二价金属离子萃取速率常数与软硬酸碱规则

The Correlation Between the Extraction Rate Constants of Divalent Metal Ions by HEHEHP and the HSAB Rule

用上升液滴法测定了2-乙基己基膦酸单(2-乙基己基)酯-正辛烷从硝酸介质中萃取镁、钙、锌、镍、铜和铅等二价金属离子的正向初始速率,建立了速率方程,计算出正向萃取反应的速率常数、活化能及活化熵,首次将软硬酸碱规则与金属溶剂萃取速率常数关联.结果表明,在萃取机理相同时,萃取速率常数的大小与金属离子的软硬酸碱标度一致,即萃取过程中,作为酸的被萃取金属离子,其硬度越大,萃取速率常数亦越大,萃取反应的活化能越小.

The kinetics and mechanism of extraction of Mg( Ⅱ ), Ca( Ⅱ ), Zn( Ⅱ ), Ni( Ⅱ ), Cu ( Ⅱ ) and Pb( Ⅱ ) from nitrate medium with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEHEHP) in octane by means of the single drop method were studied at 298 K. The reaction rate constants (kf), the activation energies (Ea) and the activation entropies (ΔS≠) were calculated. The experimental results indicate that the extraction process may be controlled by the following interfacial reactions: M2+ +HA(i) = MA(i)+H+(fast)MA(i)+ 2H2A2(O)= MA2 · 2HA,(O)+HA(i)+H+(slow) and their kf and Ea vary regularly with the change of hardness of Lewis acid.