Characterization and Cation Exchange Capacity (CEC) study of weathered granite profile from Lumut, Perak

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Date
2016-06
Authors
Siti Nuriha Mahmud
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Weathered crust of granite sediments from Lumut, Perak were analyzed for mineralogy, chemical composition by various analytical methods including x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray fluorescence (XRF) and inductively couple plasma (ICP-OES). The mineralogical and geochemical study was conducted according to weathered profile of granitic rocks which can be divided into A horizon (lateritic profile), B (weathered horizon) and C (sub-weathered horizon). The study addressed the distribution patterns and behavior of rare earth element (REE) in the sediment. Mineral composition of weathered samples is dominated by quartz, kaolinite and halloysite with minor amount of gibbsite and pyrophyllite. The whole chemical composition of weathered granite shows that the sediments rich in SiO2 but have low Al, Fe, Mg, Na, Ca and K contents. The chemical index of alteration (CIA) value ranged between 95 to 97% suggests an intense weathering at the source area. Therefore, it is observed that the enrichment of REE is in B horizon whereas A horizon and C horizon are depleted or less enriched in REE contents. Enrichment of REE in weathered sediments are likely corresponds to the high intensity of weathering. From the determination of cation exchange capacity (CEC) by using two different methods; ammonium acetate method and methylene dye blue test, it is reported that high values of CEC was found in the sample of A horizon, decreasing in B and the lowest in C horizon. The higher CEC value in A horizon instead of B could be particularly due to the abundance of clay minerals and soil organic matter.
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