Non-Precious Group Metal Electrocatalysis of Sulfite Electro-Oxidation Reaction for Gold Electrowinning Processes
Bibliographic record
Abstract
The electro-oxidation of sulfite and its radicals has a wide range of applications from gold electrowinning to wastewater treatment, hydrogen production and in the food industry (1-4). While efforts have been made to study the electro-oxidation of sulfite ions on noble metals (e.g. Au) as well as carbon surfaces, metal oxides in general have not been thoroughly investigated for this electrochemical reaction (1, 5). During gold recovery from thiosulfate solutions, Au+ ions are reduced to Au from the thiosulphate gold complex on the cathode while oxygen evolution occurs on the anode via the following reactions (6): Au(S2O3)2 3- + e- = Au + 2S2O3 -2, E0= 0.15 V (1) 4OH- = 2H2O + O2 + 4e-, E0= 0.4 V (2) To drive the cathodic reaction, high current densities are used, which result in high anodic potentials on the stainless-steel anodes. Such high anodic potentials may cause transpassive corrosion of the anode as well as significant, and undesirable, changes in solution chemistry (7). This study systematically investigated the effect of operating factors on the corrosion behavior of stainless steel anodes in thiosulfate solutions during gold electrowinning. Further, novel non-precious group materials such as manganese oxides and perovskites were used as electrocatalysts for sulfite electro-oxidation to ultimately enhance the activity and long-term durability of the anodes in the gold electrowinning process (8). A 2n half-fraction factorial design study was performed to find the effect of five important parameters involved in the gold electrowinning process (i.e. thiosulfate concentration, sulfite concentration, sulfate concentration, temperature and applied anodic current density), on the anodic potential of the stainless steel anode. As shown in the Fig. 1A, increasing the sulfite concentration and temperature of the gold electrowinning solution lead to a low anodic potential of 550 mV which is about 250 mV lower than the transpassive corrosion potential for the 316 stainless steel anodes. To further reduce the anodic potential and employ the high sulfite concentration (i.e. 3000-32000 ppm) in the gold electrowinning solution, non-precious metal oxides were tested to facilitate the electrowinning process by catalyzing the following sulfite electro-oxidation reaction instead of the oxygen evolution reaction (eq. 2): SO3 2- + 2OH- = SO4 2- + H2O + 2e-, E0= -0.93 V (3) Fig. 1B shows that a combination of manganese oxide and perovskite electrocatalysts provides promising electrocatalytic activity and durability for sulfite electro-oxidation (i.e. up to 500 mV lower onset-potential over 7 hours of testing at 3.5 mAcm-2) compared to the Ni, commercial Ag/AgO, Pt, carbon, commercial Pb-2 wt% Ag and stainless steel electrodes tested here. Fig. 1 A) Surface plot produced from the 2n half-fraction factorial design study on the effect of five electrowinning parameters on the performance of 316 stainless steel gold electrowinning anode. B) A comparison between the electrocatalytic activity of various electrocatalyst materials for sulfite electro-oxidation in a solution of 100 ppm NaCl + 3000 ppm Na2SO4 + 32000 ppm Na2SO3 at 3.5 mA cm-2 and 45 °C. All MnO2-based catalysts are under the license with Catalyst Square Materials Ltd (8). References: P. Westbroek, J. De Strycker, K. Van Uytfanghe and E. Temmerman, Journal of Electroanalytical Chemistry, 516, 83 (2001). J. A. Allen, G. Rowe, J. T. Hinkley and S. W. Donne, International Journal of Hydrogen Energy, 39, 11376 (2014). R. Ojani, J. B. Raoof and A. Alinezhad, Electroanalysis, 14, 1197 (2002). E. M. Contreras, Industrial & Engineering Chemistry Research, 47, 9709 (2008). A. G. Zelinsky and B. Y. Pirogov, Electrochimica Acta, 231, 371 (2017). C. Abbruzzese, P. Fornari, R. Massidda, F. Vegliò and S. Ubaldini, Hydrometallurgy, 39, 265 (1995). N. J. Laycock, R. C. Newman and J. Stewart, Corrosion Science, 37, 1637 (1995). E. Gyenge and P. Hosseini-Benhangi, An oxygen electrode and a method of manufacturing the same, in, U.S. (15/251,267) and Canadian (2,940,921) patent applications (Filed on August 30, 2016). Figure 1
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".