This article contains the results of experiments to recover gold from complex mineral raw materials containing more than 15 % arsenic. Laboratory tests showed that standard cyanidation recovers only 26,4 % of gold into the solution. Additional oxidizing reagents used increase the leaching efficiency and enable to recover more than 40 % of gold during subsequent cyanidation. The efficiency has been established for replacement of cyanide with thiourea and thiosulfate solutions. 79,5 %, i.e. the maximum recovery rate, was found in the experiment with preliminary oxidation with T. Ferrooxidans, a bacterial culture, followed by leaching with a thiourea solution

A. K. Koizhanova

A. N. Berkinbayeva

B. K. Kenzhaliyev

D. R. Magomedov

G. V. Sedelnikova

M. N. Azlan

Y. M. Efremova (Dyo)

English

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423METALURGIJA 60 (2021) 3-4, 423-426A. K. KOIZHANOVA, A. N. BERKINBAYEVA, G. V. SEDELNIKOVA, B. K. KENZHALIYEV,  M. N. AZLAN, D. R. MAGOMEDOV,Y. M. EFREMOVA (DYO)RESEARCH OF BIOCHEMICAL GOLD RECOVERY METHOD USING HIGH-ARSENIC RAW MATERIALSReceived – Primljeno: 2020-12-02Accepted – Prihvaćeno: 2021-03-20Preliminary Note – Prethodno priopćenjeA. K. Koizhanova (a.koizhanova@satbayev.university) Satbayev Uni-versity, JSC “Institute of Metallurgy and Ore Beneficiation”, Almaty, Republic of KazakhstanG. V. Sedelnikova (gsedelnikova@mail.ru) JSC «Rosgeologia» Moscow, Russian FederationM. N. Azlan (azlanmn@smt.upsi.edu.my) Physics Department, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, Tan-jung Malim, Perak, Malaysia A. N. Berkinbayeva,  B.K. Kenzhaliyev,  D.R. Magomedov, Y. M. Efremova (Dyo), Satbayev University, JSC “Institute of Metal-lurgy and Ore Beneficiation”, Almaty, Republic of KazakhstanThis article contains the results of experiments to recover gold from complex mineral raw materials containing more than 15 % arsenic. Laboratory tests showed that standard cyanidation recovers only 26,4 % of gold into the solution. Additional oxidizing reagents used increase the leaching efficiency and enable to recover more than 40 % of gold during subsequent cyanidation. The efficiency has been established for replacement of cyanide with thiourea and thiosulfate solutions. 79,5 %, i.e. the maximum recovery rate, was found in the experiment with preliminary oxida-tion with T. Ferrooxidans, a bacterial culture, followed by leaching with a thiourea solution. Keywords: hydrometallurgy, biochemical method, arsenic, gold, recoveryINTRODUCTIONAt present, bacterial leaching is widely used in some countries with the purpose to produce other metals commercially from ores. Intensive biohydrometallurgy studies enable to involve huge reserves of non-commer-cial and waste ores, as well as middlings and wastes from processing plants into processing. This method is cost-effective, reduces environmental pollution and provides an integrated use of mineral raw materials. Iron-oxidizing bacteria as the most commonly used class of Ferrooxidans has numerous strains that differ in both genetics and metabolic features. Therefore, the same bacterial strain cannot serve as a universal oxi-dizer for absolutely all types of raw material.That is why, it is required to breed and test iron-oxidizing bacteria strains adapted to rock mineralogy conditions, the composition of the hydrosphere and lithosphere of a particular depositto the maximum in the biochemical technology study process.The first commercialization of bacterial cultures in the field of gold hydrometallurgy dates back to 1986, when the BIOX® biooxidation technology was