The extraction features of maleic acid by trioctylamine (TOA) were investigated further to study the extraction mechanism.Based on the first part (Ⅰ) of this paper

we proposed an assumption of four kinds of dissolution existing during extraction of maleic acid with TOA

i.e.physical dissolution of maleic in diluent

hydrogen bond action of TOA on maleic acid

ion pair association of maleic acid with TOA

and physical dissolution of maleic acid in complex.A model containing these four kinds of dissolution was set up using Mass Action Law.The results showed that the calculated concentration of maleic acid in organic phase approached the experimental data.The overall distribution coefficient of physical dissolution of solvent was not always equal to the sum of the diluent and complex

where the experimental distribution coefficient was larger than the sum value for MIBK system

smaller than the sum value for chloroform system and equivalent to the sum value for n -octanol system.