With current energy demands globally and locally, nuclear energy remains one of the top competitors for cleaner and sustainable energy. The nuclear industry requires more inherent safety and proliferation resistance in reactor design. Thorium has therefore been identified as a possible fuel for future nuclear reactors that can comply with these requirements. However current extraction techniques are expensive, time consuming and generate large quantities of hazardous waste. A possible alternative to conventional solvent extraction of thorium is SFE (Supercritical Fluid Extraction). A monazite sample from the Steenkampskraal mine was investigated using SEM (Scanning Electron Microscope) analysis methods to determine the distribution of thorium in the grains that could potentially complicate the effectiveness of the SFE extraction method if zoning is present. The results show a homogeneous distribution with no discernable zonation in the grains. The concentration of Th, Ce and Nd was determined by quantitative MPA (Micro Probe Analysis). The results obtained from the MPA point analysis on several grains show average Th, Ce and Nd concentrations of 6.5 wt. %, 24.1 wt. % and 9.7 wt. % respectively. The extraction of Th+4 from a filter paper was conducted to verify the extraction procedure and extractability of transition elements employing SFE. The extraction was conducted using supercritical CO2 and methanol as co-solvent with TBP (Tributyl Phosphate) and HFA (Hexafluoroacetylacetone) added in situ as chelates. ICP-MS results for the Th+4 extraction procedure showed extraction efficiency of 53 % compared to 83 % in literature (Kumar et al. 2009). This marked difference in extraction efficiency is attributed to ineffective trapping methods employed and lack of prior maintenance and support on the extraction apparatus. Subsequently all further extracted samples of Th from monazite were tested using XRF analysis methods. Due to the lack of prior maintenance on the extraction apparatus several technical breakdowns were encountered and addressed from a mechanical engineering standpoint. The operational effectiveness of the modified apparatus was verified through the extraction of marula seed oil and compared with another supercritical fluid (SF) extractor to show 50 % extraction efficiency in each case. A review of the literature indicated that the crystal chemical requirements for substitution of trivalent (Ce+3) for tetravalent (Th+4) may be fulfilled during SFE processes. Experimental substitution extractions were conducted by addition of different chelates and were conducted by subjecting the monazite samples to 20 MPa pressure for 180 min static flow and 10 min continuous flow extraction times with a CO2 flow rate of 2 mL/min with 10 % co-solvent flow rate. The results of the two sets of substitution extractions namely α and β show no clear indication of Th extraction. The maximum theoretical efficiency obtainable under current extraction equipment limitations was calculated as 12%. The XRF analysis error margin was given by the analytical laboratory as 10 %. The literature has shown the substitution of trivalent cations for tetravalent cations in the monazite structure to be a valid reaction mechanism. The experimental results showed little or no success in extracting thorium from monazite. In order to prove the practical feasibility of thorium extraction several changes to the experimental operating conditions is required. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

Chalcopyrite ore forms the significant fraction of copper deposits in the earth crust. However, it is also the most difficult to treat using conventional ferric leaching methods. Smelting and electro-refining are currently the methods used in treating chalcopyrite concentrate obtained from froth flotation. Due to the ever increasing environmental requirements on smelters by the Environmental Protection Agency, new smelters are scarce in the United States. The scarcity of smelters has led to the urgent need to find a novel leaching method for the abundant chalcopyrite deposits in the USA and the rest of the world. This chapter(one) of the dissertation, therefore, investigated the leaching of chalcopyrite ore at pH 2 using a newly discovered oxidant (peroxodisulfate). Our results show that chalcopyrite leaching using peroxodisulfate follows a surface reaction shrinking core model. The activation energy of chalcopyrite leaching using peroxodisulfate ion was calculated as 41.1 kJ mol⁻¹. We also report that the leaching of chalcopyrite ore is affected by particle size and that stirring hurts leaching of chalcopyrite. Additionally, we found that peroxodisulfate can produce from sulfuric ions electrochemically. Hydrogen peroxide, permanganate, peroxodisulfate and ferric ions are all strong oxidants that have been researched in production pregnant leach solution (PLS) from chalcopyrite ore leaching. Because, solvent extraction is the next step in the recovery of copper from pregnant leach solutions (PLS). The questions, therefore, arises as to the fate of the organic extractant used in solvent extraction coming in contact with strong oxidant residual in the PLS. In chapter two of the dissertation, we studied the effect of strong oxidant residual in PLS on the degradation of organic extractants during solvent extraction of copper. Exposed organic extractants were analyzed using interfacial tension(IFT), Fourier Transform Infrared (FTIR) spectroscopy and CG LS. The results obtained from IFT and FTIR analysis, show no effect on the organic extractants exposed to sunlight and PLS containing the residual strong oxidant. Finally in chapter 3, the dissertation exams alternative water source for the flotation of chalcopyrite. Mineral flotation is a water-intensive process in mining. In order to sustain mining operations such flotation, which rely heavily on water, chapter 3 of the dissertation looks at using alternative water sources (in this case reclaimed wastewater) in the flotation of chalcopyrite ores; this effort is to limit the mining industries dependence on fresh ground water particularly in the Southwest of United States where water is a scarce commodity. The research studied the effect of reclaimed waste water on chalcopyrite flotation via contact angle and surface energy measurements. Furthermore, atomic force microscopy (AFM) and flotation tests were used to supplement the findings from contact angle and surface studies. We conclude here that the contact angle of a pure chalcopyrite surface was determined to be 75.6 degrees. We also found that pure chalcopyrite mineral surface is slightly polar with surface energies γCuFeS2^(LW) = 41.4 mJ/m² (apolar), γCuFeS2^(AB) = 2.9 mJ/m² (polar). The high value of the surface energy indicates pure chalcopyrite surface is slightly hydrophobic.

