Author
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Laird, David |
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Submitted to: Soil Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/9/1997 Publication Date: N/A Citation: N/A Interpretive Summary: PAM is a synthetic organic polymer that is widely added to irrigation water to help prevent erosion. PAM is also highly effective for settling suspended sediment in water and for stabilizing existing soil structure. PAM works by binding tightly to soil mineral particles, but no one knows how. We determined that many different chemical and physical processes help PAM bind to mineral particles. The type of soil mineral present determines which processes are involved. In one of those processes, calcium acts like a bridge between clay particles and PAM. In other processes, the PAM binds directly to surfaces of clay mineral particles. Knowledge generated in this study will help scientists and engineers design better agricultural management systems benefitting farmers and the general public by decreasing soil erosion and reducing sediment in rivers and lakes. Technical Abstract: The objectives of this research were to determine the effects of clay mineralogy on the efficacy of cationic and anionic polyacrylamides (PAM) as flocculents for dispersed clays and to evaluate bonding mechanisms between clay mineral surfaces and both cationic and anionic PAM. A relative flocculation index was used to quantify the intersection between PAM and the Ca- and Na- forms of kaolinite, illite, and quartz. The cationic PAM was highly effective for flocculating all three minerals regardless of the electrolyte concentration or saturating cation. Under basic (pH=10.9) conditions, the cationic PAM was slightly less effective than under neutral (pH=5.9-8.2) or acidic (pH=3.4) conditions. Positive charge functional groups on the cationic PAM are believed to bond directly with negative charge sites on the mineral surfaces. The efficacy of anionic PAM as a flocculent varied with saturating cation (Ca>>Na), mineralogy (kaolinite>illite>>quartz), and treatment (acid>salt>H2O>base). The results suggest that cation bridging (PAM-Ca-clay) is the major bonding mechanisms between anionic PAM and clay mineral surfaces. However, hydrogen bonding between electronegative moieties on the PAM and protonated nonbridging aluminol groups on lateral edges of kaolinite and illite and hydrophobic bonding between carbon chain of the anionic PAM and basal surfaces of kaolinite also were suggested by the flocculation data. |
