A Novel Process for the Production of Gold Micrometer-Sized Particles from Secondary Sources

Abstract

A novel method for the production of gold micrometer-sized particles from secondary sources is presented. The method consists of the leaching of gold using dimethyl sulfoxide (DMSO, (CH 3 ) 2 SO) solutions containing copper chloride (CuCl 2 ) followed by the precipitation of gold with hydrochloric acid (HCl). Gold was dissolved in a DMSO solution with 0.10.2 M CuCl 2 and 00.3 M sodium chloride (NaCl) at 343 K. The precipitation of dissolved gold was performed by the addition of HCl, during which the effects of the concentration of the Cl ¹ ion was investigated. It was found that the initial gold dissolution rate in DMSO solutions with CuCl 2 was up to 14.8 mg cm ¹2 h ¹1 , which was larger than the rates obtained with other leaching methods, but smaller than the author's previous research using copper bromide (CuBr 2 ) and potassium bromide (KBr). A gold recovery efficiency of up to 92.6% was obtained by precipitation with HCl solution. We obtained "raspberrylike" or "confeito-like" gold microspheres under the condition of less than 1.5 M of Cl ¹ ion and over 0.013 M of dissolved gold. Our results demonstrated that a circulating system for gold leaching and recovery and production of functional material could be developed, which would offer a number of advantages, including eco-friendliness, easy operation, low costs, and minimization of chemical sludge production.

<i>In-Situ</i> Observation for Formations of Gold Micrometer-Sized Particles in Liquid Phase Using Atmospheric Scanning Electron Microscopy (ASEM)

“…As mentioned before, by using current experimental conditions, it has been shown in the previous report 6) that liquid-phase reduction has resulted in the precipitation of spherical-shaped gold particles 6) . Accordingly, gold was precipitated using the same protocol using DMSO solvent and hydrochloric acid aqueous solution, and was subsequently ltered, washed and dried.…”

“…In this study, precipitation experiments of gold particles were carried out by using two solvent combinations that are expected to precipitate spherical and confeito-like gold particles 6) . The prepared solvents are shown in Table 1.…”

“…For further con rmation, gold was subjected to liquid-phase reduction by using a previously reported solvent system. The particles were then ltered, washed and dried by the same technique as reported before 6) . Finally, the shape of the particle of precipitation was observed using SEM (JSM-6510A).…”

“…Moreover, the precipitation time for the liquid-phase reduction of gold can be readily controlled from 1 to 30 min, and the produced particles can be observed by scanning electron microscopy (SEM). Thus, the gold particles were formed through nucleation and particle growth, and it is also suggested that the latter stops when the reduction time reaches around 30 min 6) . In our previous work 6) , we reported the liquid-phase reduction of gold, and subsequent ltering and drying of gold particles.…”

“…Thus, the gold particles were formed through nucleation and particle growth, and it is also suggested that the latter stops when the reduction time reaches around 30 min 6) . In our previous work 6) , we reported the liquid-phase reduction of gold, and subsequent ltering and drying of gold particles. However, by utilizing a conventional SEM, the state of the gold particles or the particle growth kinetics could not be observed directly.…”