Developing a solvent extraction process for the separation of cobalt and iron from nickel sulphate solutions

Olivier, Michiel Casparus (Stellenbosch : Stellenbosch University, 2011-12)

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/17984
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