Dissertation (PhD(Eng))--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Coal pyrolysis liquors are a major source of phenolic compounds. The separation of the phenolic compounds from the neutral oils and nitrogen bases also present in the pyrolysis liquors is difficult due to low relative volatilities and the formation of azeotropes. The desired phenolic recovery and phenolic product purity of 99.5 % can therefore not be achieved by means of conventional separation processes. Alternative processes such as liquid-liquid extraction with various low-boiling solvents, mixtures of high-boiling solvents and extractive distillation have been investigated. Disadvantages of these processes include the high solvent ratios required, low recovery of the higher substituted phenolic compounds, inability to treat a wide-boiling feedstock in one process step and complex post-purification of the phenolic product. A solvent system consisting of a selective solvent, water as a co-solvent, and hexane as a countersolvent, is proposed. An industrial heavy naphtha stream was analysed and the most prevalent phenolic compounds, neutral oils and nitrogen bases identified. Three synthetic feed streams were compiled to represent the industrial stream, namely: 1. phenol + benzonitrile + aniline + mesitylene + 5-et-2-me-pyridine 2. m-cresol + o-tolunitrile + o-toluidine + pseudocumene + undecane + indene 3. 2,4-xylenol + 3,5-xylenol + 3,4-xylenol + indane + dodecane + naphthalene The stream containing phenol was used as a basis for solvent selection, with emphasis on the separation of phenol from benzonitrile. A variety of molecules containing hydroxyl and ether functional groups were identified as potential solvents by means of computer-aided molecular design using a genetic algorithm. Of the commercially available solvents tested on batch extraction scale, triethylene glycol achieved the highest phenol-benzonitrile, phenol-aniline and phenol-5-et-2-me-pyridine separation factors as well as the highest phenol recovery. It was concluded from the solvent selection process that effective solvents for the problem under investigation were those containing hydroxyl groups positioned on the molecule backbone in such a way as to facilitate hydrogen bonding with more than one phenolic molecule at a time. Two commercially unavailable solvents, 1,3-(ethoxy-2- hydroxy)-propane-2-01 and 1,3-(diethoxy-4-hydroxy)-propane-2-01 were therefore synthesised from ethylene glycol and diethylene glycol respectively. The molecular structures of these two solvents are analogous to that of triethylene glycol, and contain an additional hydroxyl group. The performance of the synthesised solvents was evaluated and compared to that of triethylene glycol on the basis of m-cresol-otolunitrile, 2,4-xylenol - o-tolunitrile, and 2,4-xylenol - o-toluidine separation factors and phenolic recoveries achieved by means of batch extraction tests. 1,3-(Diethoxy-4- hydroxy)-propane-2-01 yielded higher phenolic recoveries, but lower separation factors than did triethylene glycol. Triethylene glycol was therefore selected for further process development as it is commercially available. A series of batch extractions were carried out on each of the synthetic feed streams using the proposed solvent system. For phenol and m-cresol, recoveries in excess of 99% were obtained in a single stage. Recoveries in excess of 98% were obtained for the xylenol isomers. It was found that the recoveries of the xylenol isomers were more sensitive to changes in the solvent ratios. The separation of phenolic compounds from paraffins, naphthalene, indene, indane and the alkyl-substituted benzenes was trivial using the proposed solvent system. Highly satisfactory separation of the phenolic compounds from pyridines and aromatic nitriles was achieved. The separation of phenol from aniline, although satisfactory, was not as good. The optimum solvent to feed, water to solvent and hexane to feed ratios were identified as being 3.0, 5.0 and 0.25 respectively. Binary interaction parameters for the NRTL equation were obtained by regression of the equilibrium data from the batch extraction tests. The NRTL model fitted the equilibrium data satisfactorily. The proposed solvent system was tested on pilot plant scale. The performance of the extraction column was optimised using a synthetic feed stream consisting of m-cresol, p-cresol, aniline and o-tolunitrile. The optimum solvent ratios and operating parameters were then implemented in further tests on an industrial heavy naphtha stream. A phenolic product purity of 99.75% was achieved for this stream. The corresponding phenolic recovery was in excess of 91 %. The proposed separation process, including solvent recovery was simulated using the NRTL model with the experimentally determined interaction parameters. A single stream consisting of all the components used in the batch extraction tests was specified as the feed stream to the simulated process. A final simulated phenolic product purity of 99.5% and recovery in excess of 94% was obtained after solvent recovery. The optimum solvent to feed, hexane to feed and water to solvent ratios were determined as being 3.0, 5.0 and 0.25 in both the pilot plant tests and the simulated extraction process. It can be concluded that the proposed separation process is successful in recovering high purity phenolic compounds from tar liquors. Further development of the process has commenced in industry. / AFRIKAANSE OPSOMMING: Die pirolise van steenkool is 'n belangrike bron van fenoliese verbindings. Die skeiding van die fenoliese komponente vanuit die neutrale olies ook teenwoordig in die pirolise mengsel word bemoeilik deur lae relatiewe vlugtighede en die vorming van aseotrope. Dit is dus nie moontlik om die gewenste hoë fenoliese herwinning en fenoliese produk suiwerheid van 99.5% d.m.v. konvensionele distilleerprosesse te behaal nie. Alternatiewe prosesse soos ekstraktiewe distillasie en vloeistof-vloeistof ekstraksie met verskeie laagkokende oplosmiddels en mengsels van hoogkokende oplosmiddels is al ondersoek. Die hoë oplosmiddel verhoudings wat benodig word, lae herwinning van die hoërgesubstitueerde fenoliese verbindings, onvermoë om in een prosesstap 'n prosesstroom met In wye kookgebied te behandel en die ingewikkelde suiwering van die fenoliese produk tel onder die nadele van hierdie prosesse. 'n Oplosmiddelsisteem wat In selektiewe oplosmiddel, water as polêre oplosmiddel en heksaan as teenoplosmiddel bevat is as 'n alternatiewe proses voorgestel. 'n Industriële swaar nafta prosesstroom is ge-analiseer en die fenoliese verbindings, neutrale olies en stikstofbasisse met die hoogste konsentrasies daarin geïdentifiseer. Drie sintetiese strome is op grond van hierdie analise saamgestelom die industriële stroom te verteenwoordig: 1. fenol + benzonitriel + anilien + mesitileen + 5-et-2-me-piridien 2. m-kresol + o-tolunitriel +o-toluïdien + pseudokumeen + undekaan + indeen 3. 