随着中国对环境保护要求的日益提高,非氰提金方法在黄金选冶工业中所占比重越来越高.对中国近年来涌现出的新型环保提金剂的种类、性能和浸金效率进行了归纳总结,并重点对该类提金剂的合成和浸金机理进行了分析探讨.提出了进一步开展新型环保提金剂合成工艺优化及浸金机理研究、不断增强其对不同类型金矿石的适应性,是该类提金剂未来推广应用的重点研究方向,以期为实现"绿色、环保、安全"的黄金选冶提供借鉴.

Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing CO2 emissions. Mine tailings (MTs) rich in Si and Al can be served as a promising precursor for geompolymer preparation only when the severe defect in the low reactivity is overcame. Alkali-hydrothermal activation technology was used to enhance the reactivity of MTs, and then activated tailings (ATs) and slag served as the precursors for the one-part geopolymer (OPG) preparation. Activation mechanism of MTs, workability, compressive strength, and hydration reactions of OPG samples were studied. The crystalline mineral phases in the MTs reacted with NaOH to form the amorphous sodium aluminosilicate, thus increasing the amorphization degree. High NaOH content favored the MTs activation, and the ATs with high NaOH content tended to create a higher initial pH and release more active species (Si and Al) for the slag hydration. The increase of NaOH content shortened the setting time, decreased the fluidity, and increased the strength of OPG samples. This was because the duration of the induction period was shortened and the hydration rate in the acceleration period of OPG samples was improved with increasing NaOH content, which generated large amounts of calcium–sodium aluminosilicate hydrate (C(N)-A-S-H) gel and yield the compact microstructure. However, excessive NaOH content resulted in a poor microstructure, and it is likely responsible for the reduction in strength.

Cyanide is currently the predominant lixiviant for gold extraction. However, cyanide is highly toxic, causing potential environmental hazards and high detoxification costs. This has initiated extensive research aimed at seeking and developing eco-friendly substitutes for cyanide. Although significant research has been undertaken, most, if not all, of the traditional non-cyanide lixiviants such as thiosulfate, thiourea, halide and thiocyanate have proven to be difficult to achieve widespread adoption at gold mines because of their inherent limitations. In recent years, a range of novel eco-friendly synthetic gold lixiviants (NESGLs) such as “Jinchan”, one of the most representative products, have been developed successfully. Compared with cyanide, these NESGLs are much less or non-toxic, and have achieved comparable gold recoveries from ores without changing the original cyanidation process and equipment. The successful development of NESGLs appears to be making significant inroads into the dominance of cyanide, as evidenced by a growing number of their industrial applications at gold mines worldwide. This paper reviews the current status of gold extraction from its ores using the NESGLs with details focused on their leaching efficacy, synthesis, and composition as well as possible leaching mechanisms. Their future perspectives and developing trends of considerable concern are also discussed.

Gold extraction from ores using non-cyanide lixiviants is currently a significant topic worldwide. Herein, we report the synthesis of an eco-friendly lixiviant that not only is much less toxic than sodium cyanide (NaCN) but also shows excellent effect in the leaching of gold. The lixiviant can be synthesized from roasting of the well mixed potassium hexacyanoferrate(II) trihydrate (K4Fe(CN)6.3H(2)O), urea (CO(NH2)(2)) and sodium carbonate (Na2CO3) with a mass ratio of 1:6:2 under the conditions of heating rate 10-15 C/min, roasting temperature 700 ?, and temperature holding time 1 h. X-ray diffraction (XRD) analysis suggested that the synthetic lixiviant contained a new phase that is efficient in leaching gold playing the role of the gold lixiviant. Gold leaching results from a gold concentrate showed that the synthetic lixiviant not only has a gold leaching efficacy comparable to NaCN but also achieves faster leaching kinetics than NaCN. Under the optimal leaching conditions of lixiviant concentration 0.3 wt%, initial pH 10-11, liquid to solid ratio 2.5:1, and agitation speed 600 rpm, the synthetic lixiviant could achieve a gold extraction of 87.0% in 8 h and 97.5% in 24 h on the gold concentrate, reducing the leaching time by 12 h compared with cyanidation (97.1% gold extraction in 36 h). In addition, the method of activated carbon adsorption was shown to efficiently adsorb almost all the gold (> 99.0%) from the leach solutions, and the barren leach solution could be reused back to the leaching stage to extract gold.

Environmental and economic issues caused by several tailings storages have attracted worldwide attention; therefore, these urgently need to be solved cost-effectively. In this study, gold mine tailings rich in Si and Al oxides were activated by an alkaline hydrothermal method for use as precursors to produce a one-part geopolymer. The results indicated that the crystalline mineral phases in tailings were partially or completely decomposed by alkaline hydrothermal activation. However, this decomposition depended heavily on the alkali content, temperature, and time. The decomposed tailings were converted to the amorphous sodium aluminosilicate reactant, thereby making tailings a reactive starting material. Subsequently, the one-part geopolymer was prepared from the activated tailings and slag by just adding water without adding any extra alkaline activator. By adding 60 wt% of slag, the one-part geopolymer with an optimum compressive strength value of 33.5 MPa at 28 days was obtained. This was much higher than that of the control sample containing raw tailings without any pretreatment. The high strength could have been because of the amorphous sodium aluminosilicate formed in the activated tailings that could dissolve in water to create alkaline conditions, which could effectively activate the pozzolanic activity of the slag. The main geopolymerization product was the glassy calcium-sodium aluminosilicate hydrate (C(N)-A-S-H) gel, which acted as a binder to closely connect the residual solid particles and form a hardened geopolymer material. (c) 2021 Elsevier Ltd. All rights reserved.

Thiosulfate is a green gold lixiviant that has promise to replace cyanide at the gold mining industry. Hex-aamminecobalt(III) (Co(NH3)(6)(3+)) is effective in catalyzing the thiosulfate leaching of gold from ores, but the electrochemical behavior and catalytic leaching mechanisms remain unclear. This paper reports an in-depth investigation into the electrochemical behavior of gold leaching in ammoniacal thiosulfate so-lutions catalyzed by Co(NH3)(6)(3+). The electrochemical results suggested that Co(NH3)(6)(3+) is more efficient than Cu(NH3)(4)(2+) in catalyzing the ammoniacal thiosulfate leaching of gold. Compared with Cu(NH3)(4)(2+), the coulombic efficiency of gold dissolution (QAu/QT) under the Co(NH3)(6)(3+) catalysis is much higher. In the presence of Co(NH3)(6)(3+), the QAu/QT was nearly 100% at 150-250 mV and higher than 78.9% at 250- 350 mV; at 250 mV, the QAu/QT was approximately 100% in the initial electrolysis of 300 s and remained basically unchanged at around 75% after 1200 s. Leaching results further showed that the catalysis of Co(NH3)(6)(3+) not only achieved a continuous leaching of gold with time, but also significantly decreased the consumption of thiosulfate from 36.5% (for Cu(NH3)(4)(2+)) to 20.9% after leaching 24 h. In the ammonia-cal thiosulfate solution, Co(NH3)(6)(3+) is likely reduced to mixed ligand Co(II) complexes of Co(NH3)x(S2O3)(0) (x = 4, 5), which are readily oxidized back to Co(NH3)(6)(3+). Thus, an improved catalytic mechanism of gold leaching is proposed that the redox cycle between Co(NH3)(6)(3+) and Co(NH3)x(S2O3)(0) (x = 4, 5) catalyzes the leaching of gold with ammoniacal thiosulfate. (C) 2021 Elsevier Ltd. All rights reserved.