INTERACTION BETWEEN CA2-CARBON - IMPLICATIONS FOR METAL MOBILIZATION(AND DISSOLVED ORGANIC)

To investigate the role of dissolved Ca on the sorption and complexati on behaviour of dissolved organic carbon (DOC), and the effect on diss olved Cu concentration, batch sorption studies and titration experimen ts have been performed. Both adsorption and desorption studies showed that the DOC concentration depends on the presence of Ca. With increas ing Ca content, the DOC concentration decreased as a result of sorptio n and precipitation processes. The formation of aqueous Ca-DOC complex es could be described well with a 1:1 Ca:DOC ratio. Log K-CaDOC values for the formation of Ca-DOC complexes ranged from 3.7 to 4 in the low pH range (3.5 to 6, interaction with carboxyl groups) and from 5.8 to 6 in the pH range from 7 to 9 (interaction with phenolic groups). The results indicate that a large part of the available DOC is in a Ca fo rm at near neutral pH values. In batch sorption experiments, the addit ion of Ca2+ significantly reduced the DOC as well as the Cu concentrat ion in solution. This indicates that sorption of Ca-DOC complexes at n ear neutral pH is more important in regulating the Cu solution concent ration compared to cation exchange processes. (C) 1996 Elsevier Scienc e Ltd