Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP)
Abstract
:1. Introduction
- (i)
- Catalytic effect of pyrite on thiosulfate decomposition. The catalyzed decomposition of thiosulfate by pyrite has been reported by a number of researchers [8,23,28,29,30,31]. It is believed that the strong affinity of pyrite for aqueous sulfur species and the semiconducting properties of pyrite lead to the catalysis of pyrite in the degradation of thiosulfate in aqueous solutions of pH 2.9–8.6 [29]. An interfacial intermediate complex was considered to be formed by pyrite, thiosulfate and oxygen, of which thiosulfate is the aqueous electron donor on anodic sites and oxygen is the terminal electron acceptor on cathodic sites [24,29].
- (ii)
- Dissolution behavior of pyrite. It has been shown that iron-containing sulfide minerals such as pyrite, pyrrhotite, arsenopyrite, and chalcopyrite can be partially dissolved in ammoniacal thiosulfate liquors [8,28]. During the dissolution of pyrite, copper(II) and oxygen were found to be consumed and simultaneously a lower slurry potential was caused [24]. Scanning Electron Microscopy (SEM), Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS) analyses indicated that the leaching of pyrite largely took place at high-energy crystal boundaries and defect sites whilst iron oxide (hematite) was found to be formed at the pyrite surface after leaching [23,28].
- (iii)
- Gold adsorption and precipitation on pyrite surfaces. In thiosulfate-deficient solutions, dissolved gold can adsorb and precipitate on sulfide minerals, resulting in a lower gold recovery. The adsorption and precipitation of gold as the metal tended to occur at defect sites on the surface of sulfide mineral [31,32,33,34]. It was reported that gold precipitated on pyrite was difficult to be recovered unless undergoing the treatment with cyanide [31].
- (iv)
- Passivation of gold by iron species coating on gold surfaces. In the presence of pyrite, some iron-containing species can also be formed and may be responsible for the reduced dissolution of gold due to the surface passivation. The likely passivating products were iron hydroxides/oxides such as FeO·OH, Fe2O3 or Fe2O3·nH2O [8,23,24,28].
2. Experimental Section
2.1. Minerals and Reagents
2.2. Preparation of Ammonium Alcohol Polyvinyl Phosphate (AAPP)
2.3. Leaching Experiments
2.4. Analytical Methods
3. Results
3.1. Thermodynamic Analysis
4 Cu(S2O3)35− + 8 NH3 + 4 H+ (ΔGo = −616.1 kcal/mol)
3.2. Effect of Pyrite on Thiosulfate Leaching of Gold
3.2.1. Effect of Pyrite on Thiosulfate Decomposition
3.2.2. Effect of Pyrite on Gold Dissolution
3.3. Role of AAPP Additive
3.3.1. Role of AAPP in Thiosulfate Decomposition
3.3.2. Role of AAPP in Gold Dissolution
4. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
Appendix A
Species | ΔGo298/ (kcal/mol) | Species | ΔGo298/ (kcal/mol) | Species | ΔGo298/ (kcal/mol) | Species | ΔGo298/ (kcal/mol) |
---|---|---|---|---|---|---|---|
Fe | 0 | Fe(OH)O(aq) | −105.700 | Cu(NH3)42+(aq) | −28.011 | H2S(aq) | −6.607 |
Fe0.877S | −25.533 | HFeO2(aq) | −105.700 | Cu(NH3)52+(aq) | −33.759 | HS−(aq) | 2.973 |
FeS | −24.369 | HFeO2−(aq) | −95.353 | Cu(NH3)+(aq) | −2.516 | HSO3−(aq) | −126.103 |
FeS2 | −38.247 | Fe(NH3)2+(aq) | −30.159 | Cu(NH3)2+(aq) | −15.614 | HSO4−(aq) | −180.524 |
Fe2S3 | −67.03 | Fe(NH3)22+(aq) | −37.625 | Cu(S2O3)−(aq) | −126.885 | HS2O3−(aq) | −127.183 |
FeO | −58.729 | Fe(NH3)42+(aq) | −52.421 | Cu(S2O3)23−(aq) | −254.368 | HS2O4−(aq) | −146.862 |
Fe2O3 | −177.114 | Fe(S2O3)+(aq) | −131.632 | Cu(S2O3)35−(aq) | −381.404 | S2−(aq) | 20.548 |
Fe3O4 | −241.956 | Fe(S2O3)(aq) | −147.928 | CuO22−(aq) | −41.220 | S22−(aq) | 19.055 |
Fe(OH)2 | −117.578 | Cu | 0.000 | Cu(OH)+(aq) | −30.210 | S32−(aq) | 17.657 |
Fe(OH)3 | −168.638 | CuS | −13.530 | Cu(OH)3−(aq) | −119.865 | S42−(aq) | 16.589 |
Fe2O3·H2O | 5.776 | Cu2S | −20.607 | Cu(OH)42−(aq) | −156.970 | S52−(aq) | 15.821 |
FeO·OH | −116.928 | CuO | −30.387 | Cu2(OH)3+(aq) | −16.424 | S62−(aq) | 15.827 |
Fe3+(aq) | −4.107 | Cu2O | −35.335 | Cu2(OH)22+(aq) | −67.825 | SO32−(aq) | −116.287 |
Fe2+(aq) | −21.875 | CuO·Fe2O3 | −205.969 | Cu3(OH)42+(aq) | −151.420 | SO42−(aq) | −177.907 |
FeO(aq) | −50.715 | Cu2O·Fe2O3 | −220.015 | Cu(OH)O−(aq) | −60.096 | S2O32−(aq) | −124.825 |
FeO+(aq) | −53.093 | Cu(OH)2 | −85.262 | H+(aq) | 0 | S2O42−(aq) | −143.539 |
FeO2−(aq) | −92.642 | Cu2+(aq) | 15.545 | O2(aq) | 3.899 | S2O62−(aq) | −231.605 |
FeOH2+(aq) | −57.830 | Cu+(aq) | 11.946 | H2O(aq) | −56.678 | S2O82−(aq) | −266.46 |
FeOH+(aq) | −65.845 | Cu(NH3)2+(aq) | 3.400 | NH3(aq) | −6.375 | S3O62−(aq) | −228.815 |
Fe(OH)2+(aq) | −108.077 | Cu(NH3)22+(aq) | −7.979 | NH4+(aq) | −18.977 | S4O62−(aq) | −248.627 |
Fe2(OH)24+(aq) | −111.743 | Cu(NH3)32+(aq) | −18.500 | S | 0 | S5O62−(aq) | −228.331 |
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Liu, X.; Xu, B.; Min, X.; Li, Q.; Yang, Y.; Jiang, T.; He, Y.; Zhang, X. Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP). Metals 2017, 7, 278. https://doi.org/10.3390/met7070278
Liu X, Xu B, Min X, Li Q, Yang Y, Jiang T, He Y, Zhang X. Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP). Metals. 2017; 7(7):278. https://doi.org/10.3390/met7070278
Chicago/Turabian StyleLiu, Xiaoliang, Bin Xu, Xin Min, Qian Li, Yongbin Yang, Tao Jiang, Yinghe He, and Xi Zhang. 2017. "Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP)" Metals 7, no. 7: 278. https://doi.org/10.3390/met7070278