Novel method for synthesizing high S-bearing hybrid sorbent for efficient silver binding – Characterization, testing, and application to metal recovery from X-ray films.

[Display omitted] • Sulfur-functionalized SiO 2 beads for highly efficient Ag(I) sorption at pH 6. • Endothermic sorption; isotherm fitted by Temkin equation (q m ; 3 mmol Ag g−1). • Fast sorption (t eq : ≈20 min); kinetics modeled by pseudo-first order rate equation. • Strong preference for Ag(I) in multicomponent solutions and X-ray film leachate. • Remarkable metal desorption with 0.3 M HNO 3 and stable recycling. The reaction of thiocarbazide with pentaerythritol tetrakis(3-mercaptopropionate) in the presence of mesoporous silica beads allows producing a composite sorbent (PTMF-SiO 2) with high affinity for silver. The high density of both N- and S-based reactive groups (about 5 mmol g−1) explains sorption capacities as high as 3 mmol Ag g−1 at pH 6. The sorption mechanisms are correlated to the pH effect, and to FTIR and XPS spectroscopic analyses. The sorption is endothermic and spontaneous, and the sorption isotherms are successfully modeled using the Temkin equation. Uptake kinetics are fitted by the pseudo-first order rate equation: the equilibrium is reached in 20–30 min. Ultrasonic treatment allows slightly increasing both kinetics (apparent rate coefficient k 1 is almost doubled) and sorption capacities (by less than 7 %). Silver (being a soft acid) preferentially reacts with soft bases; this may explain the selective removal of Ag(I) by PTMF-SiO 2 against base metals and alkali or alkaline earth metals (in multicomponent equimolar solutions). The sorbent shows remarkable recycling stability (for at least 5 cycles): complete desorption is achieved in ≈20 min with 0.3 M HNO 3 solution and the loss in sorption does not exceed 2.5 % at the fifth recycling. Finally, the sorbent is successfully applied to silver recovery from acidic leachates of spent X-ray films (from different hospitals from Hengyang, China), as a case study. Silver is selectively recovered with high efficiency (>96 %) (together with Cu(II), to a lesser extent). [ABSTRACT FROM AUTHOR]