The extraction of niobium (V), tantalum (V), mercury (II), silver (I), cobalt (II), iron (III) and cadmium (II) by di(n-octyl) arsinic acid (HDOAA) in chloroform
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1975
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Abstract
The extraction of Nb(V) and Ta(V) from HCl, H₂SO₄ and H₂C₂O₄ solutions, Hg(II) from HCl solutions, Ag(I) from HNO₃ solutions, Co (II) from HCl solutions, Fe(III) from HCl, HNO₃, H₂SO₄, and HCIO₄ solutions and Cd(II) from HCl solutions by 0.1 M solutions of dioctylarsinic acid, (n-C₈H�₇)₂AsOOH (HDOAA) in chloroform was investigated. The extraction of these metal ions was studied as a function of the equilibrium aqueous phase pH and the reagent concentration using radionuclides as tracers. In the niobium and tantalum extraction experiments the oxalates MO(OH)C₂O₄(M=Nb,Ta) were employed. Both of the elements were efficiently extracted from strongly acidic aqueous solutions with maximum E°[subscript a] values of 93 (from 6 M HCl) and 125 (from 1 M H₂SO₄) for the niobium system and 250 (from 6 M HCl) and 386 (from 4 M H₂SO₄) for the tantalum system. The pH and reagent dependence studies suggested that a monobasic trinuclear niobium species is extracted as an ion pair with 10 HDOAA molecules associated with the trimer. Tentatively, the formula (H₂DOAA)�[Nb₃-(HDOAA)g (C₂O₄,OH,O,H₂O)[subscript n]]� is proposed. The composition of the extracted tantalum complex was found to be dependent on the shaking time. After shaking for one hour the data suggested the formula (H₂DOAA)�[Ta(HDOAA)₂(C₂O₄,O,OH)[subscript n]]� for the extracted species whereas after 36 hours shaking the tantalum to HDOAA ratio decreased from 2:1 to 1:1. ...
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Chemistry