Removal of Bi, Cd, Co, Cu, Fe, Ni, Pb, and Zn from an aqueous nitrate medium with bis(2-ethylhexyl)phosphoric acid impregnated kapok fiber

Bis(2-ethylhexyl)phosphoric acid (D2EHPA) impregnated fiber (SIF) using a commercial oil sorbent made of kapok fiber as the support has been prepared by a wet method, and its ability to remove metal ions of Bi(III), Cd(II), Co(II), Cu(II), Fe(III), Ni(II),Pb(II), and Zn(II) from single-metal nitrate solutions has been evaluated in comparison with D2EHPA-impregnated resin using XAD7HP as the support (SIR) and solvent extraction with D2EHPA dissolved in a nonpolar organic solvent (SX), where the amount of D2EHPA in each system was the same. The results are summarized as follows: W the removal of each metal by SIF proceeds via cation exchange as in the cases of SIR and SX; (ii) the pH value at 50% metal removal, pH(50), by SIF increases in the order Fe(III) < Bi(III) < Zn(II) < Pb(II) < Cd(II) < Cu(II) < Co(II) < Ni(II), and this order agrees with those by SIR and SX; (iii) the pH50 value for each metal increases in the order SIF < SIR much less than SX; (iv) the loading capacity of Zn(II) by SIF is 1.5 times higher than that by SIR; (v) SIF can be used many times after regeneration by acid treatment as in the case of SIR. The removal rates for Cd(II), Cu(II), Pb(II), and Zn(II) decrease in the order SX > SIF > SIR. In conclusion, SIF is more advantageous than SIR and SX in terms of the amount of D2EHPA necessary for achieving a certain removal percentage and than SIR in terms of the removal rate; thus, the application of SIF to metal-bearing wastewater treatment is highly expected.