2,4-xilenol + 3,5-xilenol + 3,4-xilenol + indaan + dodekaan + naftaleen Die fenolbevattende stroom is as basis vir oplosmiddelkeuring gebruik, met die klem op die skeiding van fenol vanuit benzonitriel. Verskeie molekules wat hidroksie- en eter funksionele groepe bevat is as potensiële oplosmiddels uitgeken d.m.v. rekenaargesteunde molekulêre ontwerp met In genetiese algoritme. Hierdie oplosmiddels is d.m.v. enkellading ekstraksie toetse geëvalueer. Die kommersieel beskikbare oplosmiddel wat die hoogste fenol-benzonitriel, fenol-anilien en fenol-5-et-2-me-piridien skeidingsfaktore, sowel as die hoogste fenol herwinning op enkellading ekstraksie toetsvlak gelewer het, was triëtileenglikol. Vanuit die proses vir die keuse van 'n oplosmiddel was dit duidelik dat, vir hierdie skeidingsprobleem, die mees effektiewe oplosmiddels dié is met hidroksiel groepe wat so geposisioneer is in die oplosmiddel molekuul dat dit waterstofbindings kan vorm met meer as een fenoliese molekuul. Twee oplosmiddels wat nie kommersiëel beskikbaar is nie, 1,3-(etoksie-2-hidroksie)-propaan-2-01 en 1,3-(diëtoksie-4-hidroksie)-propaan-2- ol, is gesintetiseer vanuit etileenglikol en diëtileenglikol onderskeidelik. Die molekulêre strukture van hierdie twee oplosmiddels is analoog aan dié van triëtileenglikol en bevat 'n addisionele hidroksielgroep. Die effektiwiteit van die gesintetiseerde oplosmiddels is geëvalueer en met dié van triëtileenglikol vergelyk op grond van rn-kresol-o-tolunltriel, 2,4-xilenol - o-tolunitriel en 2,4-xilenol - o-toluïdien skeidingsfaktore en fenoliese herwinning behaal d.m.v. enkellading ekstraksie toetse. Hoër fenoliese herwinning en laer skeidingsfaktore is behaal met 1,3-(diëtoksie-4-hidroksie)-propaan-2-01as met triëtileenglikol. Triëtileenglikol is dus gekies vir verdere prosesontwikkeling aangesien dit kommersiëel beskikbaar is. Enkellading ekstraksie toetse is op elk van die sintetiese voerstrome uitgevoer met die voorgestelde oplosmiddelsisteem. Fenol- en m-kresol herwinning van meer as 99% en xilenol herwinning van meer as 98% is behaal. Die skeiding van fenoliese verbindings vanuit paraffiene, naftaleen, indeen, indaan en die alkielgesubstitueerde benseenverbindings is triviaal met die voorgestelde oplosmiddelsisteem. Hoogs aanvaarbare skeiding van fenoliese verbindings van die piridiene en aromatiese nitriele is vermag. Die skeiding van fenol en anilien is nie so goed nie, maar is nog steeds aanvaarbaar. Die optimum oplosmiddel tot voer, water tot oplosmiddel en heksaan tot voer is as 3.0, 5.0 en 0.25 vasgestel. Binêre interaksie parameters vir die NRTL vergelyking is verkry d.m.v. regressie van die ewewigsdata wat deur die enkelladingstoetse gegenereer is. Die NRTL model het die ewewigsdata goed gepas. Die voorgestelde oplosmiddelsisteem is op loodsaanlegvlak getoets. Die werking van die ekstraksie kolom is ge-optimeer met In sintetiese voerstroom wat uit m-kresol, pkresol, anilien en o-tolunitriel bestaan. Die optimum oplosmiddel verhoudings en bedryfstoestande is verder toegepas op 'n industriële swaar naftastroom. 'n Fenoliese suiwerheid van 99.75% is behaal met hierdie stroom. Die ooreenkomstige fenoliese herwinning was groter as 91%. Die voorgestelde skeidingsproses, insluitende oplosmiddelherwinning is gesimuleer met die NRTL model wat op die eksperimentele data gepas is. 'n Enkele stroom wat bestaan het uit al die komponente wat in die enkelladingstoetse gebruik is, is as die voerstroom tot die gesimuleerde proses gespesifiseer. 'n Finale gesimuleerde fenoliese produksuiwerheid van 99.5% en herwinning groter as 94% is na oplosmiddelherwinning behaal. Die optimum oplosmiddel tot voer, heksaan tot voer en water tot oplosmiddel verhoudings is vasgestel as 3.0, 5.0 en 0.25 onderskeidelik vir beide die gesimuleerde proses en die loodsaanleg toetse. Die voorgestelde skeidingsproses kan dus 'n hoogs suiwer fenoliese produk uit pirolisestrome herwin. Verdere ontwikkeling van die proses is in die industrie begin.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Crude NiSO4 solutions are often produced as a product of Sherrit based matte leach processes leading to iron and cobalt contaminated solutions of NiSO4. To upgrade the quality of these solutions for either, the production of NiSO4 crystals or cathode/precipitated nickel, the iron and cobalt must be removed. Conventional processes use either pure or saponified Cyanex 272 in solvent extraction to extract iron and cobalt from pregnant nickel leach solutions. These processes require the addition of an alkali like NaOH to neutralise the protons being exchanged for the different metal species since extraction is a strong function of pH. Hence, while removing iron and cobalt from the solution, sodium is added instead. This limitation can be dealt with by pre-loading of Cyanex 272 with a portion of the purified nickel product prior to impurity extraction. During the extraction stage nickel is then exchanged for the impurities instead of hydrogen and no NaOH addition is necessary, resulting in a pure nickel product. The extracted metals are recovered from the organic phase by stripping it with H2SO4 and the organic phase is recycled. A solvent extraction process that purifies an 80 g/l nickel sulfate solution from 1 g/l cobalt and 3 g/l iron was developed. The key variables include pH, organic/aqueous (O/A) mixing ratio, nickel loading, H2SO4 concentration, Cyanex 272 concentration, various organic diluents and temperature. These variables were investigated via preliminary and three 24 factorial design batch experiments which reduced the variables to pH/NaOH addition and O/A ratio for the pre-loading section, nickel loading and O/A ratio for the extraction section and H2SO4 concentration and A/O ratio for the stripping section. The reduced variables were considered in further batch experiments from which the data was used to develop models and design a simulation sheet in Microsoft Excel of the extraction circuit. These final batch tests revealed the conditions that resulted in the purest aqueous nickel product after extraction, where nickel and cobalt can selectively be stripped from iron and what H2SO4 concentration and A/O ratio is necessary to finally strip iron and regenerate the organic phase. Ultimately four tests were conducted on a mixer-settler setup to test the validity of the simulation sheet. The proposed process conditions for the solvent extraction circuit are to use a 20V% Cyanex 272 solution in Shellsol D70 as diluent that are pre-loaded with an 80 g/l purified nickel product solution at an O/A ratio of 25 and a pH of 7 generating a nickel loading of 3.2 g/l for the extraction section. This loading at an O/A ratio of 1.5 produces a high pure nickel aqueous product (0.05 g/l Co, 0.01 g/l Fe). From the generated organic phase co-extracted nickel and cobalt can selectively be stripped with 0.1 M H2SO4 at an A/O ratio of 2.25 followed by an 1 M H2SO4 solution at an A/O ratio of 0.75 to strip the remaining iron. The temperature at all the stages should be controlled between 40-50°C to ensure phase separation. / AFRIKAANSE OPSOMMING: Ongesuiwerde NiSO4 oplossings word gedurig vervaardig as ʼn produk van die Sherrit gebaseerde mat logingsproses wat lei tot yster en kobalt gekontamineerder oplossings van NiSO4. Om die graad van hierdie oplossings op te gradeer vir die produksie van of NiSO4 kristalle of katode/gepresipiteerde nikkel, moet die yster en kobalt eers verwyder word. Meeste prosesse gebruik of suiwer Cyanex 272 of die natrium sout van Cyanex 272 in ʼn vloeistof-vloeistof ekstraksie siklus om yster en kobalt vanuit versadigde nikkel oplossing te ekstraheer. Hierdie prosesse verg die gebruik van ʼn alkali soos NaOH om die protone te neutraliseer wat geruil word vir die verskillende metaal spesies, aangesien ekstraksie ʼn baie sterk funksie van pH is. Dit het tot gevolg dat natrium tot die oplossing bygevoeg word soos wat yster en kobalt verwyder word. Hierdie tekortkoming kan oorkom word deur Cyanex 272 eers te laai met nikkel deur ʼn porsie van die gesuiwerde nikkel produk te gebruik voor die onsuiwerhede geëkstraheer word. Gedurende die ekstraksie stadium word nikkel dan geruil vir die onsuiwerhede, in plaas van waterstof, en geen NaOH toevoeging is nodig nie. Die gevolg is ʼn suiwer nikkel oplossing. Die geëkstraheerde metaal word herwin vanaf die organies fase deur dit te stroop met ʼn H2SO4 oplossing en die organiese fase kan weer gehersirkuleer word. ʼn Vloeistof-vloeistof ekstraksie proses wat ʼn 80 g/l nikkelsulfaat oplossing van 1 g/l kobalt en 3 g/l yster suiwer, is ontwikkel. Die belangrikste veranderlikes sluit in pH, organies/waterige (O/A) mengingsverhouding, nikkel lading, H2SO4 konsentrasie, Cyanex 272 konsentrasie, verskillende organiese oplosmiddels en temperatuur. Hierdie veranderlikes was ondersoek deur verskeie voorlopige en drie 24 faktoriaal ontwerp enkel-lading eksperimente wat gevolglik die veranderlikes verminder het na pH/NaOH toevoeging en O/A verhouding vir die voorbelading seksie, nikkel lading en O/A verhouding vir