Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Investigating the effects of selenium and thiourea concentration on copper electrowinning
Thesis (MEng)--Stellenbosch University, 2016.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | en_ZA |
| Published: |
Stellenbosch : Stellenbosch University
2016
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867614141180542976 |
|---|---|
| access_status_str | Open Access |
| author | Ngandu, Franklin |
| author2 | Dorfling, Christie |
| author_browse | Dorfling, Christie Ngandu, Franklin |
| author_facet | Dorfling, Christie Ngandu, Franklin |
| author_sort | Ngandu, Franklin |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2016. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/100291 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:47:19.123Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/100291 Investigating the effects of selenium and thiourea concentration on copper electrowinning Ngandu, Franklin Dorfling, Christie Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. Selenium removal UCTD Thiourea Tellurium Copper ions Thesis (MEng)--Stellenbosch University, 2016. ENGLISH ABSTRACT: Recent studies have investigated different process routes for selenium and tellurium removal and recovery of platinum group metals (PGM) from copper sulphate leach solutions. The aforementioned studies have found that a substantial improvement in PGM recovery is achievable using excess thiourea as a precipitation agent instead of sulphurous acid, which is widely used at present. The current study was necessitated by the need to fully elucidate the effects that excess thiourea amounts as well as variations in selenium concentration may have on copper electrowinning efficiency and cathode quality. The experimental work was divided into electrochemical and electrowinning tests. The electrochemical tests were performed utilising a cyclic voltammetry technique to gain initial information on the possible interaction between selenium and thiourea and the copper ions during deposition. The effects of varying selenium and thiourea concentration on cathode quality and electrowinning efficiency were effectively studied by performing electrowinning tests. Both the electrowinning and electrochemical tests were conducted using a 3 electrode system consisting of a rotating disk platinum working electrode, a saturated calomel reference electrode and a graphite counter electrode. A synthetic copper sulphate electrolyte containing about 63 g/ℓ copper, 33 g/ℓ nickel, 1.2 g/ℓ iron and 35 g/ℓ sulphuric acid into which varying concentrations of selenium and thiourea had been added was used. Thiourea was investigated at levels of 10 mg/ℓ, 100 %, 200 % and 320 % excess while selenium was investigated at concentrations of 20, 57 and 150 mg/ℓ. It was observed through cyclic voltammetry that thiourea inhibited the cathodic reduction of copper ions. In the presence of excess thiourea the area under the cupric ion reduction peak decreased and shifted towards more negative values. This, coupled with a reduction in the size of the oxidation peak, indicated that thiourea polarised the working electrode and thus reduced the efficiency of the cupric ion reduction reaction. In the presence of selenium a second cathodic peak was observed. This peak was ascribed to the simultaneous reduction of copper and selenium leading to the formation of a copper selenide compound. The electrowinning tests performed in the presence of excess thiourea showed a decrease in the cathodic current and a subsequent reduction in the current density. The electrodeposits obtained in the presence of thiourea showed varying characteristics. At 10 mg/ℓ a smooth, fine grained and coherent electrodeposit was obtained. At 100 % excess thiourea a coherent but rough electrodeposit was obtained. At higher concentrations of 200 % and 320 % excess thiourea, brittle and flaky deposits were obtained. The electrodeposits were also contaminated with carbon, sulphur and nitrogen which are the constituent elements of thiourea. In the absence of thiourea a current efficiency of 96.06 % was obtained. The introduction of 10 mg/ℓ thiourea resulted into a current efficiency of 96.01 %. In the presence of excess thiourea, the current efficiencies dropped to 93.88 %, 92.87 % and 87.46 % for 100 %, 200 % and 320 % excess thiourea, respectively. The electrodeposits obtained from selenium containing electrolytes formed nodules on the surface. These deposits were also contaminated with selenium and were covered by a black mass on the surface. This black mass was ascribed to a copper selenide compound formed through the simultaneous reduction of copper and selenium. The intensity of this black mass increased with increasing selenium concentration. The presence of selenium in the electrolyte also affected the electrowinning efficiency negatively. At 20 mg/ℓ the current efficiency obtained was 95.96 % compared to 96.06 % in the absence of selenium. The current efficiency was observed to drop further to 94.78 % and 85.35 % at concentrations of 57 and 150 mg/ℓ, respectively. Based on these results, it can be concluded that precipitation of PGM from the copper sulphate solution with excess thiourea prior to electrowinning is not a feasible process option. AFRIKAANSE OPSOMMING: Onlangse studies het verskillende prosesroetes vir die verwydering van selenium en tellurium en die herwinning van platinum