successfully ap-plied at the Fairview gold mine in South Africa [1].The main advantages of bacterial oxidation are the high efficiency of the ferrous iron conversion into ferric ISSN 0543-5846METABK 60(3-4) 423-426 (2021)UDC – UDK 669.22.8:577.1.16:661.64:546.59.002.2=111iron, and the low cost of this technology. The prospects and efficiency of bacterial leaching are considered in the works of domestic and foreign scientists. [2-6].Biochemical gold leaching usually combines a num-ber of different hydrometallurgical methods where the ore is pre-concentrated, then the resulting concentrate is cleaned with acid. The pulp is washed in the presence of iron (II) sulfate, then treated with a bacterial solution containing iron (II) and a culture of Thiobacillus ferroox-idans bacteria, where iron (II) is oxidized by bacteria. The oxidized pulp is cyanided after water washing [7].The study works [8] describe the pyrite and arseno-pyrite oxidation mechanism at high pressurein detail. It would requireto implement autoclave leaching that has a number of disadvantages (limited amount, high oper-ating costs, and the need to increase the control over the equipment) to use it commercially. Some works [9-10] provide a review of the arsenopyrite transformations during the oxidative attack of Acidithiobacillus Fer-rooxidans bacteria culture. The main extraction mecha-nism for gold-bearing sulfide minerals of pyrite and ar-senopyrite in all cases occurs due to the iron oxidation. The search for alternative cyanide-free leaching methods is one more important study area in modern gold hydrometallurgy. Leaching is performed in an acidic medium at pH = 2 - 4; thiourea is not oxidized under these conditions, and sulfuric acid solution of ferric salt Fe2(SО4)3 is used as an oxidizing agent. The process speed directly depends on the solution pH and the con-centrations of thiourea and iron (III) sulfate. The thiourea [CS(NH2)2] complexation capacity is determined with NH2 - C = S group present in the compound. The stability of the gold thiocarbamide complex (Au[CS(NH2)2]2+) de-termined by the polarographic method, is 4,4×1022.The cationic complex of gold, Au[CS(NH2)2]+2 formed with thiourea molecules has an instability con-424A.K. KOIZHANOVA et al.: RESEARCH OF BIOCHEMICAL GOLD RECOVERY METHOD USING HIGH-ARSENIC... METALURGIJA 60 (2021) 3-4, 423-426stant equal to 3,2 × 10-26. Therefore, the standard poten-tial of gold in a thiourea solution decreases to +0,38 V. It explains the gold solubility in acidic aqueous thiourea solutions containing Fe3+ ions as an oxidizing agent:Au+2CS(NH2)2+Fe3+=Au[CS(NH2)2]+Fe2+STUDIES AND ANALYSISThe study objects are samples of mineral raw materials taken from two sampling points ina gold ore deposit. First of all, X-ray fluorescence and chemical analyzes were per-formed to determine the chemical composition of the sam-ples. The results are presented in Tables 1 and 2.The results of Table 1 demonstrate a very high con-tent of arsenic, sulfur and iron in both samples that is typical for high content of pyrite and arsenopyrite min-erals. The chemical analysis results from Table 2 showed that the gold content in sample 1 is 4,75 g/t and in sample 2 is 5,84 g/t.X-ray phase analysis showed some differences in the composition of the samples. The analysis revealed a clear predominance of arsenopyrite (29,2 %) quartz (16,5 %) and pyrite (10,3 %) in the first sample, the rest of the mass was accounted for various aluminosilicate inclusions. The second sample turned out to be more diverse in terms of aluminosilicate and magnetite min-eral phases. The content