Selective recovery of precious metals by persimmon waste chemically modified with dimethylamine.
ABSTRACT Persimmon waste was chemically modified with dimethylamine (DMA) to obtain a tertiary-amine-type gel, named DMA persimmon waste gel (DMA-PW). It was found to be effective for the adsorption of Au(III), Pd(II), and Pt(IV) in hydrochloric acid medium. In contrast, base metals such as Cu(II), Zn(II), Fe(III), and Ni(II) were not practically adsorbed. The formation of ion pairs of the metal chloro complex anions with the protonated adsorption gels was proposed as the main adsorption process. The gel exhibited selectivity only for precious metals with a remarkably high capacity for Au(III), i.e., 5.63 mol/kg dry gel and comparable capacities, i.e., 0.42 and 0.28 mol/kg for Pd(II) and Pt(IV), respectively. According to the kinetic and electrochemical studies, the adsorption rate of Au(III) was greatly enhanced by the chemical modification. Also, its excellent adsorption characteristics for the precious metals were confirmed by adsorption and elution tests using a column packed with the DMA-PW gel.
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ABSTRACT: Adsorption of precious metals in acidic aqueous solutions using thiourea modified magnetic magnetite nanoparticle (MNP-Tu) was examined. The MNP-Tu was synthesized, characterized and examined as a reusable adsorbent for the recovery of precious metals. The adsorption kinetics were well ﬁtted with pseudo second-order equation while the adsorption isotherms were ﬁtted with both Langmuir and Freundlich equations. The maximum adsorption capacity of precious metals for MNP-Tu determined by Langmuir model was 43.34, 118.46 and 111.58 mg/g for Pt(IV), Au(III) and Pd(II), respectively at pH 2 and 25 °C. MNP-Tu has high adsorption selectivity towards precious metals even in the presence of competing ions (Cu(II)) at high concentrations. In addition, the MNP-Tu can be regenerated using an aqueous solution containing 0.7 M thiourea and 2% HCl where precious metals can be recovered in a concentrated form. It was found that the MNP-Tu undergoing seven consecutive adsorption-desorption cycles still retained the original adsorption capacity of precious metals. A reductive adsorption resulting in the formation of elemental gold and palladium at the surface of MNP-Tu was observed.International Journal of Molecular Sciences 01/2013; 14(5):9834-9847. · 2.46 Impact Factor
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ABSTRACT: Glutaraldehyde (GA)-crosslinked chitosan beads (GA-CS) are prepared with coagulating solution containing sodium tripolyphosphate and GA, and used for the adsorption of metals from binary-metal solution Au(III) and Pd(II). GA-CS exhibited selective sorption of Au(III) in the Au(III)-Pd(II) mixture. X-ray diffraction analyses showed that Au(III) was reduced to Au(0) following sorption, while Pd(II) was present as unreduced divalent form. Increased GA led to more selectivity toward Au(III), indicating that Au(III) selectivity is attributed to reduction-couple sorption of Au(III) with a reducing agent GA. Furthermore, a 2-step desorption process enabled selective recovery of Pd and Au using 5M HCl and 0.5M thiourea-1M HCl, respectively, leading to pure Pd(II) and Au(III)-enriched solutions. This finding may open a new way to design reduction-coupled selectivity-tunable metal sorbents by combination of redox potentials of metal ions and reducing agents.Journal of hazardous materials 01/2013; 248-249C:211-218. · 4.14 Impact Factor
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ABSTRACT: Because of the increase in needs for platinum group metals, as well as their low availability in nature and their environmental concerns, it is getting more urgent to separation and recovers them from dilute solutions. In this research, commercial activated carbon was used to optimize the palladium and platinum removal by applying the Taguchi approach. According to the results, the optimum operating conditions for palladium and platinum removal by activated carbon were pH = 2, particle size of adsorbent = 0.21 mm and adsorbent dose = 10 g/L. Under these optimum operating conditions, more than 98% of palladium and platinum were removed by activated carbon in 3 h. The equilibrium adsorption data were well described by the Langmuir and Freundlich models. While commercial activated carbon had the palladium and platinum adsorption capacity of 35.7 and 45.5 mg/g, respectively, the bio-polymer modified activated carbon was able to adsorb 43.5 and 52.6 mg/g of palladium and platinum, respectively. It was observed that the adsorption kinetics of palladium and platinum on these adsorbents could be well analyzed with pseudo-second-order model.Journal of the Taiwan Institute of Chemical Engineers 09/2012; 43(5):696–703. · 2.08 Impact Factor