Highly effective and selective adsorption of Au(III) from aqueous solution by poly(ethylene sulfide) functionalized chitosan: Kinetics, isothermal adsorption and thermodynamics

The gold recovery from wastewater is not only beneficial to environmental protection, but also to alleviate the shortage of resources. Chitosan is considered as an excellent adsorption material, but its application in gold recovery is always some shortcomings including low adsorption capacity and selectivity. This work developed an efficient biosorbent (CS-ES) by functionalizing chitosan with poly(ethylene sulfide) for gold recovery from simulated wastewater. The properties and adsorption mechanism of CS-ES were investigated using SEM, EDS, XRD, FT-IR, BET and XPS. The results of experiments revealed that the adsorption efficiency of CS-ES for Au(III) reaches more than 90% in a wide pH range (2.0–6.0) and the highest adsorption efficiency about 99.07% was achieved at pH = 5.0. At 318 K, the highest adsorption ability of CS-ES for gold ions was 657.49 mg/g. The adsorption findings supported the Langmuir and pseudo-second-order models, suggesting that monolayer chemisorption is the dominant adsorption mechanism. The thermodynamic performance (ΔH° and ΔS° > 0, ΔG°<0) showed that gold ion adsorption by CS-ES is spontaneous exothermic reaction. CS-ES shows an excellent reproducibility after four adsorption-desorption cycles and selectivity against six metal ions. Moreover, a variety of physicochemical and spectroscopic tests demonstrate the extremely effective adsorption and in-situ reduction of gold by CS-ES are based on electrostatic attraction, chelation, and reduction between gold and nitrogen/sulfur groups. In this work, a novel adsorbent for recovering Au(III) from wastewater was devised with great efficiency, selectivity and repeatability.