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Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon
Kozuchowski, K. A. 2025. Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/73275252-e111-4fbd-8efd-ae55d4ce28ab
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613920020135936 |
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| access_status_str | Open Access |
| author | Kozuchowski, Klaudia Anna |
| author2 | Tadie, Margreth |
| author_browse | Kozuchowski, Klaudia Anna Tadie, Margreth |
| author_facet | Tadie, Margreth Kozuchowski, Klaudia Anna |
| author_sort | Kozuchowski, Klaudia Anna |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Kozuchowski, K. A. 2025. Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/73275252-e111-4fbd-8efd-ae55d4ce28ab |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132603 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:43:48.089Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132603 Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon Kozuchowski, Klaudia Anna Tadie, Margreth Akdogan, Guven Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Extraction (Chemistry) Carbon, Activated Precious metals -- Metallurgy Glycine UCTD Kozuchowski, K. A. 2025. Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/73275252-e111-4fbd-8efd-ae55d4ce28ab Thesis (MEng)--Stellenbosch University, 2025. ENGLISH ABSTRACT: Cyanidation is the commonly used procedure for precious metal extraction, however due to its toxic nature, other ‘green’ alternative are required to promote more sustainable mining operations. Amino acid, primarily glycine, has been proven to be a suitable alternative to cyanide and beneficially allows for benign operations due to its biodegradable and environmentally friendly nature. The present study investigates the extraction of gold, silver and their alloys from alkaline glycine solutions by means of granular activated carbon adsorption. The study investigates the applicability of granular activated carbon as a suitable adsorbent to extract precious metals from glycine solutions. Batch adsorption experiments were carried out under varying conditions, including solution pH (pH 10 and 12), initial metal (1 mg/L and 4 mg/L) and sorbent (4 g/L – 12 g/L) concentrations, as well as free glycine ion concentrations to analyse the effects these variables impose on the overall adsorption process to distinguish the best operating conditions that maximised metal adsorption recovery, rate and equilibrium loading capacities. A two-level full factorial design was utilised in the study to investigate the significant variable effects of three metal systems: gold-glycinate, silver-glycinate, and 50% gold – 50% silver alloy glycinate. The initial 72-hour adsorption tests indicated rapid adsorption for the gold, silver and their 50:50 wt% mixture systems, with gold reaching equilibrium within less than 6 hours and silver within less than 24 hours. Mathematical models were used to analyse the adsorption isotherms and kinetics as these elucidate the possible mechanism governing the adsorption process and provide an analysis on the subsequent variable effects and equilibrium metal loading behaviours. The adsorption isotherms were modelled using the Langmuir and Freundlich Isotherm models, and the latter was found to have better correlation to all the systems and was used as the main isotherm throughout the study. The isotherms were constructed by contacting the prepared pregnant leach solution with five different weights of sorbent (concentrations ranged from 4 – 12 g/L) in a 250mL solution for a 24-hour adsorption period. Each solution had either 1 mg/L or 4 mg/L of initial metal concentration and operated at solution pH of 10 or 12. Overall, the solution pH appeared to have an insignificant effect on the carbon loadings for each experimental conditions, but an increase in initial metal concentrations increased the carbon loadings. Carbon loading capacities for gold and silver of 7 926 mgAu/kgCarbon and 5 139 mgAg/kgCarbon for the single component were obtained under the conditions tested, and loadings for the gold and silver in the binary mixture systems of 8 118 mgAu/kgCarbon and 1 665 mgAg/kgCarbon were estimated which were within the limits of typical cyanide operating plants. In terms of the kinetics, the study was conducted through using diffusion and reaction rate models to determine which mechanisms controlled the adsorption process. The pseudo-second order rate equation was found to have the highest correlation to the systems (R2 > 0.99), thereby indicating that chemisorption was the governing mechanism which involves valency forces by the sharing or exchange of electrons between the adsorbent and sorbate. Analysis of the operating parameters effects on the adsorption kinetics indicated that the solution pH had a reasonably insignificant effect on the kinetic rates, but lower pH promoted faster kinetics overall. An increase in activated carbon concentration yielded faster kinetics, which was as expected as an increase in sorbent concentration increased the number of active sites available for effective adsorption, and an increase in initial metal concentration appeared to cause a decrease in the kinetics due to causing the sorbent to become saturated and hindering further adsorption from occurring. The free glycine ion effects were analysed through Ultraviolet spectroscopy (UV-vis) and negligible change in the glycine concentration was seen, thereby indicating the glycine had no significant effect on the overall adsorption performance. The distribution coefficient was evaluated for the alloy system to analyse the competitive adsorptive nature of the binary metal system. It was found that the gold had a higher distribution coefficient than the silver, hence showcasing that gold had a higher affinity to activated carbon than silver. A desirability function analysis (DFA) was conducted to validate which operating conditions provided optimal/maximised results based on the actual recoveries and kinetic rates. It was found that for both the single component systems and binary systems the overall best operating conditions that promoted fast and efficient adsorption performance were the systems operating at the lower solution pH of 10 and higher sorbent concentrations of 12 g/L. The study overall proved that granular activated carbon is a suitable sorbent for gold and silver extraction from glycine systems and beneficially allows for ease of integration into existing infrastructure. The study also emphasised on the idea of sustainable mining with the use of glycine as the investigation proved that glycine is able to operate as effectively as cyanide in the adsorption stage and paves the way as a potential route for sustainable mining operations. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Masters 2025-06-11T12:41:19Z 2025-06-11T12:41:19Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132603 Stellenbosch University xvii, 210 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Extraction (Chemistry) Carbon, Activated Precious metals -- Metallurgy Glycine UCTD Kozuchowski, Klaudia Anna Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon |
| title | Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon |
| title_full | Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon |
| title_fullStr | Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon |
| title_full_unstemmed | Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon |
| title_short | Extraction of gold, silver and their alloy from glycine solutions by adsorption onto granular activated carbon |
| title_sort | extraction of gold silver and their alloy from glycine solutions by adsorption onto granular activated carbon |
| topic | Extraction (Chemistry) Carbon, Activated Precious metals -- Metallurgy Glycine UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132603 |
| work_keys_str_mv | AT kozuchowskiklaudiaanna extractionofgoldsilverandtheiralloyfromglycinesolutionsbyadsorptionontogranularactivatedcarbon |