die ekstraksie seksie en H2SO4 konsentrasie en A/O verhouding vir die stroping seksie. Die verminderde veranderlikes was verder ondersoek in nog enkel-lading eksperimente, waarvan die data gebruik was om modelle op te stel en ʼn simulasie sigblad in Microsoft Excel te ontwerp van die ekstraksie siklus. Die finale enkel-lading toetse het die kondisies weergegee wat die mees suiwer waterige nikkel produk sal oplewer na ekstraksie, waar kobalt en nikkel selektief van yster gestroop kan word en watter H2SO4 konsentrasie en A/O verhouding nodig is om yster finaal te stroop en die organiese fase te regenereer. Laastens is vier toetse gedoen op ʼn menger-afskeidingstenk opstelling om die betroubaarheid van die simulasie sigblad te toets. Die bedryfstoestande wat voorgestel word vir die vloeistof-vloeistof ekstraksie siklus is om ʼn 20V% Cyanex 272 oplossing in Shellsol D70 as oplosmiddel vooraf te laai met ʼn 80 g/l gesuiwerde nikkel produk oplossing by ʼn O/A verhouding van 25 en ʼn pH van 7 om ʼn nikkel lading van 3.2 g/l vir die ekstraksie seksie te genereer. Hierdie lading by ʼn O/A verhouding van 1.5 produseer ʼn suiwer nikkel waterige oplossing produk (0.05 g/l Co, 0.01 g/l Fe). Vanaf die gegenereerde organiese fase kan die geëkstraheerde nikkel en kobalt selektief gestroop word met 0.1 M H2SO4 by ʼn A/O verhouding van 2.25 gevolg deur ʼn 1 M H2SO4 oplossing by `n A/O verhouding van 0.75 om die oorblywende yster te stroop. Die temperatuur waarby al die stadiums beheer moet word is tussen 40-50°C om fase skeiding te verseker.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: At Skorpion Zinc mine, in south-west Namibia, zinc oxide ore is refined through sulphuric acid leaching, solvent extraction, electrowinning and casting of the final 99.995 % Zn metal. Over the last four years, the rare earth element concentrations, with particular reference to Y, Yb, Er and Sc, have significantly increased in the circulating electrolyte and the zinc-stripped organic phase streams in the electrowinning and solvent extraction processes. This project had two main objectives: firstly, the effect(s) of rare earths on the zinc solvent extraction and electrowinning processes were to be determined; based on these results, the second objective was to find a suitable method for removing rare earth elements from the organic phase during zinc solvent extraction. The investigation into the effect of the rare earths on zinc electrowinning showed that an increase of 100 mg/l in the electrolyte Y concentration caused a decrease of 6 % in current efficiency. The elemental order of decreasing current efficiency was found to be: Y > Yb > Er > Sc. In the zinc solvent extraction process, it was found that an increase in the total organic rare earth elements and iron concentration from 3100 to 6250 mg/l resulted in doubled viscosity and an increase in phase disengagement time from 100 to 700 seconds. The organic zinc loading capacity after two extraction stages was reduced by 1 – 3 g/l depending on the pregnant leach solution used. The detrimental effect of rare earth elements on solvent extraction and electroplating of zinc therefore justified the development of a rare earth element removal process. Stripping of low concentrations of rare earth elements from 40% D2EHPA diluted in kerosene to produce a clean organic for zinc extraction was investigated using bench-scale experiments in a glass jacketed mixing cylinder. For the rare earths, the best stripping agent was found to be H2SO4, followed by HCl and then HNO3. Hydrochloric acid achieved better Fe stripping than sulphuric acid. Acid concentration was tested in the range of 1 to 7 M, organic-to-aqueous ratio for the range of 0.25 to 6.0 and temperatures between 30 and 55 °C. More than 80% stripping of yttrium and erbium could be achieved at an optimum hydrochloric acid concentration of 5 M and more than 90% rare earth element (specifically Y, Er, Yb) stripping from the organic phase could be achieved with 5 M sulphuric acid. Stripping was improved by reducing the organic-to-aqueous ratio to as low as 0.5 and increasing the temperature. Stripping increased with increasing temperature in an S-shaped curve, flattening off at 50°C. The effect of O:A ratio was more significant than the effect of temperature on rare earth stripping. The results showed good repeatability, and were not limited by the rare earth concentration, agitation rate or equilibrium time in the range of set points used in the experiments. Statistical models were compiled to fit the experimental data obtained for Y, Yb, Er and Fe when stripped with sulphuric and hydrochloric acid respectively. All models showed dependence on the acid concentration and squared-concentration and interaction effects between the O:A ratio and temperature and stripping agent concentration were significant. The models were compiled for the experimental data obtained from stripping synthetically prepared organic and then tested on results obtained when stripping the plant organic phase. The following three process solutions were discussed for implementation on a plant scale for the removal of rare earths from the organic phase during zinc solvent extraction: Sulphuric acid stripping mixer settler or stripping column, improvement of available HCl stripping section and replacement of the organic inventory. The possibility of an oxalic acid precipitation process to obtain value from the rare earths as by-product was also discussed. It was concluded that the current process that uses HCl to strip off iron and rare earths would be the best practically and financially feasible process. Value can be gained from the rare earths if a rare earth element - oxalic acid precipitation section that is financially feasible can be established. / AFRIKAANSE OPSOMMING: By Skorpion Zinc myn, in suidwes Namibië, word sinkoksied erts gesuiwer deur middel van swaelsuur-loging, oplosmiddel ekstraksie, elektroplatering en gieting van die finale 99.995 % Zn metaal. Oor die afgelope vier jaar het die seldsame aardmetale konsentrasie, spesifiek Y, Yb, Er en Sc, noemenswaardig in die sirkulerende elektroliet en sink-gestroopte organiese fase toegeneem. Hierdie projek het twee hoofdoelstellings gehad: eerstens moes die effek van seldsame aardmetale op die sink oplosmiddel ekstraksie en elektroplatering prosesse bepaal word; gebaseer op hierdie resultate, was die tweede doelstelling om ‘n geskikte metode vir die verwydering van seldsame aardmetale vanaf die organiese fase gedurende sink oplosmiddel ekstraksie te vind. Die ondersoek na die effek van seldsame aardmetale op sink elektroplatering het gewys dat ‘n verhoging van 100 mg/l in die elektroliet Y konsentrasie ‘n verlaging van 6 % in kragdoeltreffendheid veroorsaak het. Die element-orde van verminderende kragdoeltreffendheid was Y > Yb > Er > Sc. Vir die sink oplosmiddel ekstraksie proses, is gevind dat ‘n verhoging in die totale organiese seldsame aardmetaal- en yster konsentrasie van 3100 tot 6250 mg/l ‘n verdubbelde viskositeit en ‘n verlenging in faseskeidingstyd van 100 tot 700 sekondes tot gevolg gehad het. Die organiese sink ladingskapasiteit na twee ekstraksie stappe is met 1 – 3 g/l verminder afhangende van die logings oplossing wat gebruik is. Die nadelige effek van seldsame aardmetale op oplosmiddel ekstraksie en sink elektroplatering het die ontwikkeling van ‘n seldsame aardmetale verwyderingsproses regverdig. Die verwydering van lae konsentrasies seldsame aardmetale vanaf die D2EHPA-keroseen organiese fase om ‘n skoon organiese fase vir sink-ekstraksie te verkry is ondersoek deur banktoetsskaal eksperimente. Vir die seldsame aardmetale is bevind dat H2SO4 die beste stropingsagent is, gevolg deur HCl en dan HNO3. Soutsuur het beter yster verwydering as swaelsuur bewerkstellig. Suurkonsentrasies van 1 tot 7 M, O:A verhoudings van 0.25 tot 6 en temperature tussen 30 en 55°C is getoets. Meer as 80% verwydering van yttrium en erbium kon bereik word met ‘n optimum HCl konsentrasie van 5 M en meer as 