The bulk of the world's known nickel reserves are contained in laterite ores but sulphidic ores remain the main source of the Western world's nickel production. With the continuing increase in nickel consumption and the depletion of sulphidic ores, the traditional source of nickel, the extraction of nickel from lateritic ores has been the subject of research interest worldwide. Advances in pressure acid leaching (PAL) technology have resulted in significant commercial attempts to extract nickel from these ores. Leaching the ore with sulphuric acid at elevated temperatures and pressures allows almost complete dissolution of the nickel and cobalt, a valuable byproduct of these ores, but yields highly contaminated pregnant leach solutions. Separating and purifying the nickel and cobalt from these solutions remains a hindrance to full commercial production. Several purifying techniques have been commercialised but all suffer from continuing technical problems. Among them, however, the direct solvent extraction (DSX) technique offers several advantages. Direct solvent extraction involves the separation of the nickel and cobalt directly from the partially neutralised pregnant liquor stream (PLS) by solvent extraction with Cyanex(R) 272 as the extractant. However certain contaminants adversely affect the solvent extraction process. Among them is chromium and little is known about the solvent extraction behaviour of this metal. The present work investigated the solvent extraction of chromium with Cyanex(R) 272. It was found that the solvent extraction behaviour of chromium(III) and chromium(VI), both of which could be found in PAL-generated PLS, are distinctly different. / For chromium(III), solvent extraction tests showed that (a) it is extracted in the pH range 4-7; (b) the extraction is partly influenced by diffusion; (c) the apparent equilibration time is significantly longer than most transition metals; (d) increases in temperature from 22 to 40 C resulted in increases in the extraction; (e) the pH0.5 increases in the order nitrate < chloride < sulphate in the presence of these anions; (f) the presence of acetate depresses extraction of chromium(III) when the solution is allowed to stand before extraction; (g) in the PLS, chromium(III) precipitated at lower pH than that predicted by the solubility product principle; and (h) the pH0.5 decreases as the Cyanex(R) 272 concentration increases. Chromium(III) is initially extracted by solvation of its inner sphere complex, which then undergoes further reaction in the organic phase leading to the formation of a much more stable species that is difficult to strip. A reaction scheme together with a description of both the initially extracted and resulting stable species is proposed. Extraction of chromium(VI), on the other hand, (a) occurs at pH less than 2 by solvation of chromic acid; (b) is independent of the aqueous phase composition; (c) does not occur in the pH range (3-6) used in the separation of nickel and cobalt. The latter is irrespective of temperature up to 40 C, the use of industrial PLS as the aqueous phase or the presence of an anti-oxidant in the organic phase. The stripping of chromium(III) from a loaded organic phase can be achieved using 1-4 mol L-1 mineral acids provided the stable organic species have not formed making industrial scale stripping of chromium(III) from Cyanex(R) 272 difficult. The exact composition of the aqueous phase during extraction affects the stripping efficiency.

O minério limonítico de níquel é considerado uma fonte de níquel e cobalto a partir de mineração. No entanto, o minério é heterogêneo e a concentração dos metais varia conforme a localização. Sendo assim, é necessário o desenvolvimento de uma metodologia que permita determinar os parâmetros de operação de um processo de separação de metais levando em consideração a composição de cada minério. No processo hidrometalúrgico, diversas técnicas de purificação ou separação dos metais podem ser usadas. O presente trabalho estudou o uso da extração por solventes para tratar o licor baseado no lixiviado de minério limonítico de níquel. No processo de extração por solventes foram determinados os parâmetros de extração dos metais como: pH, concentração do extratante na fase orgânica e diluído em querosene, relação entre as fases aquosa e orgânica (A/O) e número de contatos contracorrente teóricos para extração do metal. A extração de 100% do ferro utilizando Cyanex 272 foi determinada em pH 2, concentração do extratante 25% em volume diluído em querosene, relação A/O 1/3 e três contatos contracorrente. Durante a extração do ferro também houve coextração de 27% do cobalto. Foi possível recuperar o cobre da solução através da extração utilizando Acorga M5640 em pH 2, concentração do extratante na fase