TY - JOUR
T1 - Surface charge characteristics of kaolinitic tropical soils
AU - Chorover, Jon
AU - Sposito, Garrison
N1 - Funding Information:
Acknowledgments-Gratitude is expressed to Cheryl Palm, Peter Mo-tavalli, and Paul Smithson for their gracious provision of the soil samples and basic physicochemical data on those samples in support of the present study, and to Laurent Charlet, Charalambos Papelis, and Paul Wersin for their most helpful reviews. Thanks also to Terri DeLuca for excellent typing of the manuscript. The research reported in this paper was supported in part by NSF grant no. EAR 92-21258 and by the Keamey Foundation of Soil Science.
PY - 1995/3
Y1 - 1995/3
N2 - Surface charge properties of four representative kaolinitic soils from the humid tropics (Brazil) were investigated by a methodology involving independent measurements of net total permanent and variable charge components. Permanent structural charge was determined by Cs+ adsorption, whereas variable charge was quantified by simultaneous proton titration and background electrolyte (LiCl) adsorption measurements. Data were obtained for homoionic soils suspended in LiCl solutions of ionic strength 1-10 mmol L-1 and pH value 2-6. Corrections were made in the titration data for proton consumption resulting from dissolution and aqueous-phase complexation reactions. Conjunctive use of proton titration and electrolyte adsorption data yielded independent assessments of proton surface charge densities and points of zero charge. The surface charge data were tested successfully for consistency with the law of surface charge balance. Three of the soils exhibited similar surface charge behavior, with no pronounced effect of differences in either organic C or Fe and aluminum oxide content. One soil containing significant manganese oxides showed points of zero charge well below those of the other three soils. The point of zero net charge (p.z.n.c) for the soils was ≤4, lower than values reported for specimen kaolinite. The point of zero net proton charge (p.z.n.p.c.) increased with decreasing ionic strength. In all cases, the presence of small quantities of structural charge in 2:1 clay minerals had a significant effect on surface charge properties; e.g., for all soils, p.z.n.c. < p.z.n.p.c. These characteristics of surface charge were shown to be consistent with the behavior of a mixture of kaolinite, organic matter, and a small quantity of 2:1 clay minerals. In conformity with the law of surface charge balance, ionic strength effects were found to be removed by plotting net adsorbed ion charge against net proton surface charge density.
AB - Surface charge properties of four representative kaolinitic soils from the humid tropics (Brazil) were investigated by a methodology involving independent measurements of net total permanent and variable charge components. Permanent structural charge was determined by Cs+ adsorption, whereas variable charge was quantified by simultaneous proton titration and background electrolyte (LiCl) adsorption measurements. Data were obtained for homoionic soils suspended in LiCl solutions of ionic strength 1-10 mmol L-1 and pH value 2-6. Corrections were made in the titration data for proton consumption resulting from dissolution and aqueous-phase complexation reactions. Conjunctive use of proton titration and electrolyte adsorption data yielded independent assessments of proton surface charge densities and points of zero charge. The surface charge data were tested successfully for consistency with the law of surface charge balance. Three of the soils exhibited similar surface charge behavior, with no pronounced effect of differences in either organic C or Fe and aluminum oxide content. One soil containing significant manganese oxides showed points of zero charge well below those of the other three soils. The point of zero net charge (p.z.n.c) for the soils was ≤4, lower than values reported for specimen kaolinite. The point of zero net proton charge (p.z.n.p.c.) increased with decreasing ionic strength. In all cases, the presence of small quantities of structural charge in 2:1 clay minerals had a significant effect on surface charge properties; e.g., for all soils, p.z.n.c. < p.z.n.p.c. These characteristics of surface charge were shown to be consistent with the behavior of a mixture of kaolinite, organic matter, and a small quantity of 2:1 clay minerals. In conformity with the law of surface charge balance, ionic strength effects were found to be removed by plotting net adsorbed ion charge against net proton surface charge density.
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U2 - 10.1016/0016-7037(94)00357-2
DO - 10.1016/0016-7037(94)00357-2
M3 - Article
AN - SCOPUS:10444251454
SN - 0016-7037
VL - 59
SP - 875
EP - 884
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 5
ER -