90% seldsame aardmetale (spesifiek Y, Er en Yb) verwydering vanaf die organiese fase met 5 M swaelsuur. Seldsame aardmetale en yster verwydering kon verbeter word deur die organies-tot-waterfase (O:A) verhouding te verminder tot so laag as 0.5 en deur die temperatuur te verhoog. Stroping het in ‘n S-kurwe verhoog soos die temperatuur verhoog het, en het afgeplat teen 50°C. Die effek van die O:A verhouding was belangriker as die effek van temperatuur op stroping. Die resultate het goeie herhaalbaarheid gewys, en is nie deur massaoordrag beperk nie. Statistiese modelle is saamgestel om die eksperimentele data wat vir Y, Yb, Er en Fe verkry is vir stroping met swaelsuur en soutsuur te pas. Al die modelle het afhanklikheid van die suurkonsentrasie en kwadratiese suurkonsentrasie gewys en interaksie effekte tussen die O:A verhouding, temperatuur en suurkonsentrasie was belangrik. Die modelle is saamgestel vir die eksperimentele data wat verkry is vanaf stroping van ‘n sintetiese organiese fase en is toe getoets op resultate wat verkry is vanaf stroping van die aanleg se organiese fase. Die volgende drie proses-oplossings is oorweeg vir implementering op ‘n aanlegskaal vir die verwydering van seldsame aardmetale vanaf die organiese fase gedurende sink oplosmiddel ekstraksie: Swaelsuur stroping menger-afskeidingstenk of stropingskolom, verbetering van die bestaande HCl aanleg en vervanging van die organiese inventaris. ‘n Moontlike oksaalsuur presipitasie proses om waarde vanaf die seldsame aardmetale as by-produk te verkry is ook bespreek. Daar is tot die gevolgtrekking gekom dat die huidige proses wat HCl gebruik om yster en seldsame aardmetale van die organiese fase af te stroop, die beste praktiese en finansieel vatbare proses huidiglik is. Waarde kan vanaf die seldsame aardmetale verkry word as ‘n seldsame aardmetale – oksaalsuur presipitasie afdeling wat finansieel haalbaar is daargestel kan word.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this study an economical, environmentally friendly, selective and efficient process for the extraction and recovery of [AuCl4]- from aqueous acidic chloride-rich solutions, particularly those aqueous solutions having low concentrations of the precious metal complexes has been investigated. Functionalized poly(styrene-co-maleimide) (PSMI) nanoparticles were synthesized by thermal imidization of the poly(styrene-co-maleic anhydride) (PSMA) copolymer with 3-N,N-dimethylaminopropylamine. Stable water-based dispersions were obtained containing spherical, monodisperse PSMI nanoparticles with a narrow size-distribution and average diameters of 50 ± 5 nm. The specific surface area of the bulk PSMI nanoparticles is 88.1 ± 2.2 m2/g with an average pore diameter of 82.3 Å. 13C NMR, FTIR and elemental analyses confirmed the successful and complete conversion of PSMA into the PSMI derivative. The functionalized PSMI nanoparticles synthesized were investigated as a novel anion-exchange material for the extraction of [AuCl4]- ions from aqueous acidic solutions. Batch sorption studies were carried out as a function of various parameters, such as initial gold concentration, PSMI mass, contact time and agitation rate. The [AuCl4]- extraction occurred with extremely fast sorption kinetics and is dependent on the rate of agitation during the batch sorption process. The functionalized PSMI nanoparticles show a maximum gold loading capacity of 1.76 mmol/g (347.7 mg/g). Langmuir and Freundlich isotherm models were applied to analyze the experimental sorption data. The best model describing the sorption process is given by the Langmuir model. Desorption efficiencies of about 80 % and 93 % were obtained using acidified thiourea (0.25 M thiourea/2 M HCl) and a mixture of 10 M HNO3/0.5 HCl as elutant solutions, respectively. X-ray photoelectron spectroscopy (XPS) analysis unambiguously confirms that the immobilized gold species exists in several oxidation states of 0, +I and +III on the PSMI nanoparticles. This proves that the [AuCl4]- ions initially present in the gold feed solutions unfortunately are subject to a reduction phenomenon on the surface of the functionalized PSMI nanoparticles. The existence of the various gold species contributed significantly to poor desorption efficiencies. In addition to PSMI nanoparticles, micro- to millimeter size PSMI resin beads was prepared by an electrospray methodology. This allows for a wide range of PSMI spherical and quasi-spherical bead diameters of shape to be prepared by manipulation of the experimental conditions employed during the electrospray process, such as the concentration of the PSMI in solution, the capillary tip-to-collector distance, flow rate and the applied voltage. 13C NMR and FTIR spectroscopy analyses show that the electrospray methodology allows PSMI resin beads preparation without any change in chemical composition of the PSMI material. Surface area and porosity analysis shows that 450 μm and 1620 μm PSMI beads selected for use in the gold extraction experiments are microporous and have BET specific surface areas of 2.8 ± 0.4 m2/g and 2.0 ± 0.1 m2/g, respectively. Micro- to millimeter size PSMI resin beads of 450 μm and 1620 μm diameter were tested as potential anion-exchange resins for the extraction of [AuCl4]- from aqueous acidic solutions. The time-dependent studies reveal that the extent of gold uptake increases with an increase in contact time and is dependent on the gold concentration in the [AuCl4]- feed solutions. A maximum loading capacity of 120.7 mg/g and 98.16 mg/g was attained for the 450 μm and 1620 μm resin beads, respectively. The experimental sorption data followed a linear trend consistent with a Freundlich sorption model. This sorption trend for [AuCl4]- suggests that a multi-layer sorption process predominates. Desorption of immobilized gold species from the loaded PSMI resin beads was investigated using various elutants such as HCl, HNO3, thiourea, NaCN and NaOH solutions. The best results were obtained using a mixture of 10 M HNO3/0.5 M HCl as elutant with a desorption efficiency of about 97%. Finally, superparamagnetic magnetite (Fe3O4) nanoparticles with a high degree of crystallinity and phase purity were synthesized by a chemical co-precipitation of Fe2+ and Fe3+ salts. The average diameters of the obtained Fe3O4 nanoparticles were about 7 – 8 nm. The Fe3O4 nanoparticles were coated with oleic acid surfactant molecules and used as seed particles for the preparation of 50 nm diameter magnetic PSMI nanoparticles via an in situ imidization reaction. TEM analysis confirmed that the magnetically responsive PSMI nanoparticles consist of magnetite core-polymer shell structure, although more work is required to perfect such materials. / AFRIKAANSE OPSOMMING: In hierdie studie is ‘n ekonomiese, omgewings vriendelike, seleketiewe en effektiewe proses vir die ekstraksie en herwinning van [AuCl4]- uit suur chloried-ryke oplossings, spesifiek oplossings van lae konsentrasies van edel metal komplekse was bestudeer. Gefunksionaliseerde poli(stireen-ko-maleïmied) (PSMI) nanopartikels was gesintetiseer deur middel van termiese imidisasie van die poli(stireen-ko-maleïk anhidried) kopolimeer met 3-N,N-dimetielaminopropielamien. Stabiele dispersies in water was gevind wat soos sweriese mono-disperse PSMI nanopartikels met ‘n noue partikel-grootte verspreiding met ‘n gemiddelde deursnee van 50 ± 5 nm. Die spesifieke oppervlak area van die massa PSMI nanopartikels is 88.1 ± 2.2 m2/g met ‘n gemiddelde porie-grootte van 82.3 Å. 13C NMR, FTIR en elementêre analiese bevestig die suksesvolle en volledige omskakeling van PSMA na PSMI. Die gefunksionaliseerde PSMI nanopartikels was bestudeer as ‘n nuwe anion-uitruil material vir die ekstraksie van [AuCl4]- ione uit suur oplossings. Stel sorpsie studies was uitgevoer as ‘n funksie van verskeie parameters soos onder andere die goud konentrasie in oplossing, PSMI massa, kontak tyd en ‘n mengings tempo. Die [AuCl4]- ekstraksie gebeur met ‘n geweldige sorpsie kinetika