Effective and Selective Recovery of Precious Metals by Thiourea Modified Magnetic Nanoparticles

Tai-Lin Lin,Hsing-Lung Lien

doi:10.3390/ijms14059834

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.

Highlights

Electrical and electronic wastes (e-wastes) have been recognized as a one of the priority issues of environmental protection since a fast pace of electrical and electronic products was created by the rapid advances of e-technology in the modern society [1]
We developed thiourea modified magnetic magnetite nanoparticles (MNP-Tu) for magnetic separation and recovery of precious metals from acidic aqueous solutions
Characterization of Magnetic nanoparticles (MNPs)-Tu was conducted by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR) and Brunauer-Emmett-Teller (BET) surface analysis

Summary

Introduction

Electrical and electronic wastes (e-wastes) have been recognized as a one of the priority issues of environmental protection since a fast pace of electrical and electronic products was created by the rapid advances of e-technology in the modern society [1]. The e-wastes generally contain high value precious metals such as gold, platinum and palladium and recycling and reuse have become one of the promising options for the treatment of the e-wastes [2]. The aqua regia leachate requires further separation and recovery for collecting the precious metals. The technologies that possess the high selectivity and adsorption capacity towards precious metals are needed. The surface modified MNPs with specific functional groups such as dendrimer and dimethylamine have been tested for removal of heavy metals because of their high adsorption capacity, short adsorption time and the easy separation of metal-loaded MNPs by applying an external magnetic field [11,14]. Functional groups containing sulfur and nitrogen donor atoms are highly selective towards precious metals based on the theory of hard and soft acids and bases (HSAB theory) by Pearson [16]

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