Selective separation of Co(II) from aqueous acidic solutions containing thiocyanate ions has been achieved by using 2-benzylpyridine (BPy) dissolved in benzene. Optimum conditions of extraction by 0.1M BPy are: 0.05M (HCl, HNO3) or 0.01M H2SO4+1 M KSCN. Ascorbate and sulfate ions do not affect the extraction of cobalt(II), whereas acetate, citrate and oxalate ions lower the extraction. Separation of cobalt(II) from Mn, Cr, Hf, Fe, Y, Ce, Cd, Sr, Cs and several rare earth elements can be achieved in a single extraction. Slope analysis by log-log plot reveals that neutral cobalt-thiocyanate species is extracted with the probable formula of the extracted complex as Co(BPY)3 (SCN)2.
Liquid — liquid extraction of Ag(I) by diphenyl-2-pyridylmethane (DPPM) in benzene from aqueous nitric and sulfuric acid solutions containing thiocyanate ions has been studied at ambient temperature (24±2 °C). The metal is extracted quantitatively from 0.01M HNO3+0.02M KSCN; or 0.25M H2SO4+0.02M KSCN by 0.1M DPPM (optimum extraction conditions). Slope analysis indicates that two types of ion-pair complexes i.e. [(DPPMH)+·Ag(SCN)
] and [(DPPMH)
] are involved in the extraction process. Separation factors determined at optimum conditions reveal the separation of Ag(I) from Cs(I), Br(I), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Fe(III), Au(III) (from HNO3 solution only), Cr(III), Hf(IV), Ta(V), Sn(IV) and Cr(VI). With the exception of thiosulfate, other complexing anions like ascorbate, acetate, citrate, oxalate do not hinder the extraction of Ag(I) under optimum conditions.
The batch kinetics of Fe(III) adsorption on HTTA-loaded polyurethane (PU) foam have been investigated. The rate of controlling the adsorption is found to be intraparticle diffusion. The reaction rate of adsorption and desorption was also evaluated and found to increase and decrease with temperature, respectively. This indicates an endothermic adsorption behavior of Fe(III) on HTTA loaded PU foam. The activation energy of adsorption (80±10 kJ·mol–1) and of desorption (–45±±2 kJ· mol–1) indicates the chemical adsorption rather than physical adsorption. The isosteric heat of adsorption (
Hads) was found to be –82.7±5.05 kJ·mol–1. This shows the formation of new chemical bonds among Fe(III)-HTTA-PU foam. The thermodynamic parameters of
S, and equilibrium constantKc have been calculated. These functions further support that the process of adsorption of Fe(III) on HTTA-loaded PU foam is endothermic and chemisorption, stabilized through thermodynamic functions.
The sorption of Fe(III) at low pH range from 1 to 4.5 on open cell polyether type HTTA-loaded polyurethane foam has been carried out using batch technique. The optimum shaking time for 2.5· 10–4M solution of Fe(III) was found to be 30 minutes. The concept of macropore and micropore nature of polyurethane foam sorbent offers unique advantages of adsorption. Freundlich and Langmuir adsorption isotherms are followed at low concentration range from 1·10–4 to 3·10–4M solution of Fe(III). The Freundlich constant (1/n=0.46±0.013 andK=9.16±1.39 mg·g–1) and Langmuir isotherm constants(M=21.78 mg·g–1 andb=88.41±9.731·g–1) were established. The sorption mean free energyE=12.22±0.09 kJ·mol–1 and loading capacityCm=145.21±6.1 mg·g–1 were evaluated using Dubinin-Radushkevich isotherm, which suggested that the adsorption mechanism was chemisorption.