Aggregation and charging of natural allophane particles in the presence of oxyanions

Abstract

Allophane is a typical clay mineral in young volcanic ash soil with special and complex structures and properties. The aggregation-dispersion and charging behaviors of natural allophane may have implications on sustainable agriculture and environment. Oxyanions, such as phosphate and arsenate, may also be related to many environmental resource problems. To investigate the aggregation and charging behaviors of allophane in the presence of oxyanions, the stability ratio (W) and electrophoretic mobility (EPM) of allophane were measured. The results of EPM, W and the values of CCCs show ion specific effect, which is not explicitly considered by the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory. However, the relationship between critical coagulation ionic strength (CCIS) and surface charge density from EPM based on DLVO theory with the Debye-Huckel (DH) approximation is in good agreement with the experimental CCIS. This agreement indicates that the DLVO forces controlled by ionic strength and electrokinetic charge are the driving forces in the aggregation process of natural allophane particles in the presence of oxyanions.