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This article in SSSAJ

  1. Vol. 57 No. 5, p. 1222-1228
     
    Received: May 1, 1992
    Published: Sept, 1993


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doi:10.2136/sssaj1993.03615995005700050011x

Soil Surface Charge Evaluation by Back-titration: I. Theory and Method Development

  1. Martin Duquette and
  2. William Hendershot 
  1. SNC-Lavalin Environment Inc., 2, Place Felix-Martin, Montreal, QC, H2Z 1Z3, Canada
    Dep. of Renewable Resources, McGill Univ., Macdonald Campus, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada

Abstract

Abstract

Until recently, surface charge chemistry of soils has been measured using two different approaches: ion adsorption and potentiometric titration. The former provides a good measure of both anion-exchange capacity (AEC) and cation-exchange capacity (CEC) as a function of pH, although the procedure is time consuming. Potentiometric titration is more rapid, but the resulting curve overestimates the change in surface charge with pH. The error is largely due to consumption of H+ and OH by dissolution and hydrolysis reactions with dissolved ions instead of being limited to protonation-deprotonation reactions of surface charge sites. Our objective was to develop the theoretical aspects of the determination of surface charge using a back-titration method. After suspension in Ca(NO3)2, a subsample of the soil is titrated slowly to pH 3, and then back-titrated to pH 8 or 10. A second subsample is similarly titrated to pH 3; the soil and the supernatant solution are separated by centrifugation and filtering; only the supernatant solution is back-titrated. The difference between the two titration curves represents the consumption of OH by surface reactions corrected for dissolution and other solution reactions. The proposed method provides a relatively rapid means of obtaining pH-dependent surface charge using potentiometric titration while giving results comparable to those obtained by ion adsorption.

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