Characterization of two low-charge vermiculites after hydrochloric acid treatment

Abstract

Two natural vermiculites (Ver) with very similar chemical composition but slightly different low charge on the layers were investigated to find an answer the question, how to change their structural and chemical properties after exposure to different concentrations of HCl solutions. Vermiculite from Bulgaria (Ver-B) with the layer charge 0.47 eq/O10(OH)2 and from Brazil (Ver-SL) with the layer charge 0.36 eq/O10(OH)2 were studied on their particle size fraction less than 40 μm after treatment at different HCl concentrations (0.5 M HCl and 1 M HCl). Both samples represent a mixed-layer structure after incomplete transformation of mica (biotite) to vermiculite. Based on the XRD patterns, Ver-B may be considered as the mixed-layer vermiculite interstratified with small proportion of mica layers and Ver-SL as the mixed-layer mica-vermiculite. The leaching with 0.5 M HCl increased SA of Ver-B from 29.5 m2.g-1 to 261 m2.g-1 at Ver-B05 in comparison with the SA of Ver-SL from 14.0 m2.g-1 to 191 m2.g-1 in Ver-SL05. It can be assumed that the acidification was more effective to: (1) leaching of Mg2+ cations at incomplete vermiculated sample Ver-SL and (2) Fe2+and Fe3+ from octahedra and Al3+ from the tetrahedra at vermiculite sample Ver-B and (3) increasing SA at Ver-B.