Flocculation and Stabilization of Allophane in the Presence of an Anionic Microbial Polysaccharide (Gum Xanthan) and Several of Its Hydrolytic Intermediates

The polymeric effect of gum xanthan (GX) on the stability of allophane at pH 4.5 and 6.5 was compared with the effect of several of its hydrolytic intermediates (hGX). The polymeric effect of GX was manifested by (i) the effective flocculation at low GX concentrations, (ii) the higher stabilizing ability above the flocculation concentration (FC), and (iii) the appreciable ability of deflocculation of (a) flocculated allophane and (b) allophane-halloysite floc, at extremely low concentrations of GX solution at pH 6.5. In contrast to GX, in the presence of sodium polyacrylate, there was a complete lack of deflocculation of the flocculated allophane at pH 6.5. This fact suggests that effective deflocculation is due to the double-stranded wormlike structure of the GX chain with a small but finite flexibility. The fact that flocculated allophane by GX at pH 4.5 still exhibited a positive electrophoretic mobility can be ascribed to the flocculation of allophane particles by bridging with this biopolymer. The relationship between FC of GX and the allophane content in soil clays was also examined.