Galvanic stripping of Fe⁺³ and Pb⁺² ions and dissolution of metallic Fe, Zn, Pb and Cd using Di(2-ethylhexyl)phosphoric acid
"Two systems were evaluated using the principles of the galvanic stripping process. One of them, the removal of Pb+2 ions from di-2(ethylhexyl) phosphoric acid (D2EHPA) was performed using metallic zinc. The other, the removal of Fe+3 ions from D2EHPA used metallic iron as reductant and was performed simultaneously with the organic phase using a slightly acidic aqueous solution of hydrochloric acid. In addition, the dissolution of metallic zinc, iron, lead, and cadmium in D2EHPA was studied in order to better understand the anodic step in the mechanism of the galvanic stripping process. Increased temperature was found to dramatically improve the galvanic stripping of Pb+2 and Fe+3 ions, while agitation was found to have a negligible effect. The calculated activation energies indicate that it is a chemically-controlled process. Conversely, agitation strongly influenced the dissolution of Zn, Fe and Pb metals while temperature was less of a factor, suggesting that dissolution is governed by a diffusion-controlled process. An optimum amount of oxygen was necessary to initiate the dissolution of the metals. No dissolution was accomplished when oxygen was removed by nitrogen sparging or when oxygen was present in excess. Also the dissolution of metals occurred only when a certain amount of water was present in the organic and the other variables became significant only if this moisture condition was satisfied. However, each metal had a different response to the critical amount of water required to maximize the reaction"--Abstract, page iv.
Missouri University of Science and Technology
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