orgânica igual 5% v/v, relação entre as fases 1/1 e um contato contracorrente. O alumínio e o zinco foram extraídos em pH 3,5, utilizado Cyanex 272 como extratante na concentração 25% em volume, relação A/O 1/2 e dois contatos contracorrente. A fim de obter uma solução aquosa contendo apenas níquel em solução, a última etapa foi a remoção dos metais remanescentes na solução (cobalto, cromo, magnésio e manganês) utilizando Cyanex 272. O pH para essa extração foi 5, a concentração do extratante 20% v/v, relação entre as fases 1/1 e cinco contatos contracorrente. Ao final, foi possível obter uma solução aquosa contendo níquel em solução na concentração 2,52g/L, o que corresponde a 100% do níquel presente na solução sintética. Além do níquel, 0,19 g/L de magnésio e 0,008g/L de cromo permaneceram na solução final. / Nickel limonite ore is a source of nickel and cobalt. However, the ore is heterogeneous and concentration changes according the location of the ore. Therefore, determination of the operating parameters is required to separate the metals taking into account the composition of these ores. Hydrometallurgical process is used to treat leach liquor from ores. This work studied the treatment of synthetic solution based on leach liquor of nickel limonite ore by solvent extraction. During the study was determinated the metals extraction parameters as pH, extractant concentration in the organic phase, aqueous and organic ratio (A/O) and number of theoretical extraction stages. The extraction of iron was 100% using Cyanex 272 at pH 2, extractant concentration 25% (v/v) and three extraction stages at an A/O ratio 1/3. Nevertheless, during the extraction of iron, cobalt was co-extracted. The cobalt lost was 27% at the parameters used to extract. It was possible to recover copper from the synthetic solution using Acorga M5640 as extractant at pH 2, extractant concentration 5% v/v, one extraction stage and an A/O ratio 1/1. Aluminium and zinc were removed from synthetic solution at pH 3.5, organic phase with 25% v/v of Cyanex 272 and two extraction stages at an A/O ratio 1/2. The last part of work was removed cobalt, chromium, magnesium and manganese from the aqueous solution. The reason is staying just nickel in the final solution. Cyanex 272 at pH 5 and 20% v/v concentration was used and five extraction stages and an A/O ratio 1/1 was necessary to extract the metals. The finally solution was composed by 2.52g/L of nickel, corresponding 100% of nickel from synthetic leach liquor of nickel limonite ore. In addition, 0.19g/L of magnesium and 0.008g/L of chromium staying at solution.

O minério limonítico de níquel é considerado uma fonte de níquel e cobalto a partir de mineração. No entanto, o minério é heterogêneo e a concentração dos metais varia conforme a localização. Sendo assim, é necessário o desenvolvimento de uma metodologia que permita determinar os parâmetros de operação de um processo de separação de metais levando em consideração a composição de cada minério. No processo hidrometalúrgico, diversas técnicas de purificação ou separação dos metais podem ser usadas. O presente trabalho estudou o uso da extração por solventes para tratar o licor baseado no lixiviado de minério limonítico de níquel. No processo de extração por solventes foram determinados os parâmetros de extração dos metais como: pH, concentração do extratante na fase orgânica e diluído em querosene, relação entre as fases aquosa e orgânica (A/O) e número de contatos contracorrente teóricos para extração do metal. A extração de 100% do ferro utilizando Cyanex 272 foi determinada em pH 2, concentração do extratante 25% em volume diluído em querosene, relação A/O 1/3 e três contatos contracorrente. Durante a extração do ferro também houve coextração de 27% do cobalto. Foi possível recuperar o cobre da solução através da extração utilizando Acorga M5640 em pH 2, concentração do extratante na fase orgânica igual 5% v/v, relação entre as fases 1/1 e um contato contracorrente. O alumínio e o zinco foram extraídos em pH 3,5, utilizado Cyanex 272 como extratante na concentração 25% em volume, relação A/O 1/2 e dois contatos contracorrente. A fim de obter uma solução aquosa contendo apenas níquel em solução, a última etapa foi a remoção dos metais remanescentes na solução (cobalto, cromo, magnésio e manganês) utilizando Cyanex 272. O pH para essa extração foi 5, a concentração do extratante 20% v/v, relação entre as fases 1/1 e cinco contatos contracorrente. Ao final, foi possível obter uma solução aquosa contendo níquel em solução na concentração 2,52g/L, o que corresponde a 100% do níquel presente na solução sintética. Além do níquel, 0,19 g/L de magnésio e 0,008g/L de cromo permaneceram na solução final. / Nickel limonite ore is a source of nickel and cobalt. However, the ore