THE ROLE OF SURFACE CONFORMATIONS IN THE DEPOSITION KINETICS OF HUMICMATTER-COATED COLLOIDS IN POROUS-MEDIA

The effects of humic matter surface conformations on the deposition ra tes of polystyrene latex colloids in packed beds of quartz sand were i nvestigated. Positively- and negatively-charged latex spheres were coa ted with two well-characterized humic substances and their attachment efficiencies to quartz collectors were determined for varying concentr ations of NaCl between 0.02 and 0.8 M, at pH 7.4. The deposition behav ior of colloids was highly dependent upon the surface conformations of the adsorbed humic matter. Latex colloids coated with the larger mole cular size peat humic acid possessed smaller attachment efficiencies t han the same colloids in the presence of a smaller molecular size but more acidic surface water fulvic acid. The negatively-charged sulfate latex particles were more stable than the positively-charged amidine l atex particles when coated with the same humic matter at most solution conditions used here. The stability of peat humic acid-coated particl es was highly susceptible to changes in salt concentrations up to abou t [NaCl] = 0.6 M, which may be attributed to the presence of electrost eric interactions, and/or the reduction in the solvency and the result ing collapse of the adsorbed layer of the humic matter. Our results su ggest that the differences in the steric interaction forces brought ab out by the surface conformations are primarily responsible for the obs erved differences in the deposition behavior of the coated colloids fo r the ionic strength conditions used here.