groep metale (PGM) uit kopersulfaat logingsoplossings ondersoek. Hierdie studies het bevind dat ʼn beduidende verbetering in PGM herwinning haalbaar is indien oormaat hoeveelhede tio-ureum as presipitasiemiddel gebruik word in plaas van swaweligsuur, wat tans algemeen gebruik word. Die huidige studie was belangrik om die effek van oormaat hoeveelhede tio-ureum sowel as variasie in die selenium konsentrasie op die koper elektrowinning effektiwiteit en katode kwaliteit te verduidelik. Die eksperimentele werk is verdeel in elektrochemiese en elektrowinning toetse. Die elektrochemiese toetse is uitgevoer deur gebruik te maak van ʼn sikliese voltammetrie tegniek om inligting te bekom oor moontlike interaksies tussen selenium en tio-ureum en die koper ione tydens deposisie. Die effek van variërende selenium en tio-ureum konsentrasie op katode kwaliteit en elektrowinning effektiwiteit is ondersoek deur elektrowinning toetse uit te voer. Beide die elektrowinning en die elektrochemiese toetse is uitgevoer deur gebruik te maak van ʼn 3-elektrode sisteem bestaande uit ʼn roterende skyf platinum werkende elektrode, ʼn versadigde kalomel verwysingselektrode en ʼn grafiet teenelektrode. ʼn Sintetiese kopersulfaat elektroliet wat 63 g/ℓ Cu, 33 g/ℓ nikkel, 1.2 g/ℓ yster en 35 g/ℓ swawelsuur sowel as variërende konsentrasies selenium en tio-ureum bevat het, is gebruik. Tio-ureum is ondersoek by vlakke van 10 dele per miljoen (dpm), 100 %, 200 % en 320 % oormaat, terwyl selenium ondersoek is by konsentrasies van 20, 57 en 150 dpm. Sikliese voltammetrie het aangetoon dat tio-ureum die katodiese reduksie van koper ione onderdruk. In die teenwoordigheid van oormaat hoeveelhede tio-ureum het die area onder die koper(II) ioon reduksie piek afgeneem en in die rigting van meer negatiewe waardes geskuif. Hierdie waarnemings, tesame met die afname in die grootte van die oksidasie piek, het aangedui dat tio-ureum die werkende elektrode gepolariseer het en dus die effektiwiteit van die koper(II) ioon reduksie reaksie verlaag het. In die teenwoordigheid van selenium is ʼn tweede katodiese piek waargeneem. Hierdie piek is toegeskryf aan die gelyktydige reduksie van koper en selenium wat aanleiding gegee het tot die vorming van ʼn koperselenied verbinding. Die elektrowinning toetse wat in die teenwoordigheid van oormaat tio-ureum uitgevoer is het ʼn afname in die katodiese stroom en ʼn gevolglike afname in die stroomdigtheid getoon. Die neerslae wat in die teenwoordigheid van tio-ureum verkry is het variërende eienskappe getoon. ʼn Gladde, koherente neerslag met ʼn fyn grein is by 10 dpm tio-ureum verkry. By 100 % oormaat tio-ureum is ʼn koherente maar rowwe neerslag verkry. Bros en skilferige neerslae is by hoër konsentrasies van 200 % en 320 % oormaat tio-ureum verkry. Die neerslae was ook besmet met koolstof, swawel en stikstof, wat die samestellende elemente van tio-ureum is. In die afwesigheid van tio-ureum is ʼn stroom effektiwiteit van 96.06 % behaal. Die byvoeging van 10 dpm tio-ureum het tot ʼn stroom effektiwiteit van 96.01 % aanleiding gegee. In die teenwoordigheid van ʼn oormaat tio-ureum het die stroom effektiwiteite tot 93.88 %, 92.87 % en 87.46 % vir 100 %, 200 % en 320 % oormaat tio-ureum, onderskeidelik, geval. Die neerslae wat verkry is vanaf selenium bevattende elektroliete het knoppies op die oppervlak gevorm. Hierdie neerslae was ook besmet met selenium en was bedek met ʼn swart massa op die oppervlak. Die swart massa is toegeskryf aan ʼn koperselenied verbinding wat gevorm het deur die gelyktydige reduksie van koper en selenium. Die intensiteit van die swart massa het toegeneem met toenemende selenium konsentrasie. Die teenwoordigheid van selenium in die elektroliet het ook die elektrowinning effektiwiteit negatief beïnvloed. ʼn Stroom effektiwiteit van 95.96 % is behaal by 20 dpm in vergelyking met 96.06 % in die afwesigheid van selenium. Die stroom effektiwiteit het verder afgeneem na 94.78 % en 85.35 % by konsentrasies van 57 en 150 dpm, onderskeidelik. Gebaseer op hierdie resultate kan die gevolgtrekking gemaak word dat dit nie lewensvatbaar is om PGM met oormaat tio-ureum vanuit die kopersulfaat oplossing te presipiteer voor koper elektrowinning nie. Masters 2016-12-22T13:36:51Z 2016-12-22T13:36:51Z 2016-12 Thesis http://hdl.handle.net/10019.1/100291 en_ZA Stellenbosch University 156 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Selenium removal UCTD Thiourea Tellurium Copper ions Ngandu, Franklin Investigating the effects of selenium and thiourea concentration on copper electrowinning |
| title | Investigating the effects of selenium and thiourea concentration on copper electrowinning |
| title_full | Investigating the effects of selenium and thiourea concentration on copper electrowinning |
| title_fullStr | Investigating the effects of selenium and thiourea concentration on copper electrowinning |
| title_full_unstemmed | Investigating the effects of selenium and thiourea concentration on copper electrowinning |
| title_short | Investigating the effects of selenium and thiourea concentration on copper electrowinning |
| title_sort | investigating the effects of selenium and thiourea concentration on copper electrowinning |
| topic | Selenium removal UCTD Thiourea Tellurium Copper ions |
| url | http://hdl.handle.net/10019.1/100291 |
| work_keys_str_mv | AT ngandufranklin investigatingtheeffectsofseleniumandthioureaconcentrationoncopperelectrowinning |