en is afhanklik van die mengings tempo gedurende die stel sorpsie proses. Die gefunksionaliseerde PSMI nanopartikels het ‘n maksimum goud sorpsie kapsiteit van 1.76 mmol/g (347.7 mg/g). Langmuir en Freundlich isoterm modelle was gepas en geanaliseer op die experimentele sorpsie data waarvan die Langmuir isoterm model die data die beste gepas het. De-sorpsie effektiwiteit van ongeveer 80 % en 93% was vekry vir die aangesuurde thiourea (0.25 M thiourea/2 M HCl) en ‘n mengsel van 10 M HNO3/0.5 M HCl as elueer oplossings, onderskeidelik. X-straal foto-elektron spektroskopie (XPS) analiese bevestig ongetwydeld die geimmobileerde goud spesies in oksidasietoestande van 0, +I, en +III op die PSMI nanopartikels. Hierdie is bewyse dat die [AuCl4]- oorspronklik teenwoordig in die goud oplossings is onderhewe auto-reduksie fenomeen op die oppervlak van die gefunksionalieerde PSMI nanopartikels. Die bestaan van verskeie goud spesies dra by tot die power de-sorpsie effektiwiteit van ge-immobiliseerde goud. Bykomend tot die nanopartikels is mikro- tot millimeter grootte PSMI partikels voorberei met ‘n elektro-sproei proses. Hierdie metode stel ons instaat om ‘n wye reeks sferiese en quasi-sferiese PSMI partikel se deersnee voorteberei. Deur die manupulasie van die eksperimentele kondisies gedurende die elektro-sproei proses, soos die konsentrasie van die PSMI in oplossing, die kapilêre punt-tot-ontvanger afstant, vloeispoed en die toegepasde potensiaal. 13C KMR en FTIR spectroskopiese analiese wys dat die elektro-sproei proses die PSMI partikel bereiding toelaat sonder enige veranderinge in die chemiese samestelling van die PSMI materiaal. Oppervlak area en porie-grootte analise wys dat 450lksdfhld en dskl jmm partikels gebruik in die goud ekstraksie eksperimente is mikro-porieës en het spesifieke oppervlak-areas van 2.8 ± 0.4 m2/g en 2.0 ± 0.1 m2/g onderskeidelik. Mikro- tot millimeter grootte poli(stireen-ko-maleimied) (PSMI) partikels van 450 μm en 1620 μm deursnee was getoets as potensieele anion-uitruilings-hars vir die ekstraksie van [AuCl4]- vanuit suur oplossings. Die tyd afhanklike studies gee aanduiding dat die mate van goud opname toeneem met ‘n toename in kontak-tyd en is afhanklik van die goud konsentrasie in die [AuCl4]- oplossings. ‘n Maksimum opname-kapasiteit van 120.7 mg/g en 98.2 mg/g was verkry vir die 450 μm en 1620 μm hars partikels onderskeidelik. Die eksperimentele sorpsie-data volg ‘n lineêre neiging in ooreenstemming met die Freundlich model. Die sorpsie neiging van [AuCl4]- dui aan dat ‘n meervuldige laag sorpsie proses domineer. De-sorpsie van die geimobiliseerde goud spesies vanaf die PSMI hars partikels was bestudeer deur gebruik te maak van verskeie elueermiddels soos HCl, HNO3, thiourea, NaCN en NaOH oplossings. Die beste resultate is verkry deur ‘n mengsel te gebruik van 10M HNO3/0.5M HCl as elueermiddel met n de-sorpsie effektiviteit van ongeveer 97%. Superparamagnetiese magnetiet (Fe3O4) nanopartikels met ‘n hoë graad van kristaliniteit en fase-reinheid was voorberei deur ‘n chemiese ko-neerslagvorming van Fe2+ en Fe3+ soute. Die gemiddelde deursnee van die Fe3O4 nanopartikels was ongeveer 7 – 8 nm. Die Fe3O4 nanopartikels was omhul met oleic suur benatter molekules wat gebruik word as saadjies vir voorbereiding van 50 nm deursnee-magnetiese PSMI nanopartikels deur middel van ‘n imidisasie reaksie. TEM analiese bevestig dat die magnetiese PSMI partikels nanopartikels bestaan uit ‘n magnetiet-kern polimeer-skil struktuur.

This thesis considers methods which can be employed to increase the mass of copper transferred into and out of the organic phase during the load and strip stages of commercial solvent extraction processes. Conventional 5-alkylsalicylaldoxime reagents transfer 1 mol of divalent copper per 2 mol of ligand in a neutral complex of the type [Cu(L-H)2] via a pH-swing process. New triacidic ligands have been designed which triple the molar transport of copper to form [Cu3(L-3H)2]. Until recently copper recovery by solvent extraction has been confined to oxidic ores which are leached with sulfuric acid. New leaching technologies generate high tenor copper sulfate feed streams from sulfidic ores. The conventional 5- alkylsalicylaldoxime reagents do not work effectively in conjunction with these leach processes as they do not consume the acid which is generated on loading the oxime. To address this problem ditopic zwitterionic ligands have been designed which can transfer both metal cation and attendant anion. These new metal salt reagents are diacidic, therefore not only transfer metal salts but also increase the molar transport relative to the conventional reagents. Equilibrium-modifiers are often added to improve the mass transport efficiency of conventional solvent extraction processes. The nature of their interaction with the species in solution is poorly understood. This thesis investigates their interaction with the free ligands and copper complexes to gain an understanding of their mode of action in order to rationalise the design of future modifiers to optimise recovery efficiencies. Increased molar transport is addressed in Chapter 2. The diacidic ligand 5- methylsalicylaldehyde-pivaloylhydrazide (L2) and its dinuclear copper complex [Cu2(L2-2H)2] were synthesised and characterised to gain an understanding of their speciation in solution. X-ray structural analysis of [Cu2(L2-2H)2] confirmed that the phenolate oxygen atoms bridge the copper centres rather than the amidato oxygen atoms of the hydrazone. Variable temperature magnetic susceptibility data confirm that the copper centres are antiferromagnetically coupled as expected for the Cu-OCu angle (99.6(2)°). An understanding of the coordination geometry of the dinuclear systems lead to design of triacidic ligands. A series of 3-hydrazono- and 3- hydroxyanil- 5-alkylsalicylic acids were synthesised. The prototype ligand 5-methyl 3-octanoylhydrazonosalicylic acid (L6) was demonstrated to triple molar transport and increase mass transport by 2.5 fold. Solvent extraction results indicate that copper is sequentially loaded as pH is increased. The plateaux observed in loading curves suggest formation of stable mono-, di-, and tri-nuclear copper complexes within the pH-ranges 1.75 - 2.75, 3.25 - 4.0 and > 4.25 respectively. The triacidic ligands were also demonstrated to double the molar transport of the conventional salicylaldoximes when used in 1:1 blends by formation of a ternary complex. Chapter 3 describes the incorporation of two tertiary amine groups into diacidic salicylaldehydehydrazone ligands to form dinucleating metal salt extractants. Piperidinomethyl, piperazinomethyl and dihexylamino groups were incorporated into various positions of the ligand including 3- and/or 5- positions of the salicylaldehyde or incorporated into the hydrazone. Solvent extraction results obtained for 3,5- bis((dihexylamino)methyl)salicylaldehyde-octanoic hydrazone (L20) are consistent with transfer of 1 mol of copper sulfate per mol of ligand in the organic phase between pH 2.0 and 2.5. This result is indicative of the formation of [Cu2(L20)2(SO4)2]. Conventional salicylaldoximes are “strong” copper extractants which require concentrated acid electrolyte to efficiently strip the copper from the organic phase. However, as the use of concentrated acid affects the quality of the copper cathodes, oxygen-containing equilibrium modifiers are often added. These facilitate copper stripping without adversely affecting the loading. The affect of 2-ethylhexanol (2- EH) and trioctylphosphine oxide (TOPO) on the extractive ability of 5-toctylsalicylaldoxime (19) in n-heptane is reported. Both are found to decrease copper extraction more under stripping conditions than loading conditions. 2-EH shows little affect at pH greater than 2.5. TOPO does not significantly affect copper loading at pH greater than 3.0. Evidence for the formation of the adduct [Cu(19-H)2)(TOPO)] was obtained from UV/Vis, IR, EPR and sonic spray mass spectrometry.

