Abstract
This study investigates the separation of two heavy metals, Cd(II) and Cu(II), from the mixed synthetic feed using a liquid-liquid extraction. The current study uses tri-octyl methylammonium chloride (Aliquat 336) as the extractant (with tributyl phosphate (TBP) as a phase modifier), diluted in toluene, in order to investigate the selective extraction of Cd(II) over Cu(II) ions. We investigate the use of ethylenediaminetetraacetic acid (EDTA) as a masking agent for Cu(II), when added in aqueous feed, for the selective extraction of Cd(II). Five factors that influence the selective extraction of Cd(II) over Cu(II) (the equilibrium pH (pHeq), Aliquat 336 concentration (Aliquat 336), TBP concentration (TBP), EDTA concentration (EDTA), and organic to aqueous ratio (O:A)) were analyzed. Results from a 25–1 fractional factorial design show that Aliquat 336 significantly influenced Cd(II) extraction, whereas EDTA was statistically significant for the antagonistic effect on the E% of Cu(II) in the same system. Moreover, results from optimization experiment showed that the optimum conditions are Aliquat 336 concentration of 99.64 mM and EDTA concentration of 48.86 mM—where 95.89% of Cd(II) was extracted with the least extracted Cu(II) of 0.59%. A second-order model was fitted for optimization of Cd(II) extraction with a R2 value of 0.998, and ANOVA results revealed that the model adequately fitted the data at a 5% significance level. Interaction between Aliquat 336 and Cd(II) has been proven via FTIR qualitative analysis, whereas the addition of TBP does not affect the extraction mechanism.
Highlights
Stringent environmental regulations and depletion of the world’s mineral resources have urged for the removal and recovery of heavy metals from the metallurgical production and hydrometallurgical processing waste and secondary sources in complex leach solutions
The results indicated that the addition of trioctylphosphine oxide (TOPO) into Aliquat 336 did not improve the extraction efficiency as compared with Aliquat 336 as a single extractant whereas, Aliquat 336 with tributyl phosphate (TBP) in toluene intensified the extraction of Cd(II) over Cu(II)
Investigation on the addition of phase modifier at different pH clearly revealed that TBP enhanced the separability of Cd(II) over Cu(II) at pH 4.5 to pH 5.5
Summary
Stringent environmental regulations and depletion of the world’s mineral resources have urged for the removal and recovery of heavy metals from the metallurgical production and hydrometallurgical processing waste and secondary sources in complex leach solutions. Despite their toxicity, Cd and Cu are used in industries, such as metal refining, mining, electroplating, and manufacturing of alloys. Selective separation and recovery of Cd from wastewater containing various metallic constituents can be achieved by chemical precipitation, adsorption, ion exchange, solvent extraction, electrolysis, etc. Different metal species with almost identical valence configurations in the same mixture allows co-transport, and it makes selective extraction a tough challenge. Selective extraction of Cd(II) is feasible in the presence of Zn(II), Ni(II), Co(II), Mn(II), Fe(II), Ca(II), and Mg(II), but Cu(II) and Pb(II) were found to be co-extracted with
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