A review of gold extraction using noncyanide lixiviants: Fundamentals, advancements, and challenges toward alkaline sulfur-containing leaching agents

Alkaline sulfur-containing lixiviants,including thiosulfate,polysulfides,and alkaline sulfide solutions,stand out as a promising class of alternatives to cyanide because of their low toxicity,high efficiency,and strong adaptability.In this paper,we summarized the research progress and remaining challenges in gold extraction using these noncyanide reagents.After a brief introduction to the preparation method,the transformation process of various sulfur-containing species in alkaline solutions was discussed.Thereafter,some insights into the mechanism of gold leaching in alkaline sulfur-containing solutions were presented from different aspects,including thermodynamics analysis,electrochemical dissolution,and leaching kinetics.Moreover,recent progress in in-situ generation of sulfur-containing anions from gold-bearing sulfide minerals was outlined as well.Gold passivation caused by sulfur species was discussed in particular because it is considered the greatest challenge facing sulfur-containing leaching systems.Alkaline sulfur-containing lixiviants are expected to serve as alternatives in industrial applications of gold extraction,particularly for refractory gold ores containing copper and carbonaceous matter.

Preparation and characterization of high-strength calcium silicate boards from coal-fired industrial solid wastes

To realize the comprehensive utilization of coal-fired industrial solid wastes, a novel high-strength board was prepared from calcium silicate slag, fly ash, and flue gas desulfurization(FGD) gypsum. The changes in mineral phases, chemical structure, and morphology during hydration were investigated by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), and scanning electron microscopy(SEM). A traditional board made from quartz and lime was prepared as a reference. The novel board not only consumes a lot of solid wastes, but also meets the strength requirement of the class-five calcium silicate board according to the Chinese Standard JC/T 564.2—2008. Microanalysis showed that hydrated calcium silicate gel(C-S-H(I)), ettringite, tobermorite, and xonotlite were successively generated in the novel board by synergistic hydration of the mixed solid wastes. The board strength was improved by the formation of tobermorite and xonotlite but decreased by unhydrated quartz. It was demonstrated that quartz was not completely hydrated in the traditional board. As a result, the flexural strength of the traditional board was much lower than that of the novel board.

Study on gold concentrate leaching by iodine-iodide

Gold extraction by iodine-iodide solution is an effective and environment-friendly method. In this study, the method using iodine-iodide for gold leaching is proved feasible through thermodynamic calculation. At the same time, experiments on flotation gold concentrates were carried out and encouraging results were obtained. Through optimizing the technological conditions, the attained high gold leaching rate is more than 85%. The optimum process conditions at 25℃ are shown as follows： the initial iodine concentration is 1.0%, the iodine-to-iodide mole ratio is 1：8, the solution pH value is 7, the liquid-to-solid mass ratio is 4：1, the leaching time is 4 h, the stirring intensity is 200 r/mim, and the hydrogen peroxide consumption is 1%.

Mineralogical characterization of copper sulfide tailings using automated mineral liberation analysis: A case study of the Chambishi Copper Mine tailings

As ore grades constantly decline,more copper tailings,which still contain a considerable amount of unrecovered copper,are expected to be produced as a byproduct of froth flotation.This research reveals the occurrence mechanism of copper minerals in typical copper sulfide tailings using quantitative mineral liberation analysis(MLA)integrated with scanning electron microscopy–energy dispersive spectroscopy(SEM–EDS).A comprehensive mineralogical characterization was carried out,and the results showed that almost all copper minerals were highly disseminated within coarse gangue particles,except for 9.2wt%chalcopyrite that occurred in the 160–180μm size fraction.The predominant copper-bearing mineral was chalcopyrite,which was closely intergrown with orthoclase and muscovite rather than quartz.The flotation tailings sample still contained 3.28wt%liberated chalcopyrite and 3.13wt%liberated bornite because of their extremely fine granularity.The SEM–EDS analysis further demonstrated that copper minerals mainly occurred as fine dispersed and fully enclosed structures in gangue minerals.The information obtained from this research could offer useful references for recovering residual copper from flotation tailings.