In the design of a solvent extraction plant for metals it is necessary to treat the equilibrium data either graphically or analytically. This enables stagewise calculations to be performed to explore solvent usage and feed conditions and so optimise on the cost of recovery of the metal. The present study reviews the methods of presenting and correlating equilibrium data for solvent extraction systems involving metals; the limitations of each approach are highlighted. The most important example of metal extraction which has been studied falls into that class involving a metal species, in acid aqueous media, which displaces protons from the organic extractant during the mass transfer process. In the typical case of copper extracted by hydroxyoximes the equilibrium problem reduces to one of modelling a surface. The concentration of copper in the organic phase is a function of the concentrations of copper and sulphuric acid in the aqueous phase. Empirical models seem to be as satisfactory to the engineer as chemical ones provided the model is used between restricted regions of data. Practical work has involved the measurement of equilibrium data for the extraction of zinc and copper by di- (2-ethylhexyl) phosphoric acid (D2EHPA) in a kerosene diluent. Both the single and binary metal systems have been studied. The data reported are for feeds between 2-40 g/l zinc, 2-60 g/l copper and 20% V/v D2EHPA. A limited number of results are also presented for 10% V/v D2EHPA. Specific chemical and empirical models have been developed to correlate these data. Because the extractant has a high affinity for zinc in the presence of copper the binary data can be modelled making the assumption that the interaction of copper on zinc is negligible. However the effect of zinc on the limited extraction of copper is significant, the zinc reducing the copper loading markedly. In this way zinc can be decontaminated of copper. The methods for presentation of equilibrium data are discussed and a computer program is given which displays three dimensional equilibrium surfaces. Classical design procedures for stagewise. calculations are used against these three dimensional data plots. Computer programs which allow the investigation of a variety of operating conditions have also been written.

A extração de complexos aniônicos pelas aminas de cadeias longas oferece muitas possibilidades ao químico analista. Muitas aplicações já são de uso corrente e muitas outras são potencialmente previstas para diversas áreas, incluindo-se hidrometalurgia, química de produtos de fissão, química dos metais de transição, dos elementos do grupo da platina, dos actnídeos e dos lantanídeos, recuperação e descontaminação na disposição de resíduos. Ênfase especial é dada à química do urânio e do tório, para os quais já são incluídas aplicações de caráter industrial. Neste trabalho é descrito o comportamento de extração de U, Fe, Cd, In, Zn, Cu, Co, Ni, Mn, Cr, Ag, Bi, Pb, Tl, Ru, Rh, Pd, Pt, Ir, Os, Au, Hg, Sn e Sb com tri-n-octilamina diluída em benzeno, xileno, varsol e metil-isobutil-cetona em meio clorídrico. Para alguns destes elementos foi estudada a extração também em meios HNO3, H2SO4 e HI. Foi estudado o efeito de tiouréia como complexante, formando espécies catiônicas com vários elementos e suas consequências na extração. Foi estudado também o efeito do tratamento da fase orgânica contendo o elemento extraído, pos soluções ácidas de tiouréia. O trabalho demonstra que para os elemento cujos complexos com a tiouréia são fortes, como prata, tálio-III, mercúrio, cobre, ouro, paládio, platina e rutênio, a extração é fortemente reprimida. Para complexos de fôrça intermediária, como chumbo, antimônio e tálio-I, a tiouréia não impede a extração total, mas esta é parcialmente reprimida. Para elementos que formam complexos fracos com a tiouréia, êstes são rompidos e o elemento é totalmente extraído pela amina, como é exemplo o cádmio, formando um complexo {Cd(tu)}++ fraco, mas bem extraído em meio HCl pela amina. Êste impedimento de extração através da complexação com tiouréia na fase aquosa, para vários elementos, ou a sua reextração da fase orgânica pela ação de tiouréia, vem contribuir para um melhor entendimento do mecanismo de extração com aminas de cadeia longa. Ficou evidenciado que os complexos estáveis, de natureza catiônica, formados entre tiouréia e vários elementos, não são extraídos pela amina. Isso vem confirmar o mecanismo, aceito pela maioria dos autores, de que a extração pelas aminas de alto PM é uma associação de íons entre a amina protonada e as espécies aniônicas extraídas, isto é, uma reação de troca aniônica. Êste mecanismo foi comprovado uma vez mais através de experiências de troca iônica com resinas catiônica e aniônica. Espécies clorocomplexas aniônicas de Ag-I, Hg-II e CU-II em meio HCl são fortemente fixadas em resina aniônica na forma R-Cl e totalmente eluídas por soluções HCl-tiouréia. Estas soluções clorídricas de Ag-I, CU-II e Hg-II percoladas em coluna de resina catiônica mostraram que não houve nenhuma retenção dêstes elementos. Estas experiências, repetidas após a adição de tiouréia, mostraram que os complexos formados com tiouréia são totalmente retidos pela resina catiônica. O uso de tiouréia aumentou consideravelmente a seletividade na extração e na reextração de vários elementos com tri-n-octilamina. É dada ênfase especial à extração de urânio e sua descontaminação de vários elementos que o acompanham. Como resultado dêstes estudos é apresentado um método para a determinação espectrofotométrica de urânio diretamente na fase orgânica tri-n-octilamina-benzeno. O método não é o mais sensível, mas apresenta alta seletividade quando o urânio é extraído em meio HCl na presença de tiouréia. O trabalho descreve ainda várias outras aplicações da técnica proposta, como a preparação de chumbo-212, bismuto-212 e tálio-208, extraídos de cloreto de tório por TOA-benzeno, a separação de índio-115m do seu radioisótopo gerador, cádmio-115, bem como diversos esquemas para a separação de vários elementos entre sí. Uma contribuição importante é dada à química do rutênio, facilitando sua separação em misturas de produtos de fissão de difícil resolução e nas separações rutênio-bismuto, rutênio-tório e rutênio-urânio. O aproveitamento de urânio e plutônio em soluções provenientes da dissolução de elementos combustíveis queimados envolve a separação dos produtos de fissão, entre êles o rutênio, que apresenta sérias dificuldades, tendendo sempre a acompanhar o urânio na fase orgânica usada para a sua separação (fosfato de n-tributilo e aminas). A complexação do rutênio com tiouréia permite uma extração de urânio e plutônio mais seletiva, retendo o rutênio na fase aquosa. Várias outras aplicações são indicadas para os elementos do grupo da platina, prata, mercúrio, e ouro, cádmio, índio e zinco. Interessantes observações são feitas quanto à cinética de formação do complexo ferro-tiouréia (lenta), possibilitando separações dêste elemento de vários outros cuja cinética é mais rápida, bem como à cinética de reextração de paládio com tiouréia em meio ácido. / Abstract not available.

