2-Ethylhexanal OximeによるNi<sup>2+</sup>の抽出速度におよぼす添加剤の効果

Abstract

In the previous work, it was found that the extraction rate of Ni2+ with 2-ethylhexanal oxime (abbreviated as EHO) from wasted FeCl3 etching solution was extremely slow. This is because the substitution reaction of the hydrated Ni2+ ions, Ni(H2O)62+ with the extractant is a rate determining step.In order to improve the extraction rate of Ni2+, the extraction rate was investigated by adding D2EHPA or TBP as a second extractant to the main extractant EHO. The big enhancement of Ni2+ extraction rate is found when the second extractants, D2EHPA or TBP, are added in a small amount to EHO. As an example, the addition of 0.1mol/dm3 D2EHPA and TBP results in 18 and 30 times enhancement of Ni2+ extraction. The extraction rate equation for Ni2+ is induced so as to be a reversible reaction. Then, the apparent rate constants for forward and backward reactions were calculated according to the induced rate equation. The forward extraction rate is proportional to the 1st order of Ni2+ concentration, TBP concentration and EHO concentration, while the backward extraction rate is proportional to the 1st order of Ni2+ concentration, which is written as,-d[Ni2+] / dt = kf*[Ni2+]aq [EHO]org [TBP]org -kb*[Ni2+]aqThe above extraction rate expression is reasonably explained by imaging the following elementary reactions and assuming the second reaction to be a rate determining step,Ni(H2O)62+ + TBPad ⇔ Ni(H2O)52+ · TBPadNi(H2O)52+ · TBPad + EHOad → Ni(H2O)52+ · EHOad + TBPad