weight (900-21,000 g/mol) acrylic acid (PAA) homopoly-The interactions between acrylic-maleic acid (PAA-PMLA) comer. The major part of the PCA ultimately entering sewage polymer with clay minerals are investigated in terms of adsorption/ water after the washing process is adsorbed by the active desorption behavior. The adsorption isotherms were obtained as sludge in the water treatment plants. However, the use of a function of clay mineral structures, pH and ionic strength by the sludge as a fertilizer introduces the PCA into the soil sensitive polyelectrolyte titration and radiotracer methods. The environment. Though PCAs are reported to be nontoxic to nature and the location of binding sites for PAA-PMLA copolymammals and compatible with the ecosystem (4), their poor mer on aluminol sites at the edge surface can be stated. In the biodegradability will lead to an accumulation over an excase of the adsorption on kaolinite, the pH-dependent interaction tended period of time. Thus, there is a need to evaluate the in relatively low ionic strength is discussed not only in terms of electrostatic contributions, but evidences for a ligand exchange environmental mobility of PCA in soils especially in terms mechanism are also presented. Increasing the ionic strength also of adsorption-desorption processes at clay mineral surfaces enhances the adsorption by a screening of the charges in the adas very reactive inorganic soil components (5). In this consorbed layer especially when the charges of the copolymer and the text, interest is centered on the effects of widely distributed surface are of the same sign. The adsorbed PAA-PMLA copolyphosphate compounds, which are known to strongly adsorb mer can be displaced by phosphate compounds such as monophoson soil metal oxides and clay mineral surfaces at the same phate and sodium tripolyphosphate (STP). The observed desorpbinding sites as those of natural organic acids (6, 7). Indeed, tion process results from a competition between PAA-PMLA cothough sodium tripolyphosphate (STP) is disappearing from polymer and phosphate compounds for the same binding sites on detergent formulations, its presence in soil, as well as other the kaolinite surface. Adsorption equilibrium constants can thus phosphate compounds from fertilizer sources, is also exbe derived from single and mixture adsorption isotherms. Effects pected to influence the interactions of PCA with clay minerdue to the heterogeneity of the kaolinite surface and to the conformation of the adsorbed PAA-PMLA copolymer are also discussed. als. The adsorption of polyelectrolytes at clay mineral sur-Strongly bound PAA-PMLA copolymer traces support the ligand faces has been reviewed (8). Because of industrial and agroexchange mechanism at the aluminol sites of the edge surface. nomical interests, most investigations about the adsorption Clay minerals may thus act as natural barriers in the soil transport of anionic polyelectrolytes on clay minerals have focused of the polycarboxylates used in phosphate-free detergents. ᭧ 1997 their attention on the influence of the polymer on the disper-Academic Press sion state (9-11). The charge duality on a clay surface (12) Key Words: polycarboxylic acid; clay minerals; phosphate; adsorprenders the question about the location of the adsorption tion; desorption; kaolinite.
sites more difficult. Equilibrium adsorption measurements (12-14), rheological studies (15-18), electrokinetic investigations (18,19), sediment volume and turbidity results (17,