Adsorption Isotherms of Polyanions on Soils Using Tritium Labeled Compounds
- Arie Nadler and
- J. Letey
Although the effects of polymers on various soil physical properties have been investigated, adsorption of polymers by soils has not been extensively studied. Adsorption isotherms were determined by the batch technique for three tritium-labeled polyanions on one soil which received various pretreatments. Two polyacrylamide (PAM) compounds in which the NH2 was substituted with OH at 2% (2J) and 21% (21J), rendering them negatively charged, were used. Additionally, a guar compound (4246) used in the study was negatively charged and had a lower molecular weight than PAM. The soil was used without pretreatment and also with pretreatment to create a Ca soil, Na soil, organic matter-depleted soil, and high-pH soil. Polyanion type had a relatively greater effect than did soil pretreatment on adsorption, except for the Na soil, which had very low adsorption as compared to the other soil pretreatments. The more negatively charged polyanions (21J and 4246) had linear adsorption isotherms except for 21J on the Na soil. The 2J had adsorption isotherms that plateaued at higher concentrations. The amount of adsorption was in the general order 21J > 4246 > 2J. The exception was for the Na soil in which adsorption for all polymers was low and in the order 4246 > 2J > 21J. Aggregate stability was determined by wet sieving on all the samples. No direct association between the amount of adsorption and aggregate stability was found. The general effectiveness of the polyanions for improving aggregate stability of the natural soil was in the order 2J > 21J > 4246. The reverse trend was observed for the Na soil.
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