Pedosphere 9(3): 227--232, 1999
ISSN 1002-0160/CN 32-1315/P
©1999 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Sulfate-exchange alkalinity of ferralsol colloid
ZHANG Gang-Ya and ZHANG Xiao-Nian
Institute of Soil Science, the Chinese Academy of Sciences, Nanjing 210008 (China)
ABSTRACT
      The amount of OH- replaced by sulfate, i.e., sulfate-exchange alkalinity, from the electric double layer of ferralsol colloid was measured quantitatively in different conditions with an automatic titration equipment. The amount of OH- release increased with the amount of Na2SO4 added and decreased with raising pH in the suspension of ferralsol colloid. The exchange acidity was displayed as pH was higher than 5.6. If the negative effect of sodium ions was offset, the amount of OH- replaced by sulfate was larger than the original amount of OH- released in the pH range of lower than 5.8. The amount of OH- released decreased rapidly as pH was higher than 6.0 and dropped to zero when pH reached 6.5. In the solution of 2.0 mol L-1 NaClO4, the amount of OH- replaced by sulfate from the surface of ferralsol colloid could be considered as the amount of OH- adsorbed by ligand exchange reaction. The amount of OH- released in the solution of NaClO4 concentration below 2.0 mol L-1 from which the amount of OH- adsorbed by ligand exchange reaction was subtracted could be considered as the OH- adsorbed by electrostatic force. The OH- adsorbed by electrostatic force decreased with increases in the concentration of NaClO4 and pH and increased almost linearly with the increasing amount of Na2SO4 added. The percentages of OH- adsorbed by electrostatic force in water and in the electrolyte solutions of 0.05 and 0.5 mol L-1 NaClO4 in the total OH- released were calculated, respectively.
Key Words:  ferralsol colloid, OH- release, sulfate-exchange alkalinity
Citation: Zhang, G. Y. and Zhang, X. N. 1999. Sulfate-exchange alkalinity of ferralsol colloid. Pedosphere. 9(3): 227-232.
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