Fundamental studies on metal–humic acid interactions

There are three aims of this work. The first is to further knowledge on metal binding to humic acids (HA's), particularly to further understand which functional groups on the HA molecule metals complex to. The second is to find a method which can provide direct evidence of the formation of ternary complexes of humic acid, metal and carbonate. The third is to compare the stability constants of metals to HA(aqueous) and to HA(solid). Investigations are carried out at pH 6 using CPMAS SSNMR spectroscopy. Metal binding to HA is explored using the following metals: Eu, Cd, Ce, Ca, Ba, Sr and Zn. It is shown that a 2 ppm significant chemical shift difference is appropriate for this work, and that only metals binding to the functional groups of interest or close by can cause chemical shift differences above this. [Continues.]