MECHANISMS INVOLVED IN SOIL CONDITIONING BY POLYMERS

Abstract

Three different soils (two sodic and calcareous and one very acid and serpentine-like) was mixed with polyanion and polycation polymers and with a polysaccharide in suspension and passed the flocculated particles through sieves of different size openings for measurement of components. Including (NH/sub 4/)/sub 2/SO/sub 4/ in the suspension resulted in more complete flocculation with high pH soils and less with the acid soil. In contrast, with the polycation the (NH/sub 4/)/sub 2/SO/sub 4/ resulted in less flocculation for all three soils. Liming the acid soil to pH 7 increased flocculation for both the polyanion and the polycation. The polyanion resulted in more flocculation on calcareous than on acid soil, and the reverse occurred for the polycation. These results indicate that the salt effect was that of bringing clay particles closely enough together so that several of them could be bound with a common polyanion. The binding then would occur many times with polyanions for each aggregate of clay particles. Ion bridging is an important phenomenon in which polyvalent cations may be shared with polymer and clay in the flocculation-aggregation process. The addition of a polysaccharide with the polyanion gives additive to synergistic responses, indicating that there is cross-linking betweenmore » the two polymers. The total effect resembles a brush heap that secures stability for the flocculated particles.« less