Effect of acid on the hydrophysical properties of red clay

Abstract

With the exception of the engineering properties of kaolinite, bentonite, silt and sand, little attention has been paid to how the hydrophysical properties of red clay vary with pH value, even though acid contamination of red clay occurs widely. The purpose of this paper is to investigate the laws and mechanisms for the hydrophysical properties of red clay treated with dilute hydrochloric acid. Tests were performed on a natural red clay from South China to determine how hydrochloric acid influences the hydraulic conductivity, expansibility and shrinkage. The test data are of the mineral composition, main metal oxide and zeta potential of the red clay before and after being soaked in various acidic solutions having pH of 3, 4, 5, 6.5. The results show that the consistency decreased with pH value for decreasing zeta potential. In addition, the hydraulic conductivity first decreased and then increased, but the expansibility and contractility went the other way, as the pH value of solution decreases. These phenomena depend on the decrease of zeta potential, the water intensity entering the montmorillonite crystals cells, and the formation of open void.