Extraction behaviour of Fe3+ from chloride solution by technical grade D2 EHPA: A comparison with the results obtained by analytical grade

Abstract

The solvent extraction of Fe3- from chloride solution by technical grade (t.g) di-(2-ethylhexyl) phosphoric acid, D2EHPA dissolved in kerosene has been investigated over a wide range of aqueous acidity as a function of phase contact time, concentrations of Fe3+, HCl, H + and Cl- in the aqueous phase, D2EHPA concentration in the organic phase and temperature and the results have been compared to that reported for analytical grade (a.g). Equilibrium time is 60 min, compared to 50 min for a.g. Natures of Fe3+ concentration dependences are not similar and the values of extraction ratio are usually hundred times greater for t.g. than for a.g. under similar conditions. The HCl dependence plots pass through a maximum and a minimum at 1.6 M and 1.1 M HCl, respectively, whereas, these are at 1.2 M and 0.3 M HCl, respectively, for a.g. At [Cl-] = 3 M, the shape of H+ dependence plot for t.g. reagent differs widely from that for the a.g. The extraction is also found to be immenesely dependent on [Cl-] for both the grades of extradant, but the extent of dependence under similar condition depends on the grade of extradant used. The extradant dependences arc lower for t.g. compared to those for a.g. Reactions are exothermic in higher temperature region, whereas, the extraction is almost independent of temperature in its lower regions. The apparent enthalpy change, ΔH value in the higher temperature region is decreased with decreasing H+ concentration in the aqueous phase. But the opposite trend was observed with a.g. The loading capacity depends on the aqueous acidities and grades of D2EHPA. It is 13.05 and 6.83 g of Fe3+ per 100 g D2EHPA(t.g.) at [HCl] of 0.13 and 3 M, respectively, compared to 8.38 and 3.14 g of Fe3- per 100 g D2EHPA (a.g.) at [HCl] of 0.05 and 1 M, respectively. Mechanism of extraction is complicated by the simultaneous extractions of Fe3+, FeCl2+, FeCl+, FeCl 3, HFeCl4, etc. in both cases. It is observed that 99.4 % of iron species extracted by D2EHPA (t.g.) in the organic phase can be stripped by 5 M HCl in three stages at organic to aqueous phase ratio of unity. Organic phase after one cycle can be recycled after adding 0.72 g dm-3 mono-(2-ethylhexyl) phosphoric acid, M2EHPA.

Publication Title

Pakistan Journal of Scientific and Industrial Research

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