Extraction of zinc(II), iron(II) and iron(III) from chloride media with dibutylbutylphosphonate

The extraction of zinc(II), iron(II) and iron(III) with solutions of dibutylbutylphosphonate (DBBP) from hydrochloric acid solutions was studied. Iron(II) was only slightly extracted by DBBP. The isotherms of zinc(II) extraction with DBBP were compared with those for tributylphosphate (TBP). They indicated that extraction efficiency was higher for DBBP than for TBP. The transfer of iron(III) was effective, due to the presence of a neutral chlorocomplex at high Cl− and HCl concentrations. Thus, selective zinc(II) separation from strong chloride solution containing iron(III) with DBBP was not possible. Addition of kerosene (20–40 vol.%) increased the hydrophobicity of DBBP while slightly decreasing the efficiency of zinc(II) extraction. As a result, water content in the organic phase decreased with decreasing DBBP concentration from almost 9 to about 4%. Hydrochloric acid co-extraction was observed, and it decreased in the following order of the accompanying metal ions: Zn(II) > Fe(II) > Fe(III) for 100 and 80% DBBP. Above a DBBP concentration of 40 vol.% zinc(II) complexes with two DBBP molecules in the organic phase. At lower DBBP concentrations zinc(II) species form a complex with only one DBBP molecule. DBBP enables selective removal of zinc(II) in the presence of iron(II). The selectivity of zinc(II) extraction over iron(II) with 80% DBBP is very high and exceeds 103. Zinc(II) can be effectively stripped (over 90%) from loaded DBBP with water in three stages.