of arsenopyrite and pyrite was 11,2 % and 6,7 %, respectively.Scanning electron microscopy has recorded spectra of sulfur, arsenic and iron next to the gold spectra points detected for the test samples that is typical for the as-sociations of gold with arsenopyrite (Figure 1).Rational phase analysis was also performed to deter-mine the form of gold in the samples. In the first sample, 82,11 % of gold is mainly bonded to mineral lattice, fine gold and visible gold in nuggets are 7,37 % each, while gold in quartz is only 3,15 %. The bulk of the precious metal is bonded to mineral lattice (76 %), gold inclusions in quartz accounts for 12 %, fine gold in nuggets accounts for 7,7 %, free nugget form is 4,3 % in the rationally phase composition of the second sample as in the first one.Research of cyanide-free leaching using oxidizing reagents. Bacterial oxidation. Experiments using di-rect cyanidation with 0,1 % sodium cyanide solution served as a reference to compare with other methods. A 70 % technical mixture of trichloroisocyanuric acid (TCCA) was used as a chlorine-containing oxidant. The application of sulfanol, a surfactant, was considered among the variants for organic oxidants.Various combinations of thiosulfate and thiourea so-lutions with the addition of oxidizing components served as alternative leaching reagents in the variants of cyanide-free gold recovery. Two applications of sodium chloride in combination with a thiosulfate solution were tested as additional chloride applications, and one ap-plication of ammonia solution was also tested in one of the applications. The efficiency of hydrogen peroxide as an oxidizing reagent in leaching with thiourea was studied besidesthe use of chlorine-containing and or-ganic oxidants in the cyanide-free leaching process.Table 1 Results of X-ray fluorescence analysis of samplessample 1Element /% Element /%О 31,675 Fe 15,109Na 0,821 Co 0,04Al 4,477 Cu 0,115Si 15,677 Zn 0,006P 0,034 As 17,15S 11,877 Rb 0,006Cl 0,048 Sr 0,007K 1,00 Zr 0,012Ca 1,71 Sb 0,027Ti 0,103 Bi 0,065sample 2Element /% Element /%O 44,097 Cr 0,018Na 0,862 Mn 0,018Al 3,669 Fe 14,602Si 12,5 Co 0,041P 0,028 Ni 0,015S 5,025 Cu 0,113Cl 0,072 As 15,627K 0,935 Rb 0,007Ca 1,26 Zr 0,016Ti 0,108 Bi 0,075Table 2 Results of chemical analysis of the samplesSample Au / g/t Ag / g/t Fe /% S /  % Cu / %sample 1 4,75 0,92 20,9 12,72 0,1sample 2 5,84 1,67 18,23 5,37 0,11Figure 1 Scanning electron microscopic (SEM) images  (a) spectra: As – 73,07 %, Fe – 15,86 %, S – 11,07 %; (b) spectra: Au- 96,41 %, Ag- 3,59 %.Figure 2  Selection and accumulation of bacterial biomass (a) Selection of a nutrient medium for the growth of an adapted culture of Th.Ferrooxidans for the test raw material; (b) General view of bacterial cells; (c) adaptation of Th.Ferrooxidans pure culture to arsenic under a microscope.425A.K. KOIZHANOVA et al.: RESEARCH OF BIOCHEMICAL GOLD RECOVERY METHOD USING HIGH-ARSENIC...METALURGIJA 60 (2021) 3-4, 423-426Previous experiments for the preliminary oxidation of a sample of mature tails with a bacterial culture showed a low adaptation of the common Ferrooxidans strain to the high content of arsenic in the composition of mineral raw materials. Due to it, a representative sample was sent to the research laboratory of Rosgeologia JSC, Moscow, for the isolation and growth of a viable strain of microorgan-isms, followed by bacterial acidification of the mineral raw material pulp (Figure 2).After the selection of the adapted strain, bacterial acidification of the sorption tailings sample was per-formed for 10 days at a ratio of S:L = 1:2 and pH = 