used to compare the influence of external factors and specific adsorption mechanism. The adsorption properties were conducted using static experiments. FTIR, FESEM, BET and XPS were used to analyze the resins before and after adsorption. Thermodynamic and kinetic model fitting and DFT theoretical calculations were also carried out. Acidic conditions (pH = 2.0 to 5.0), adsorption dose of 1.5 g/L and reaction time (10-12 h) are beneficial for Ag(I) adsorption. The adsorption of Ag (I) by resins are more consistent with Langmuir isothermal adsorption model and pseudo-second-order kinetic adsorption model. Inferring from DFT calculation that the adsorption is mainly due to the chelation of S and N and the protonation of N. TMMR prepared by grafting thiourea onto the chlorine sphere matrix has the strongest activity, which is consistent with the experimental results that its maximum adsorption capacity could reach 602.1 mg/g under room temperature, exhibiting excellent application potential. It was inferred that dual mechanism of chelation and N protonation can exhibit better adsorption performance compared to a single action, but chelation has slightly poorer cycling stability compared to N protonation. This work mainly lies in the systematic comparison of Ag(I) adsorption on chelate resins and anionic resin, and the study of adsorption mechanism by combining DFT theoretical calculation, forming a complete closed-loop research system and enriching the analysis process.