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Effect of Na-Hexametaphosphate on the Hydraulic Conductivity of Kaolinite-Sand Mixtures

Published online by Cambridge University Press:  02 April 2024

G. J. Levy ,
I. Shainberg ,
N. Alperovitch  and
A. J. van der Merwe
G. J. Levy
Affiliation:
Institute of Soils and Water, Agricultural Research Organization, P.O. Box 6, Bet Dagan 50250, Israel
I. Shainberg
Affiliation:
Institute of Soils and Water, Agricultural Research Organization, P.O. Box 6, Bet Dagan 50250, Israel
N. Alperovitch
Affiliation:
Institute of Soils and Water, Agricultural Research Organization, P.O. Box 6, Bet Dagan 50250, Israel
A. J. van der Merwe
Affiliation:
Soil and Irrigation Research Institute, Private Bag X79, Pretoria 0001, Republic of South Africa
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Abstract

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Mixtures of kaolinite clay and quartz sand were packed in columns and leached with NaCl-CaCl2 solutions of different concentrations (ranging from 0.5 M to distilled water) having sodium adsorption ratios (SAR) of 5, 10 and 20. Sodium hexametaphosphate (NaHMP) (10 g/m3) was added to each solution. Changes in the hydraulic conductivity (HC) and clay concentration in the effluent were measured, and the dispersion of the clay was evaluated. In the absence of NaHMP, using distilled water instead of 0.01 M solutions caused some reduction in the HC; the reduction became more severe as the SAR increased. At SAR 20 the HC dropped to 73% of that obtained when the 0.5 M salt solution was used. This reduction in HC was related to increases in the pH of the effluent and partial dispersion of the clay. On adding the NaHMP to the leaching solutions, a marked decrease in the HC and severe clay dispersion were observed at all SAR levels, if the kaolinite-sand mixtures were leached with dilute solutions and distilled water. The HC dropped to 40% of that obtained when leaching with 0.5 M salt solution, and dispersed clay in the effluent peaked at about 1% in the SAR 20 treatment following leaching with distilled water. The observed reduction in the HC of the kaolinite-sand mixture when NaHMP was added to the leaching solutions was due to the dispersive effect of NaHMP and sodium on the kaolinite. The polyanion NaHMP reduced the edge-to-face particle interactions, thereby enabling the dimise double-layer repulsion forces to predominate. Following addition of the polyphosphate, the response of kaolinite to sodium and electrolyte concentration was similar to that reported in the literature for smectite.

Keywords

DispersionHexametaphosphateHydraulic conductivityKaoliniteSandSodium adsorption ratio
Type
Research Article
Information
Clays and Clay Minerals , Volume 39 , Issue 2 , April 1991 , pp. 131 - 136
Copyright
Copyright © 1991, The Clay Minerals Society

Footnotes

1

Contribution from the Soil and Irrigation Research Institute, Private Bag X79, Pretoria 0001, Republic of South Africa.

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