Investigation of characteristics of polyacrylamide-based additives for copper electrowinning

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dc.contributor.advisorTadie, Margrethen_ZA
dc.contributor.advisorDorfling, Christieen_ZA
dc.contributor.authorMasoga, Ivoryen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Process Engineering.en_ZA
dc.date.accessioned2023-03-03T12:28:50Zen_ZA
dc.date.accessioned2023-05-18T07:18:28Zen_ZA
dc.date.available2023-03-03T12:28:50Zen_ZA
dc.date.available2023-05-18T07:18:28Zen_ZA
dc.date.issued2023-03en_ZA
dc.descriptionThesis (MEng)--Stellenbosch University, 2023.en_ZA
dc.description.abstractENGLISH ABSTRACT: The formation of nodulations during copper electrowinning remains a major operational concern because it increases the energy consumption of the operation and decreases the quality of the copper plates. Smoothing agents are introduced to mitigate the formation of nodulations and improve the efficiency of the process. One of the emerging prospects is polyacrylamides, research has shown that polyacrylamides have the potential to compete with the industry's leading additives, furthermore, it was also reported that molecular characteristics of polyacrylamides such as molecular weight can influence their grain refining efficacies i.e., reduce nodulation. This study investigated the structurally different polyacrylamide additives in terms of their viscosity in the solution and their percentage ionic charge. Their characteristics are compared in electrochemical methods and then related to electrowinning. Moreover, this study also investigated the compatibility of the additives with solvent extraction, an upstream process of copper electrowinning. This study was divided into three phases. The first phase was the fundamental study using cyclic voltammetry and involved three sections. The first section involved the investigation of the effect of additive concentration on polarisation as well as the investigation of additive molecular characteristics on polarisation. Furthermore, the results obtained were used to select the concentrations that were used for the rest of the work. Cyclic voltammetry experiments were conducted at 35 g/L copper at 40°C. The potentiostat was swept between 0.4 v vs Standard Hydrogen Electrode (SHE), and 0.07 v vs SHE, the scan rate was 5 mv/s and the electrolyte was stirred at 560 rpm using the rotating disk (cathode). The effects of additive concentrations of 1, 2, 10 and 20 mg/L on polarisation were investigated. For electrolytes at an additive concentration of 1 mg/L, polarisation was negligible. At 2 mg/L, polarisation increased with the decrease in molecular weight of the additive. However, at 10 and 20 mg/L, the inverse was reported. There was no significant difference between 10 and 20 mg/L, which prompted using 2 mg/L and 10 mg/L additive concentrations for further experiments. The second section involved the investigation of the effect of residence time on the polarisation behaviour of the additives as well as determining the additive dosage. At 2 mg/L, additive concentration polarisation decreased with time, and the additives were infective within 24 hours; however, at 10 mg/L, there was evidence of a degree of polarisation, prompting 10 mg/L as dosage for electrowinning experiments. The third section involved investigating the effects of copper at 35 g/L and 45 g/L and temperature at 40°C and 50°C. Copper concentration depolarised (increased) the copper reduction current density. However, introducing additives resulted in a less pronounced polarisation effect for 2 mg/L and 10 mg/L. Similar results were observed for the effect of temperature, where temperature depolarised the copper reduction process, however, the introduction of the additives resulted in a pronounced polarisation behaviour. The second phase involved bench electrowinning experiments with an electrolyte containing; 25 mg/L Cl- ,330 mg/L Mn2+, 2.0 g/ Fe3+, Co2+ 760 mg/L, H2SO4 170 g/L and 10 mg/L polyacrylamide. Effects of copper concentration (45-55 g/L) and temperature (40°C-50°C) were evaluated for current efficiency and specific energy consumption. Both factors positively affected efficiency and energy; this was evident by the increase in current efficiency and a decrease in specific energy consumption. Increasing temperature affected the molecular weight of the additives while increasing copper concentration affected the ionic charge of the additives. All the additives reduced the formation of nodulations. The last phase was stripping experiments which investigated the impact of the additives on phase disengagement time. were conducted at 25 mg/L Cl- , 330 mg/L Mn2+ , Fe3+ 2.0 g/L, Co2+ 760 mg/L, Cu2+ 40 g/L, 170 g/L H2SO4, and 10 mg/L PAM, the solutions were stirred at 700 rpm at A/0 ratio of 2.5. Phase disengagement time increased with the increase in additive concentration and molecular weight. The additive concentrations were varied from 2.5 mg/L to 10 mg/L. The results from this work can serve as a basis for polyacrylamide design for either direct electrowinning or the SX-EW integrated process. The molecular weight of the additives has a significant impact on the additives as well as their % ionic charge during electrowinning. It can be concluded that optimisation with respect to additive concentration is required for each operation to obtain an efficient process.en_ZA