1,5 - 2,0. After pulp oxidation, chemical analysis of the spent bacterial solution showed the presence of the following elements: iron – 0,84 g/L, copper – 25,4 mg/L, arsenic – 1,0 g/L. The arsenopyrite minerals contained in the sam-ple as a result of the oxidation reaction pass mainly into insoluble arsenates AsO43- and remain in the solid phase of the pulp, while not more than 1,5 - 2,0 % of the total arsenic content passes into the solution in the oxidation process. Microbiological analysis recorded a significant reduction in living cells in the spent bacterial solution (106 to 103 C/cm3). The oxidized pulp was used in gold leaching experiments after decantation and removal of the bacterial solution. Leaching was performed with three solutions for comparative experiments:1)  sodium cyanide solution – 1 g/L (after pH in-crease up to 10,5 - 11,0); 2) thiourea solution – 1 g/L; 3) sodium thiosulfate solution – 6,7 g/L.In total, there were 17 variants of experiments in-cluding 5 cases where sodium cyanide was used as a leaching solution for the control comparison. The con-ditions of the experiments are showed in Table 3.The results of the experiments (Table 4) showed the applicability of oxidizing reagents in the leaching gold process from refractory raw materials represented by sorption tailings. Conventional direct cyanidation con-sidered as a reference variant yields 26,4 % recovery. Besides, variants with additional oxidation of the sam-ple with hydrogen peroxide, TCCA, bacteria were con-sidered to compare the methods involving the use of cyanide as the main reagent in the gold leaching pro-cess. For example, cyanidation after using hydrogen peroxide enables to extract 40,1 % of gold and 42,3 % of TCCA, and the maximum recovery (69,5 %) was ob-served during preliminary bacterial oxidation.The use of a mixture of TCCA and hydrochloric acid in thiourea leaching enables to extract 50 % of gold. The maximum recovery rate, 79,5, was observed in the experiment with preliminary oxidation with T. Ferroox-idans, a bacterial culture adapted to high arsenic con-tent, followed by leaching with a thiourea solution.CONCLUSIONThe processing of gold-bearing raw materials with complex composition always requires additional techno-logical operations to destroy the crystal lattices of sulfide gold-bearing minerals. Preliminary bacterial oxidation methods are widely used besides the use of chemical oxidants. However, the biological oxidation method ap-plication requires a long and complex work to adapt the bacterial culture to large amounts of arsenic in the min-eral composition of the samples under study. Breeding and growing the adapted culture of Th.Ferrooxidans al-lows further efficient oxidation of mineral raw materials and gold leaching with both cyanide and alternative solu-tions. Besides, the costs of neutralizing the final effluents and leach tailings are reduced due to the replacement of cyanide with a thiourea solution.Biochemical leaching experiments assuming bacte-rial pre-oxidation showed maximum results: 69,5 % with further cyanidation and 79,5 % with thiourea leaching.Table 3  Leaching conditions for gold samples with Au content of 5,84 g/tVar.No.Leaching parameters 1 NaCN 0,1 %2 2 mL of H2O2 + 1 g of CS(NH2)24 2 mL of H2O2 + 0,5 g of CS(NH2)25 2 mL of H2O2 + 1g/L of NaCN6 16 g/L of NaCl + 6,7 g/L of Na2S2O3 + 7 g/L of NH4OH7 16 g/L of NaCl + 6,7 g/L of Na2S2O38 1,5 g of TCCA for 2 hours; 1 g/L of NaCN9 1,5 g of TCCA for 2 hours; 0,5 g of CS(NH2)210 1,5 g of TCCA for 2 hours; 6,7 g/L of Na2S2O311 6,7 g/L of Na2S2O3 + sulfanol12 1 g of CS(NH2)2 + 2 mL of HCl + sulfanol13 1 g of CS(NH2)2 + 4 mL of HCl + 0,5 g of TCCA14 1 g of CS(NH2)2 + 5 mL of HCl15 Bacteria; 1 g of NaCN 0,1%16 Bacteria; 1 g of CS(NH2)217 Bacteria; 6,7 g/L of Na2S2O3Table 4  Results of gold leaching of samples with Au content of 5,84 g/tVar.No.