Influence of surfactant on clay swelling inhibition of weathered crust elution-deposited rare earth ores

Abstract

Clay minerals are the main components of the weathered crust elution-deposited rare earth ores (WREOs), and their swelling properties have a significant effect on the safe and green in-situ leaching of WREOs. Few researches have been reported on the inhibition of clay swelling in WREOs and our teammates used combination of ammonium salts to suppress the clay swelling in previous work. Surfactants combined with (NH4)2SO4 were utilized as inhibitor in this study to reduce the amount of ammonium salts and thus decrease the ammonium pollution. Effects of different surfactants on inhibition of clay swelling were investigated, and the swelling inhibition mechanism was further discussed by DLVO theory. CTAB exhibited best performance among five surfactants. The swelling efficiency of kaolinite, halloysite and illite in DI water is 2.52%, 1.65% and 1.32% respectively, and these values can be reduced to 0.45%, 0.65% and 0.82% respectively in presence of single (NH4)2SO4. As (NH4)2SO4 was compounded with 0.04% CTAB, the swelling efficiency of kaolinite, halloysite and illite was further reduced to 0.25%, 0.45% and 0.31% respectively. The XRD and SEM analysis indicated that no change of the morphology and crystal structure of minerals after soaking with surfactants were presented. It was further clarified by DLVO theory that the London-van der Waals energy between clay particles increased, while both of the repulsion electrostatic energy and the total potential energy decreased in the presence of CTAB, and this was beneficial to the clay swelling inhibition.