Increased Recovery of Gold Thiosulfate Alkaline Solutions by Adding Thiol Groups in the Porous Structure of Activated Carbon

Abstract

Thiosulfate leaching combined with ion-exchange resins is an innovative alternative for gold recovery. According to the properties of activated carbon, it could replace resins in the gold recovery process, improve efficiency, and reduce operating cost. In this research, the adsorption process of gold thiosulfate complex on thiol-modified activated carbon was studied. Thioglycolic acid (ATG) was impregnated in activated carbon, and its adsorption ability was tested with synthetic solutions of gold and sodium thiosulfate (Au 10 mg·L−1, Na2S2O3 0.1 mol·L−1, pH = 10.0). Carbon was characterized by infrared spectroscopy, SEM-EDS, PZC titration, hardness number measures, and proximal analysis. Synthetic solutions were also characterized by UV-vis spectroscopy and cyclic voltammetry. The percentage of volatile material increased from 10.0 to 13.9% due to the impregnation process of ATG. Infrared spectra show characteristic bands of C-H, S-H, and C-S bonds. In the adsorption tests, the ATG-impregnated carbon achieved 91% of gold recovery, while the same amount of ATG in the liquid phase stirred with unmodified activated carbon reached 90% of gold recovery. The 44.9% of gold recovered with activated carbon impregnated with ATG was eluted with sodium cyanide ([NaCN] = 0.2 mol·L−1; [NaOH] = 0.25 mol·L−1; [CH3CH2OH] = 30% V/V; pH = 12.0; t = 24 h). These results suggest the gold transferred from the thiosulfate complex to a new gold thiolate complex.

Kinetic and Thermodynamic Studies of Precious Metals Sorption on Impregnated Lewatit VP OC 1026 from Chloride Solutions

“…In order to investigate kinetics of sorption of gold(III), platinum(IV) and palladium(II) ions on Lewatit VP OC 1026-Aliquat 336, the sorption kinetic models: pseudo-first-order (2), pseudo-second-order (3) and diffusion models as well as intra-particle diffusion model ( 4) and Dunwald-Wagner model (5) were used. Linear forms of these models are described by: ln q e À q t ð Þ ¼ lnq e À k 1 � t ðPFOÞ (2) q e = 0.8 mg/g Au(III) [25] XAD-7 impregnated by IL101 C = 0.01 M HCl, Agitation time: 7 days; q e = 87.9 mg/g Au(III) [26] XAD-1180 impregnated by IL101 C = 0.01 M HCl, Agitation time: 7 days; q e = 126 mg/g Au(III) [26] N-(diethylthiophosphoryl)-aza [18]crown-6 immobilized into Amberlite XAD-4 resin C = 0.05 M HCl q e = 42 mg/g Au(III) [27] Amberlite XAD-7 resin with a phenanthroline-derived diamide extractant N,N'diethyl-N,N'-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen) C = 3 M HNO 3 q e = 74.6 mg/g Au(III) [28] XAD7HP impregnated by 2-mercaptobenzoxazole (MBO)/XAD7HP C = 0.5 M HNO 3 q e = 98.4 mg/g Pd(II) [29] Chitosan with dibenzo-18-crown-6-ether (Chitosan-DB18 C6) C o = 150 mg/L Pd(II), pH = 2 C o = 175 mg/L Pt(IV), pH = 2 q e = 17.6 mg/g Pd(II) q e = 98.4 mg/g Pt(IV) [30] Amberlite XAD7 functionalized with dibenzo-18-crown ether-6 (XAD7-DB18 C6) pH = 2, T = 298 K q e = 6.5 mg/g Pd(II) [31] Alginate-Cyanex 302 microcapsules 0.5 M HCl, T = 293 K q e = 22.1 mg/g Pd(II) [32] Monomer-impregnated adsorbent (MTCA XAD7) C o = 850 mg/L Pd(II), C = 1 M HCl q e = 7.9 mg/g Pd(II) [33] 2,2'-thiobisethanol dimethacrylate/ ethylene glycol dimethacrylate copolymer C = 4 M HCl q e = 100 mg/g Au(III) [34] Purogold™ A194 resin C = 1 M HNO 3 , T = 294 K q e = 0.76 mmol/ g Pd(II) [35] Lewatit VP OC 1026 impregnated by Aliquat 336 C = 0.1 M HCl, Agitation time: 24 h, T = 293 K, m:V = 0.1 g : 25 cm 3 q e = 94.1 mg/g Au(III) q e = 38.2 mg/g Pd(II) q e = 36.2 mg/g Pt(IV)…”

Application of Response Surface Methodology (RSM) for Simultaneous Optimization of Kinetic Parameters Affecting Gold Leaching in Thiosulfate Based Media: A Statistical Approach

“…is has given dawn to the development of several other gold extraction methods with di erent substitute reagents for cyanide such as thiosulfate, thiocyanate, thiourea, halides, and bisul de [7]. Amongst the aforementioned methods, gold leaching in thiosulfate media has been mostly developed and carried out due to the fact that it is regarded as an environmentally friendly and cost-e ective process with high gold extraction e ciency [8,9]. e overall redox reaction for gold leaching in the dissolved oxygen-thiosulfate system is given as follows [10]:…”