Aerosol flotation of low-grade refractory molybdenum ores

The characteristics of aerosol flotation, which include the effect of the concentration and particle size of kerosene aerosol on the molybdenum （Mo） flotation index and the effect of kerosene aerosol dosing method on the kerosene dosage and flotation time, were studied in the flotation of low-grade refractory molybdenum ores using kerosene aerosol. The results revealed that the particle size and concentration of kerosene aerosol had little effect on the Mo grade but had significant effect on the Mo recovery. A smaller particle size and a lower con-centration of kerosene aerosol were beneficial to the Mo aerosol flotation. For the received Mo ore samples, the optimized particle size of kerosene aerosol was 0.3-2 μm and the optimized aerosol concentration was 14 mg/L. The compressed air atomizer had a more uniform dis-tribution of aerosol particles than the ultrasonic atomizer, and the aerosol concentration was controlled easily, so the compressed air atomizer was more suitable for the research of aerosol flotation. Compared with conventional flotation in which kerosene was directly added into the ore pulp, the flotation time was reduced by ~30%, and the dosage was decreased by ~20% in aerosol flotation, while the Mo flotation index was similar.

Gold-leaching performance and mechanism of sodium dicyanamide

In this work,sodium dicyanamide(SD)was used as a leaching reagent for gold recovery,and the effects of the SD dosage and solution pH on the gold-leaching performance were investigated.A gold recovery of 34.8%was obtained when SD was used as the sole leaching reagent at a dosage of 15 kg/t.In the presence of a certain amount of potassium ferrocyanide(PF)in the SD solution,the gold recovery was found to increase from 34.8%to 57.08%.Using the quartz crystal microbalance with dissipation(QCM-D)technique,the leaching kinetics of SD with and without PF were studied.The QCM-D results indicate that the gold-leaching rate increased from 4.03 to 39.99 ng·cm^(–2)·min^(–1) when the SD concentration was increased from 0 to 0.17 mol/L,and increased from 39.99 to 272.62 ng·cm^(–2)·min^(–1) when 0.1 mol/L of PF was used in combination with SD.The pregnant solution in the leaching tests was characterized by X-ray photoelectron spectroscopy and electrospray mass spectrometry,which indicated that Au and(N(CN)2)–in the SD solution formed a series of metal complex ions,[AuNax(N(CN)2)x+2]–(x=1,2,3,or 4).

Exfoliation of poly(ethylene glycol)-intercalated graphite oxide composite in water without sonication

A novel method for exfoliating graphite oxide(GrO)was implemented through the mass water absorption of a GrO–poly(ethylene glycol)(GrO–PEG)composite.The GrO–PEG composite was prepared by intercalating PEG into the lamellae of GrO,and the variation of the basal spacing was measured by X-ray diffraction analysis.The yield of graphene was measured with an ultraviolet–visible spectrophotometer,and the properties of graphene oxide(GO)were characterized by atomic force microscopy,transmission electron microscopy(TEM),Raman spectrometry,and Fourier transform infrared spectroscopy.Increasing intercalation time was found to improve the yield of GO,whereas increasing the PEG molecular weight had the opposite effect.The GO sheets produced from the intercalation–absorption–exfoliation process were found to be a four-layer structure.TEM and Raman analyses indicate that the graphitized structure and oxygen groups of GO were preserved during the exfoliation process.Most importantly,the results show that good-quality GO could be prepared via a mild method involving water absorption of a GrO–PEG composite.

Optimization and mechanism of gold-bearing sulfide flotation

In order to overcome the difficulty of extracting gold from gold-bearing sulfide ore by cyanide process flotation was adopted based on mineralogical analysis Mineralogy shows that gold particles are of superfine structure and mainly enclosed by sulfide ores. Primary gold-bearing sulfide ore is fine-grained pyrite and arsenopyrite. The paper describes the effects of ratios and dosage of activators and collectors on the recovery and grade of gold concentrate. A proper flotation flowsheet was then proposed based on experimental condition and closedcircuit test. The gold concentrate with the gold grade of25.14 g ton-1and the recovery of 86.94 % is obtained after one rougher, three cleaners, and four scavengers from fine grinding flotation process. Furthermore, the mechanisms of combined activators and combined collectors were studied by thermodynamic calculation, and structure-activity relationship of flotation reagent was also explained