Rapid and selective recovery of Ag(I) from simulative electroplating effluents by sulfydryl-rich covalent organic framework (COF-SH) with high adsorption capacity

The aim of current work was to explore a new material for the fast, efficient and selective recovery of precious metal silver (Ag(I)) from electroplating effluents to alleviate its high consumption and mitigate its environmental pollution. In this study, the sulfydryl-rich covalent organic framework (COF-SH) was prepared by solvothermal method. Its Ag(I) adsorption performance was evaluated by batch adsorption experiments that the effects of initial Ag(I) concentration, ratio of adsorption dosage to solution volume, adsorption time and reacting temperature were studied. The isothermal data fitted well with the Langmuir model and the maximum adsorption capacity at 298 K was up to 609.89 mg/g. The adsorption rate was very fast almost achieving adsorption equilibrium within 16 min. The adsorption rate and adsorption capacity increased with the increase in reaction temperature. The perfect fitting with pseudo-second-order kinetic model indicated the adsorption process was dominated by chemisorption process. Weber–Morris intraparticle diffusion model divided the adsorption process into three stages and temperature had a positive correlation with the first stage, external surface diffusion. The thermodynamic fitting results suggested that the adsorption process was endothermic, disordered and spontaneous. In terms of application, COF-SH achieved highly selective adsorption of Ag(I) in simulated electroplating wastewater with coexistence of multiple metal ions, especially at high acidity (≥1 M HNO3), and the increase in concentration of competing ions had no affects. In addition, 1 M HNO3 + 0.3 M thiourea (TU) could be used as desorption agent with 100% Ag(I) desorbed from the adsorbed adsorbent COF-SH-Ag.