O níquel e o cobalto são dois metais de ampla utilização na indústria mundial, principalmente na produção de aços inoxidáveis e ligas metálicas no caso do níquel, e baterias e superligas no caso do cobalto; estes dois metais são encontrados associados na natureza, cerca de 55% da produção mundial de cobalto é derivada da mineração de níquel. Porém, devido a estes elementos apresentarem comportamento químico similar em soluções aquosas, a sua purificação se torna difícil, impulsionando pesquisas voltadas para o melhoramento dos processos existentes para este fim. Dentre estes processos podemos citar a extração por solventes, e para um melhor entendimento da purificação de níquel e cobalto a partir dessa técnica, foi realizado esse estudo, o qual tem como objetivo estudar os complexos organometálicos formados na etapa de extração. A fase aquosa utilizada para a realização deste estudo é um licor sintético de lixiviação que contém níquel, cobalto, manganês, cobre, magnésio e cálcio na sua composição química. Por outro lado, a fase orgânica foi preparada com os extratantes ácidos Cyanex 272, Versatic 10 e D2EHPA de forma individual, assim como as suas misturas, como são: [Cy15-Ve5], [Cy10-Ve10], [Cy5-Ve15], [Cy15-DH5], [Cy10-DH10], [Cy5-DH15], [Ve15-DH5], [Ve10-DH10] e [Ve5-DH15]. Com o intuito de compreender a interação entre o extratante e o íon metálico (complexo organometálico), foi determinada a estequiometria dos complexos através dos métodos de análises da inclinação e o método da variação contínua (método de Job) e a caracterização foi feita utilizando as técnicas de espectrofotometria UV-Vis, espectroscopia FT-IR e termogravimetria (TG/DTG/DSC). Através dos resultados obtidos nos ensaios de extração, foram escolhidos os sistemas, [Cy15-Ve5] e [Cy10-DH10] para realizar o estudo dos complexos organometálicos. O método da variação contínua mostrou a participação de duas moléculas de extratante na complexação de cobalto em todas as fases orgânicas estudadas, com exceção do Versatic 10, a qual apresentou o envolvimento de 5 moléculas. Na complexação de níquel, foram encontradas uma molécula com D2EHPA e [Cy10-DH10], duas moléculas com Cyanex 272 e [Cy15-Ve5] e três moléculas com Versatic 10. As análises por UV-Vis forneceram o número de coordenação dos complexos organometálicos de níquel e cobalto formados tanto na solução aquosa como nas diferentes fases orgânicas estudadas. Através destes resultados determinou-se que o níquel apresentou uma simetria octaédrica nas condições testadas (fase aquosa e fases orgânicas), já o cobalto apresentou uma simetria octaédrica na solução aquosa e no Versatic 10, e simetria tetraédrica nas outras condições (Cyanex 272, D2EHPA e mistura dos extratantes). Por outro lado, as análises de infravermelho (FT-IR) mostraram que a extração do íon metálico é realizada através do mecanismo de troca catiônica (substituição do hidrogênio da ligação P-O-H). As análises termogravimétricas forneceram as temperaturas de decomposição dos complexos e, a presença ou não de moléculas de água no mesmo. Através destes resultados foi confirmado que os complexos de níquel se tratam de complexos hidratados, com exceção do complexo [Ni-Versatic 10], o qual corresponde a um complexo desidratado. Entretanto, os complexos organometálicos formados com o cobalto, são complexos desidratados, ou seja, que os sítios de coordenação estão completamente preenchidos por moléculas de extratante. / Nickel and cobalt are two metals widely used in the world industry, mainly in the production of stainless steel like an alloy element in the case of nickel, and both batteries and super alloys in the case of cobalt. These metals are found associated in nature and about 55% world production of cobalt is derived from the nickel mining. Due their similar chemical behavior in aqueous solution, its purification becomes difficult, encouraging research to improve the current processes, such as, the solvent extraction. In order to have a better understanding about both nickel and cobalt purification through this technique, this study has been carried out to evaluate the organometallic complexes formed during the extraction stage. The aqueous phase used in this study is a synthetic leach liquor containing in its chemical composition nickel, cobalt, manganese, copper, magnesium and calcium. On the other hand, the organic phase was prepared using the acidic extractants, as such: Cyanex 272, Versatic 10 and D2EHPA, as well as their mixtures [Cy15 Ve5], [Cy10-Ve10], [Cy5 Ve15], [Cy15-DH5], [Cy10-DH10], [Cy5 DH15], [Ve15-DH5], [Ve10-DH10] and [Ve5-DH15]. In order to understand the interaction between extractant molecule and metal ion (organometallic complex), the complex stoichiometry was determinate through two methods, such as: slope analysis and the continuous variation (Job´s method). Furthermore, the complex characterization was carried out using some techniques, spectrophotometry UV Vis, spectroscopy FT-IR and thermogravimetry (TG/DTG/DSC). The systems [Cy15-Ve5] and [Cy10-DH10] have been chosen in order to study the organometallic complexes formed. The continuous variation method has shown the participation of two extractant molecules in the complexation of cobalt in all organic phases studied in this work, except for the Versatic 10, where was observed the involvement of 5 molecules to form the complex. On the other hand, to form the nickel complex, when the D2EHPA and [Cy10-DH10] were used, five molecules were involved in the complex formation process. Furthermore, two molecules are present in the complex if Cyanex 272 or [Cy15-Ve5] are used like extractant and, when the Versatic 10 is used, three molecules are necessary to form the organometallic complex. The UV-Vis analysis provided the coordination number of the organometallic complexes of nickel and cobalt formed in both the aqueous and all organic phases chosen. It was determined that nickel showed an octahedral symmetry in both aqueous phase and organic phases, whereas the cobalt exhibited an octahedral symmetry both the aqueous solution and Versatic 10, and a tetrahedral symmetry in the other conditions (Cyanex 272, D2EHPA and extractants mixtures). Moreover, the infrared (FT-IR) analysis showed that the metal ion extraction is performed through the cation exchange mechanism (hydrogen substitution of P-O-H bond). Lastly, the thermogravimetric analysis provided the complexes decomposition temperatures and the presence or absence of water molecules. It was confirmed that nickel complexes are hydrated, except for the [Ni-Versatic 10] complex, which corresponds to a dehydrated complex. However, all organometallic complexes with cobalt are dehydrated complexes, that is, coordination sites are completely filled with extractant molecules.