Mineralogical characteristics of bentonites occurring in Ningcheng and Jianping area, China

Abstract

This study is focused on the basic mineralogical and chemical characteristics of some selected samples from Jianping (JP) and Ningcheng (NC) area, China. These were studied using X-ray diffraction (XRD), expandability, Greene-Kelly test, specific surface area, cation exchange capacity (CEC), differential thermal analysis (DTA), and chemical analysis. The bulk samples consist of mainly montmorillonites along with appreciable amounts of cristobalite and with small amounts of quartz, feldspar and calcite. The basal spacings of montmorillonites in all these examined samples show at about 1.5 nm, indicating that predominant cations were divalent. Mean crystallite thickness of the present sample lies from 0.449 to 0.710 nm (4.58–7.24 layers). As Greene-Kelly test, samples from Ningcheng area confirmed appreciable amount of beidellite component but samples from Jianping area did not contain anything about it. Surface area of samples varies from 671 to 766 m2 g−1 depending on the amounts of impurities. Analyzed CEC ranges from 70.30 to 82.75 meq 100g−1 in < 2 μm size samples. The DTA curves are considered abnormal type. Samples from Ningcheng area show relatively higher amount of SiO2 than those from Jianping area, possibly due to difference of parent rock type. Trace element (Y, Nb, Ce and Zr) data are plotted on acidic to intermediate composition. It is apparent that no large chemical transfer would have been necessary during alteration.