ABSTRACT
Electronic waste has become a global concern, as it has been steadily increasing over the years. The lack of regulation and appropriate processing facilities has rendered these wastes an environmental hazard. However, they represent excellent alternative sources of precious metals, which are highly in demand in various industries. Adsorption has been a popular method for metal removal/recovery because of several advantages, such as ease of use and low cost. In this regard, it is crucial to develop an inexpensive and functionalized adsorbent to selectively adsorb precious metals. Thus, silica, which is derived from rice husk and is abundantly present in Indonesia, was functionalized using an ionic liquid (SiRH_Im) and used for Au(III) adsorption from a simulated mobile phone leach liquor. SiRH_Im exhibited a high adsorption capacity (232.5 mg g-1). The Au(III) adsorption kinetic suitably fitted with the pseudo-second-order kinetic model. The Au(III) adsorption followed a chemisorption route that suited the monolayer model. Thomas' and Yoon-Nelson's models were well suited for the continuous Au(III) behavior. Selective recovery of Au(III) from SiRH_Im was achieved via sequential desorption. SiRH_Im also showed excellent reusability, as indicated by a negligible decrease in adsorptive performance over three cycles. The functionalization of silica derived from rice husk using an ionic liquid led to the successful creation of a solid adsorbent with a high adsorption capacity toward precious metals present in a simulated leach solution. Our results highlight the benefit of the functionalization of biomass through the immobilization of an ionic liquid toward the enhancement of its adsorption capability.
Subject(s)
Cell Phone , Ionic Liquids , Gold , Biomass , Silicon Dioxide , AgricultureABSTRACT
Chitosan adsorbents impregnated with a phosphonium-based ionic liquid (Chi_IL), trioctyldodecyl phosphonium chloride, were prepared for the adsorption of hexavalent chromium and compared to the performance of native chitosan. The physical and chemical properties of the adsorbents were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Effects of various parameters, such as pH, adsorbent dosage, contact time, temperature, and multi-component systems, were systematically examined. Chi_IL showed a high adsorption capacity (282.6 mg g-1) compared to native chitosan (238.1 mg g-1). The adsorption kinetics of the metals followed a pseudo-second-order kinetic model, and the experimental data were a good fit for the Freundlich isotherm model. Following the isotherm and activation energy parameter, adsorption of Cr(vi) onto Chi_IL follows a chemisorption process, possibly through an anionic exchange with the anion of the IL. The thermodynamic parameters suggested that the adsorption of Cr(vi) is a spontaneous and exothermic reaction. In the column adsorption, Chi_IL exhibited a longer column exhaustion time than that of native chitosan owing to the enhanced adsorption capacity caused by the introduction of IL. Moreover, the column with the parameters of 6 cm bed depth, 5 mL min-1 flow rate, and 50 mg L-1 was able to achieve the best performance in Cr(vi) adsorption.
ABSTRACT
Efficient and selective transport of rhodium(III) across a polymer inclusion membrane (PIM) from a 0.1 mol dm-3 HCl feed solution, also containing iron(III), to a receiving solution containing 0.1 mol dm-3 HCl and 4.9 mol dm-3 NH4Cl was achieved using a phosphonium-type ionic liquid, trioctyl(dodecyl)phosphonium chloride (P88812Cl), as the metal ion carrier. The optimum PIM composition for the Rh(III) transport was 50 wt % poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP), 30 wt % P88812Cl, and 20 wt % plasticizer 2-nitrophenyl octyl ether (2NPOE). The driving force for the Rh(III) transport was suggested to be the concentration difference of the chloride ion between the feed and the receiving solutions. More than 70% rhodium(III) could be recovered from the receiving solution, and no transport of iron(III) was observed; however, the two metal ions cannot be separated by liquid-liquid extraction. This is the first report of selective transport of rhodium(III) across a polymer inclusion membrane.
