Comparison of liquid–liquid extraction of Cr(VI) from acidic and alkaline solutions by two different amine extractants

The extraction of hexavalent chromium, Cr(VI), was performed from acidic sulphate and alkaline carbonate media by using Aliquat 336 and Alamine 336 extractants in kerosene under different experimental conditions. The optimum conditions for extraction of Cr(VI) were evaluated by varying the experimental parameters. On the basis of the slope analysis data, the composition of the extracted species was found to be R4NHCrO4¯ for Aliquat 336 and R3NH2CrO4¯ for Alamine 336 in acidic medium and (R4N)2CrO4¯ for Aliquat 336 in alkaline medium. The results of the effect of temperature on the equilibrium extraction constant value clarify that the extraction is an endothermic process for the extraction by Aliquat 336 and Alamine 336 in acidic and alkaline media. 1 M NaOH as strippant completely strip Cr(VI) from the loaded extractants from acidic medium, in one step. In alkaline medium good stripping of Cr(VI) can be achieved from loaded extractants using 1 M NaOH in two steps. The results indicate that extraction of Cr(VI) from acidic media is more favored than from alkaline solution. The liquid–liquid extraction method was applied for the removal and recovery of Cr(VI) from electroplating waste solution.