חיפוש מתקדם
Soil Technology

M. Malik and J. Letey - Dept. of Soil and Environmental Sciences University of California Riverside, CA 92521, USA

Knowledge of polymer mobility in soil is useful in predicting effective depth of treatment. In this study, solutions containing six tritium labeled polymers were flowed through columns of Arlington soil or acid washed quartz sand. The polymers were three polyacrylamide (PAM) compounds with negative charge density of 40J > 21J > 2J, and three polysaccharide compounds (guar) which had higher positive charge (T-4141), a lower positive charge (CP-14) and negative charge (T-4246).

Breakthrough curves were determined in each case. The ratio of leachate concentration (C) to the of original polymer concentration at the top (C0 did not reach 1 even after more than 20 pore volumes (PV) were allowed to flow through. Less than 5 PV were expected to produce C/C0 equal to 1 from the calculated retardation factor. The concentration in the effluent dropped to undetectable level within about 1 PV after the solution at the top was replaced with untreated water which indicated irreversable polymer adsorption.

Three hypotheses were proposed to explain why C/C0 did not reach 1:

1. Slow penetration of polymers into soil aggregates,

2. multi-layer adsorption, and

3. polymers consist of two or more molecular groups with varying adsorptive capacities.

Experiments were designed to support or reject each hypothesis. The first hypothesis was conclusively rejected. Although the second hypothesis could not be completely rejected, the third hypothesis provided the major effects. A fraction of the polymers are highly mobile whereas a fraction had very low mobility. The mobile fraction could be carried about as deep as water flow, whereas the highly absorbed fraction would be retained very near the soil surface. The effective depth of treatment from a soil physical condition point of view depends on the unknown effectiveness of the mobile polymer fraction in altered soil physical conditions.

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Mobility of polyacrylamide and polysaccharide polymer through soil materials
4

M. Malik and J. Letey - Dept. of Soil and Environmental Sciences University of California Riverside, CA 92521, USA

Mobility of polyacrylamide and polysaccharide polymer through soil materials

Knowledge of polymer mobility in soil is useful in predicting effective depth of treatment. In this study, solutions containing six tritium labeled polymers were flowed through columns of Arlington soil or acid washed quartz sand. The polymers were three polyacrylamide (PAM) compounds with negative charge density of 40J > 21J > 2J, and three polysaccharide compounds (guar) which had higher positive charge (T-4141), a lower positive charge (CP-14) and negative charge (T-4246).

Breakthrough curves were determined in each case. The ratio of leachate concentration (C) to the of original polymer concentration at the top (C0 did not reach 1 even after more than 20 pore volumes (PV) were allowed to flow through. Less than 5 PV were expected to produce C/C0 equal to 1 from the calculated retardation factor. The concentration in the effluent dropped to undetectable level within about 1 PV after the solution at the top was replaced with untreated water which indicated irreversable polymer adsorption.

Three hypotheses were proposed to explain why C/C0 did not reach 1:

1. Slow penetration of polymers into soil aggregates,

2. multi-layer adsorption, and

3. polymers consist of two or more molecular groups with varying adsorptive capacities.

Experiments were designed to support or reject each hypothesis. The first hypothesis was conclusively rejected. Although the second hypothesis could not be completely rejected, the third hypothesis provided the major effects. A fraction of the polymers are highly mobile whereas a fraction had very low mobility. The mobile fraction could be carried about as deep as water flow, whereas the highly absorbed fraction would be retained very near the soil surface. The effective depth of treatment from a soil physical condition point of view depends on the unknown effectiveness of the mobile polymer fraction in altered soil physical conditions.

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