Effect of varying operating conditions on cathode surface roughness using guar as a smoothing agent in copper electrowinning
| dc.contributor.advisor | Tadie, Margreth | en_ZA |
| dc.contributor.advisor | Dorfling, Christie | en_ZA |
| dc.contributor.author | Mkhawana, Nhlamulo | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. | en_ZA |
| dc.date.accessioned | 2021-12-06T10:57:37Z | |
| dc.date.accessioned | 2021-12-22T14:30:04Z | |
| dc.date.available | 2021-12-06T10:57:37Z | |
| dc.date.available | 2021-12-22T14:30:04Z | |
| dc.date.issued | 2021-12 | |
| dc.description | Thesis (MEng)--Stellenbosch University, 2021. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Organic additives play a very important role in copper electrowinning to facilitate the production of cathode deposits with improved morphology. Guar has been used as the standard organic additive in copper electrowinning (EW) because of its compatibility with solvent extraction (SX) stage, as well as its ability to eliminate dendrite growth on the cathode surface. Dendrite formation produces an undesirable rough cathode surface, and a loss in current efficiency can be expected due to short circuits resulting from dendrite growth. In tankhouses, guar is dosed continuously since its performance reduces as it degrades by hydrolysis under acidic conditions. This project investigated the interaction of guar dosage with other electrowinning operating parameters and their effect on current efficiency and deposit quality. A bench scale electrowinning cell was used to conduct 24-hour electrowinning experiments by employing a mixed level factorial experimental design to investigate the interaction of guar dosage (2, 10 and 18 mg/l) with copper (35 and 45 g/l), sulphuric acid (150 and 180 g/l) and current density (180 and 300 A/m2) at a temperature of 40oC and their effect on the measured responses (current efficiency and cathode deposit quality). The electrolyte used was free of impurities with the addition of 25 mg/l chloride to act as de-polarizer and grain refiner in the copper deposition process. The mean surface deviation (Sa) value, which is a measure of surface roughness, was calculated for each copper plate produced. Acid digestion tests using aqua regia were conducted for 24 hours to investigate the chemical composition for all the copper plates. The amount of sulphur in the dissolved copper plates was analysed using the ICP analysis technique. A statistical analysis was performed to analyse the deposited surface roughness, current efficiency, and sulphur content. The electrowinning results showed an improvement in the elimination of dendrites, producing a smoother copper deposit in the presence of guar than a deposit achieved in the absence of guar in the electrolyte. The calculated Sa values and interaction plots shows that the individual and interactive effects of the operating parameters on the surface roughness in the presence of guar are dependent on the experimental conditions. The copper deposit achieved at 300 A/m2 current density, 45 g/l initial copper concentration, 180 g/l sulphuric acid concentration and 18 mg/l guar concentration had the lowest calculated Sa value (30.95 μm) and arguably the smoothest, brightest of all the deposits. Current density was observed to be the most influential parameter affecting the roughness of copper deposits while guar has an insignificant effect as predicted by statistical analysis. The interaction plots suggest that higher guar concentrations (10 mg/l or 18 mg/l) are more effective in reducing surface roughness than 2 mg/l guar concentration. Current efficiency (CE) values calculated for each experiment were high (98-99%) and varied by less than 1%. The little variance shows that varying guar concentrations had a minor impact on the CE for various operating conditions. Current density is the only influential parameter affecting current efficiency as predicted by statistical analysis. The chemical composition results show that the sulphur content in copper deposits increases at high guar concentrations and low current density. It was suggested that sulphate ions may be the source of sulphur entrapped in copper deposits. Statistical analysis of sulphur on each copper plate produced shows that current density and guar concentration significantly influences the amount of sulphur content. This study provides an industrially informed baseline against which new organic additives can be compared. Based on electrowinning experiments and statistical analysis results, it can be concluded that the adjustment of operating parameters in conjunction with an effective smoothing agent can reduce short-circuiting in copper electrowinning. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Organiese bymiddels speel ’n baie belangrike rol in koperelektroherwinning om die produksie van katodeneersettings met verbeterde morfologie te fasiliteer. Guar is gebruik as die standaard organiese bymiddel in koperelektroherwinning vanweë guar se versoenbaarheid met die oplosmiddelekstraksie (SX) stadium, sowel as guar se vermoë om dendriete se groei op die katode-oppervlak te elimineer. Dendrietformasie produseer ’n ongewenste growwe katode-oppervlak en ’n verlies aan stroomdoeltreffendheid kan verwag word as gevolg van kortsluitings wat volg uit dendrietgroei. In tenkhuise word guar aanhoudend gedoseer aangesien sy doeltreffendheid verlaag soos dit degradeer deur hidrolise onder suur kondisies. Hierdie projek het die interaksie van guar dosering met ander koperelektroherwinning bedryfsparameters en hul effek op stroomdoeltreffendheid en katodeneerslagkwaliteit ondersoek. n Banktoetsskaalelektroherwinningsel is gebruik om 24-uur elektroherwinningeksperimente uit te voer deur ’n gemengde vlak faktoriaal eksperimentele ontwerp te gebruik om die interaksie van guardosis (2, 10 en 18 mg/l) met koper (35 en 45 g/l), swaelsuur (150 en 180 g/l) en stroomdigtheid (180 en 300 A/m2) te ondersoek by ʼn temperatuur van 40°C, en hul effek op die gemete response (stroomdoeltreffendheid en katodeneerslagkwaliteit). Die elektroliet wat gebruik is, het geen onsuiwerhede gehad nie, met die byvoeging van 25 mg/l chloried om as de-polariseerder en graanraffineerder op te tree in die koperneerslagproses. Die gemiddelde oppervlakafwyking (Sa)- waarde, wat ’n mate van oppervlakgrofheid is, is bereken vir elke koperplaat wat geproduseer is. Suurverteringtoetse wat koningswater gebruik het, is vir 24 uur uitgevoer om die chemiese samestelling vir al die koperplate te ondersoek. Die hoeveelheid swael in die opgeloste koperplate is geanaliseer deur die ICP-analisetegniek te gebruik. ’n Statistiese analise is uitgevoer om die neerslagoppervlakgrofheid, stroomdoeltreffendheid, en swaelinhoud te analiseer. Die elektroherwinningresultate het ’n verbetering in die eliminasie van dendriete getoon wat ’n gladder koperneerslag in die teenwoordigheid van guar produseer, teenoor dié geproduseer in die afwesigheid van guar in die elektroliet. Die berekende Sa-waardes en interaksieplotte wys dat die individuele en interaktiewe effek van die bedryfsparameters op die oppervlakgrofheid in die teenwoordigheid van guar afhanklik is van die eksperimentele kondisies. Die koperneerslag bereik by 300 A/m2 stroomdigtheid, 45 g/l aanvanklike koperkonsentrasie, 180 g/l swaelsuurkonsentrasie en 18 mg/l guarkonsentrasie het die laagste berekende Sa-waarde (30.95 μm) en is besmoontlik die gladste, helderste van al die neerslae. Stroomdigtheid is waargeneem om die mees invloedryke parameter te wees wat die grofheid van koperneerslae affekteer terwyl guar ’n onbeduidende effek gehad het, soos voorspel deur statistiese analise. Die interaksieplotte stel voor dat hoër guarkonsentrasies (10 mg/l of 18 mg/l) meer effektief is in die vermindering van oppervlakgrofheid as 2 mg/l guarkonsentrasie. Stroomdoeltreffendheid (CE)-waardes bereken vir elke eksperiment was hoog (98 – 99%) en het met minder as 1% gevarieer. Die bietjie variansie het gewys dat verskeidenheid guarkonsentrasies minimale impak op die CE vir verskeie bedryfskondisies het. Stroomdigtheid is die enigste invloedryke parameter wat stroomdoeltreffendheid affekteer soos voorspel deur statistiese analise. Die chemiese samestelling se resultate toon dat die swaelinhoud in koperneerslae verhoog by hoër guarkonsentrasies en lae stroomdigtheid. Dit is voorgestel dat sulfaatione moontlik die bron is van swael wat vassit in koperneerslae. Statistiese analise van swael op elke koperplaat geproduseer, het getoon dat stroomdigtheid en guarkonsentrasie beduidende invloed het op die swaelinhoud. Hierdie studie verskaf ’n industriële ingeligte basislyn waarteen nuwe organiese bymiddels opgeweeg kan word. Gebaseer op elektroherwinningeksperimente en statistiese resultate kan dit beslis word dat die verstelling van bedryfsparameters in samewerking met ’n doeltreffende gladmakingsbymiddel kortsluiting in koperelektroherwinning kan verminder. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.format.extent | 151 pages | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/123935 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Guar | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.subject | Electrowinning | en_ZA |
| dc.subject | Copper | en_ZA |
| dc.subject | Surface roughness | en_ZA |
| dc.subject | Statistical analysis | en_ZA |
| dc.title | Effect of varying operating conditions on cathode surface roughness using guar as a smoothing agent in copper electrowinning | en_ZA |
| dc.type | Thesis | en_ZA |