Surface charge characteristics of soil colloids of some different soil types

Abstract

AbstractMost of the soil samples, on the basis of Δ pH measurements, were observed to carry net negative surface charges, except six samples, which carried net positive surface charges. In one case, the net surface charge was noticed to be zero.According to surface charge‐pH curves, the colloid surfaces of soil samples of a Hapludalf and a Luvisol, were characterized as constant charge type. Their zero point of charge (zpc) was very low (near pH 3.0), and remained identical throughout the depth. The colloid surfaces of Tropudalf samples, especially those of B and C horizons, and net positively charged samples were characterized as constant potential type. In the former, the zpc increased from pH 3.45 (A horizon‐D3) to 6.35 (C horizon‐D1). Of all the samples studied, the highest zpc (pH 6.75) was recorded in one of the net positively charged samples (L24). The electrochemical behaviour of constant potential type colloids was therefore similar to that exhibited by many metallic oxides.ΔG° values in Hapludalf and Luvisol colloids were near to H bonding (‐5 to‐10 kcal mol−1), whereas in others the values were higher than that for H bonding, except for A horizons of Tropudalfs.