рН CakeAu / g/t)Е  Au / %1 10,5 4,3 26,42 2,1 3,86 33,94 2,1 3,43 41,35 11,0 3,5 40,16 9,0 3,14 46,27 3,0 3,25 44,38 1,9→10,6 3,372 42,39 2,1 4,308 26,210 3,6 4,392 24,811 2,0 3,672 37,112 1,0 4,184 28,413 1,0 2,92 50,014 1,0 3,8 34,915 2,0→11,0 1,78 69,516 2,0 1,198 79,517 2,0 3,05 47,8426A.K. KOIZHANOVA et al.: RESEARCH OF BIOCHEMICAL GOLD RECOVERY METHOD USING HIGH-ARSENIC... METALURGIJA 60 (2021) 3-4, 423-426AcknowledgmentThis work was financially supported by the Ministry of Education and Science of the Republic of Kazakh-stan within the framework of grant and program-target-ed financing of the Ministry of Education and Science of the Republic of Kazakhstan (No. AP05130143 and АР08855505).REFERENCES[1] Naboychenko S.S., Shneнerson Ya. M. et al. Autoclave hydrometallurgy of non-ferrous metals. Yekaterinburg. State Educational Institution of Higher Professional Edu-cation “Ural Federal University named after the first Presi-dent of Russia B. N. Yeltsin”. 2 (2009) 353.[2] Koizhanova A.K., Toktar G., Craig E. Banks., Magome-dov D.R., Kubaizhanov A.A. Research of hydrometallur-gical method of leaching gold from flotation tails with using bio-oxidation // Complex Use of Mineral Resources 314 (2020) 3, 28-39. https://doi.org/10.31643/2020/6445.24[3] Mongush G. R., Application of biotechnology to process mineral deposits in Tuva. Electronic scientific journal “New researches of Tuva”. 1 (2010), 228.[4] Chinmay Sen, Bioleaching of Gold: An alternative green mining technology for 21st century. Microbiology World 3 (2015) 2, 11-20.[5] Kenzhaliyev B.K., Surkova, T.Y., Berkinbayeva, A.N., Dosymbayeva Z.D., Abdikerim B.E. (2020). Revisiting the Kazakhstan natural sorbents modification. Metalurgija 59 (2020) 1, 117-120.[6] W. Yang, H. Cao, K. Zhang, G. Wang Influence of copper morphology on copper and gold leaching rates in calcine and acid leaching residue. Guocheng Gongcheng Xuebao / The Chinese Journal of Process Engineering 6 (2018), 1226-1231. doi: 10.12034/j.issn.1009-606X.218112[7] Semenchenko G.V., Mukusheva A.S. Structurally-phase transformations of pyrite in biochemical solution system. World Congress on Engineering and Technology (CET), Shanghai, China, Oct.28-Nov.2, 3 (2011), 856-859.[8] Yang Y., Chen J., Liu W., Zhong S., Ma Y., Gao X., M. Chen, The impacts of pyrite/pyrrhotite on aqueous arsenic species in arsenopyrite pressure leaching: An XAS study. Minerals Engineering 155 (2020), 1-8.  https://doi.org/10.1016/j.mineng.2020.106447[9] Wang, X., Li, Q., Liao, Q., Yan, Y., Xia, J., Lin, Q., Wang, Q., Liang, Y. Arsenic(III) biotransformation to tooeleite associated with the oxidation of Fe(II) via Acidithiobacil-lus ferrooxidans. Chemosphere 248 (2020), 1-9. https://doi.org/10.1016/j.chemosphere.2020.126080[10] Zhao, H.F., Yang, H.Y., Tong, L. Zhang, Q., Kong, Y. Biooxidation-thiosulfate leaching of refractory gold con-centrate International Journal of Minerals, Metallurgy and Materials 27 (2020) 8, 1075-1082.Note:  The responsible translator for English language is Nastya Kurash, Translation agency «ART Translations».

Research of biochemical gold recovery method using high-arsenic raw materials

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Research of biochemical gold recovery method using high-arsenic raw materials

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