dc.description.abstractAFRIKAANS OPSOMMING: Knoppiesvorming gedurende koperelektroherwinning bly ’n groot bedryfskommer omdat dit die energieverbruik van die bedryf verhoog en ook die kwaliteit van die koperplate verlaag. Afvlakmiddels word bygevoeg om knoppiesvorming te versag en die effektiwiteit van die proses te verbeter. Een van die opkomende moontlikhede is poliakrielamiedes. Navorsing het getoon dat poliakrielamiedes die potensiaal het om met die industrie se voorste bymiddels te kompeteer. Verder is dit ook gerapporteer dat molekulêre karakteristieke van poliakrielamiedes soos molekulêre gewig hul greinverfyningsdoeltreffendhede kan beïnvloed, i.e. vermindering van knoppiesvorming. Hierdie studie het die struktureel-verskillende poliakrielamiedbymiddels ondersoek in terme van hul viskositeit in die oplossing en hul persentasie ioniese lading. Hul karakteristieke is vergelyk in elektrochemiese metodes en toe in verband gebring met elektroherwinning. Verder, hierdie studie het ook die versoenbaarheid van die bymiddels met oplosmiddelekstraksie ondersoek, ’n bostroom proses van koperelektroherwinning. Hierdie studie is in drie fases gedeel. Die eerste fase was die fundamentele studie deur sikliese voltametrie te gebruik, en het drie afdelings ingesluit. Die eerste afdeling het die ondersoek van die effek van bymiddelkonsentrasie op polarisasie ingesluit, sowel as die ondersoek van bymiddel molekulêre karakteristieke op polarisasie. Verder, die resultate verkry is gebruik om die konsentrasies wat gebruik is vir die res van die werk, te selekteer. Sikliese voltametrie-eksperimente is uitgevoer by 35 g/L koper by 40°C. Die potentiostaat is gevee tussen 0.4 v vs. Standaard Waterstof Elektrode (SHE), en 0.07 v vs. SHE, die skandeerdertempo was 5 mv/s en die elektroliet is geroer by 560 rpm deur die draaiskyf (katode) te gebruik. Die effek van bymiddelkonsentrasies van 1, 2, 10 en 20 mg/L op polarisasie is ondersoek. Vir elektroliete by ’n bymiddelkonsentrasie van 1 mg/L, was polarisasie weglaatbaar. By 2 mg/L, het polarisasie verhoog met die afname in molekulêre gewig van die bymiddel. By 10 en 20 mg/L, is die inverse egter gerapporteer. Daar was geen beduidende verskil tussen 10 en 20 mg/L nie, wat aanleiding gegee het tot die gebruik van 2 mg/L en 10 mg/L bymiddelkonsentrasie vir verdere eksperimente. Die tweede afdeling het die ondersoek van die effek van verblyftyd op die polarisasiegedrag van die bymiddels ingesluit, sowel as die bepaling van die bymiddeldosering. By 2 mg/L het bymiddelkonsentrasiepolarisasie met tyd verminder, en die bymiddels was oneffektief binne 24 uur; by 10 mg/L was daar egter bewyse van ’n mate van polarisasie, wat aanleiding gegee het tot 10 mg/L as dosering vir elektroherwinningeksperimente. Die derde deel het die ondersoek van die effek van koper by 35 g/L en 45 g/L en temperatuur by 40 °C en 50 °C ingesluit. Koperkonsentrasie het die koperreduksiestroomdigtheid gedepolariseer (verhoog). Om bymiddels by te voeg het egter tot ’n minder duidelike effek vir 2 mg/L en 10 mg/L gelei. Soortgelyke resultate is waargeneem vir die effek van temperatuur, waar temperatuur die koperreduksieproses gedepolariseer het, maar die byvoeging van die bymiddels het egter tot ’n duidelike polarisasiegedrag gelei. Die tweede fase het banktoets-elektroherwinningeksperimente ingesluit met ’n elektroliet wat 25 mg/L CL- , 330 mg/L Mn2+ 2.0 g/L Fe3+, Co2+ 760 mg/L, H2SO4, 170 g/L en 10 mg/L poliakrielamiedes, bevat. Effek van koperkonsentrasie (45 – 55 g/L) en temperatuur (40 °C – 50 °C) is geëvalueer vir stroomdoeltreffendheid en spesifieke energieverbruik. Beide faktore het doeltreffendheid en energie positief beïnvloed; dit was duidelik met die verhoging in stroomdoeltreffendheid en ’n afname in spesifieke energieverbruik. Deur temperatuur te verhoog is die molekulêre gewig van die bymiddels geaffekteer terwyl koperkonsentrasie die ioniese lading van die bymiddels verhoog het. Al die bymiddels het die knoppiesvorming verminder. Die laaste fase was stropingseksperimente om die impak van bymiddels op fase-losmakingstyd te ondersoek. Eksperimente is uitgevoer by 25 mg/L Cl- , 330 mg/L Mn2+, 2.0 g/L Fe3+, Co2+ 760 mg/L+ . Cu2+ 40 g/L, H2SO4, 170 g/L en 10 mg/L poliakrielamiede die oplossings is geroer by 700 rpm by A/O verhouding van 2.5. Fase-losmakingstyd het gestyg met die verhoging van bymiddelkonsentrasie en molekulêre gewig. Die bymiddelkonsentrasies is gevarieer van 2.5 mg/L tot 10 mg/L. Die resultate van hierdie werk kan dien as ’n basis vir poliakrielamiedontwerp vir óf direkte elektroherwinning óf die SX-EW geïntegreerde proses. Die molekulêre gewig van die bymiddels het ’n beduidende impak op die bymiddels sowel as hul persentasie ioniese lading gedurende elektroherwinning. Die slotsom is dat optimering met betrekking tot bymiddelkonsentrasie vereis word vir elke bedryf om ’n doeltreffende proses te verkry.af_ZA
dc.description.versionMastersen_ZA
dc.format.extentxv, 115 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/127367en_ZA
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshPolyacrylamideen_ZA
dc.subject.lcshMolecular weightsen_ZA
dc.subject.lcshCopper--Electrometallurgyen_ZA
dc.titleInvestigation of characteristics of polyacrylamide-based additives for copper electrowinningen_ZA
dc.typeThesisen_ZA
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