is heterogeneous and concentration changes according the location of the ore. Therefore, determination of the operating parameters is required to separate the metals taking into account the composition of these ores. Hydrometallurgical process is used to treat leach liquor from ores. This work studied the treatment of synthetic solution based on leach liquor of nickel limonite ore by solvent extraction. During the study was determinated the metals extraction parameters as pH, extractant concentration in the organic phase, aqueous and organic ratio (A/O) and number of theoretical extraction stages. The extraction of iron was 100% using Cyanex 272 at pH 2, extractant concentration 25% (v/v) and three extraction stages at an A/O ratio 1/3. Nevertheless, during the extraction of iron, cobalt was co-extracted. The cobalt lost was 27% at the parameters used to extract. It was possible to recover copper from the synthetic solution using Acorga M5640 as extractant at pH 2, extractant concentration 5% v/v, one extraction stage and an A/O ratio 1/1. Aluminium and zinc were removed from synthetic solution at pH 3.5, organic phase with 25% v/v of Cyanex 272 and two extraction stages at an A/O ratio 1/2. The last part of work was removed cobalt, chromium, magnesium and manganese from the aqueous solution. The reason is staying just nickel in the final solution. Cyanex 272 at pH 5 and 20% v/v concentration was used and five extraction stages and an A/O ratio 1/1 was necessary to extract the metals. The finally solution was composed by 2.52g/L of nickel, corresponding 100% of nickel from synthetic leach liquor of nickel limonite ore. In addition, 0.19g/L of magnesium and 0.008g/L of chromium staying at solution.

This project aimed to examine the separation of cobalt and nickel using solvent extraction (SX) with the extractant CYANEX 272 (C272). It was intended to investigate the Co-Ni separation in a sulphate-based leach solution in presence of other contaminants. This is an area of interest because of the difficulty of separating metals of similar properties within the field of hydrometallurgy.  Batch tests, with varying modifiers and diluents, were carried out to examine the effect of organic phase composition on phase separation. The effect of pH on equilibrium was investigated by constructing equilibrium curves. Through various shaking tests, different separation parameters were studied. McCabe-Thiele diagrams were constructed to predict design parameters. In order to simulate a continuous 3-stage countercurrent solvent extraction, batch tests were performed. Scrubbing, as means of impurity removal was also investigated. Finally, the product’s purity was examined by the help of crystallization.  The organic feed mixture that resulted in a sufficient phase separation consisted of C272, tributyl phosphate and naphtha. At pH 4, equilibrium curves showed that equilibrium was either not reached or affected by competing metal ions. A standard equilibrium curve appearance was seen at pH 4.5, resulting in that the theoretical required stages for extraction was calculated to 3 stages (A/O=1). However, a McCabe-Thiele diagram did not give an accurate representation of the more complex case (presence of contaminants). Batch simulation results gave a cobalt recovery of 69% and 100% at pH 4.5 and 4.8, and a nickel recovery of 0% and 3%, respectively. A recommended pH-value for solvent extraction could not be stated, because the choice must be based on operation specifications. Therefore, several different aspects (Co recovery, purity, and economical etc.), must be accounted for. A similar pH-trend was shown in scrubbing, where an increase of pH resulted in an increase of metal ions’ organic concentration. For stripping, acid test results proved 24 g/L sulphuric acid to give the highest cobalt concentration, with a marginal difference in concentration of impurities. An overview of the entire SX process, indicated that extraction, scrubbing, and stripping were all successful operations. The extraction stage showed a Co and Ni recovery of 99% and 0.02%, respectively, and a separation factor of 14250. Distribution results indicated that Al was difficult to remove and was transferred with Co into the product. Therefore, this element must be removed before SX. From noticing an increase of Co:Ni ratio throughout the process, solvent extraction was considered an effective separation method for cobalt and nickel separation. A considerably high purity of cobalt sulphate was produced. However, impurities Al and Ca were also detected in the product. Increasing the acetone volume in crystallization resulted in an increase of Co purity. An increase of the cobalt sulphate crystals formed was observed when increasing the acetone volume, where no impurities were detected.