What is it about?
Separation of Co(II) and Li(I) by non-dispersive solvent extraction using a hollow fiber supported liquid membrane has been investigated. Separation of both the metals by flat sheet supported liquid membrane and dispersive solvent extraction technique has also been investigated and compared. The parameters for the three processes were optimized to achieve quantitative separation of Co(II) over Li(I) with Cyanex 272 diluted with kerosene. The feasibility to produce pure metal salt solutions was established by controlling the process parameters like pH of the feed solution, extractant concentration, metal ion concentration and acid concentration for selective stripping. For both the hollow fiber and the flat sheet supported liquid membrane processes, the aqueous feed pH of 6.0 and 750 mol/m3 of Cyanex 272 in the membrane phase were the best conditions for extraction, whereas the best stripping results were obtained with 100 mol/m3 and 25 mol/m3 H2SO4, respectively. In the case of dispersive solvent extraction process, the quantitative separation of the metals was achieved by extraction at equilibrium pH of 5.50 using 100 mol/m3 of Cyanex 272, and stripping with 10 mol/m3 H2SO4 solution. Under the optimum conditions, the separation factor was found to be 18, 178 and 180 for hollow fiber supported liquid membrane, flat sheet supported liquid membrane, and dispersive solvent extraction, respectively. Suitable mathematical models for the quantitative extraction of the metal in dispersive solvent extraction and mass-transfer coefficient in non-dispersive solvent extraction were proposed and validity of the models was verified. Proposed models and the mathematical analyses revealed that both dispersive solvent extraction and non-dispersive solvent extraction process followed cation-exchange reaction mechanism with similar kind of stoichiometry.
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Why is it important?
Highlights Co/Li separation by hollow fiber supported liquid membrane using Cyanex 272 studied. Dispersive/non-dispersive solvent extraction process is compared for Co/Li separation. Suitable models are proposed and validity of models is analyzed for both the system. Reaction mechanism and stoichiometry involved are analyzed for all the processes.
Perspectives
Separation of Co (II) and Li(I) by HFSLM has reasonable similarity with FSSLM and NDX, and make the HFSLM process a better candidate, which can overcome the shortcomings of both the processes. Both NDSX and DSX processes follow a similar kind of chemical reaction mechanism and stoichiometry. Usually, two moles of Cyanex 272 are involved to extract one mole of Co(II) both in DSX and NDSX processes. The DSX process is an equilibrium pH controlled and NDSX is a non-equilibrium pH controlled process. At the optimum conditions the separation factors follow the order FSSLM ≥ DSX > HFSLM. A complete separation of both the metals with 99.99 % purity can be achieved by HFSLM process using Cyanex 272 as a mobile carrier, which can replace the FSSLM and NDX processes successfully. Both NDSX and NDX processes can compete each other for quantitative separation with required purity, controlling important process parameters like pH of feed solution, extractant concentration, metal ion concentration and selective strip acid concentration. An interesting relationship between equilibrium constant of DSX and mass transfer coefficient of NDSX has been established and their validity analysed through the proposed model. The models such as modified exponential equations and quadratic equations could be a predictive tool for the extraction/separation of Co(II) and Li(I) within 95% confidence interval. As HFSLM provides higher surface area, it is feasible to design a high volume reactor and achieve quantitative extraction with requisite purity. The reusability of the membrane module and zero discharge of effluent in the case of HFSLM can be a promising green technology over traditional DSX and FSSLM processes. Under the optimum conditions, selective metal enrichment from the dilute industrial waste or dilute leach liquors can be achieved by controlling the strip acid concentration in HFSLM process.
Dr Basudev Swain
Institute for Advanced Engineering (IAE)
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This page is a summary of: Separation of Co(II) and Li(I) with Cyanex 272 using hollow fiber supported liquid membrane: A comparison with flat sheet supported liquid membrane and dispersive solvent extraction process, Chemical Engineering Journal, July 2015, Elsevier,
DOI: 10.1016/j.cej.2015.02.040.
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