KINETICS AND MECHANISM OF FORWARD EXTRACTION OF MN(II) FROM SULFATE-ACETATO MEDIUM BY CYANEX 272 DISSOLVED IN KEROSENE USING THE SINGLE-DROP TECHNIQUE

The flux of Mn(II) transfer in -Cyanex 272-kerosene system was investigated using the single-drop technique and the flux method of data treatment. The empirical flux equation at 303K is: F ( f )=10(-3.6) [Mn(II)] (1+10(4.5) [H+])(-1) (1+1.58 [ ])(-1). The activation energy (E ( a )) varies within 15-59kJ/mol depending on experimental conditions. On analyzing the flux equation and with the help of E ( a ) values, it is concluded that either the extraction reaction step Mn2++A(-)-> MnA(+) or the diffusion of reactants (or products) to (or from) the reaction site is rate controlling depending on the reaction parameters. At high pH and at intermediate pH-higher temperature regions, low E ( a ) (<= 20kJ/mol) suggests that the process is under diffusion control. But at low pH and at intermediate pH-lower temperature regions, high E ( a ) (>= 50kJ/mol) suggests that the process is under chemical control. High negative Delta S (+/-) value indicates that the slow extraction reaction step occurs by means of an S(N)2 mechanism.