KINETIC-STUDY OF THE SPECIATION OF COPPER(II) BOUND TO HUMIC-ACID

The kinetically distinguishable species present in a solution of Cu(II ) equilibrated with a soil humic acid have been identified by a kineti c method based on ligand displacement reactions with 3-propyl-5-hydrox y-5-(d-arabino-tetrahydroxybutyl) thiozolidine-2-thione (PHTTT). An ap proximate Laplace transform is used to assign the minimum number of co mponents and approximate their associated concentrations and dissociat ion rate constants. The initial parameters are refined by a non-linear multi-exponential least squares regression routine. The two rate cons tants 0.093 and 0.0077 sec(-1) consistently represent the middle and s low components of the copper-humic acid complex (CuHA). A fast compone nt which reacts on mixing is the major component present; Species conc entrations vary in a reasonable way with pH and HA/Cu(II) ratio suppor ting the conclusion that the speciation model has chemical significanc e.