This study aimed at finding out whether the property of plasticity of acid leached clays can be reversed by treatment with a suitable base. Studies were carried out on representative samples, which were taken from iron bearing clays from Mukurwe-ini, Nyeri County in Kenya (Latitude 00°34´00´´S, Longitude 37°03´00´´E). Characterization of the clay was done in its natural form, and after acid treatment, to determine its mineralogical and chemical composition. Natural clay was refluxed with sulphuric and hydrochloric acids of different concentrations at 100 and 200°C for 2 h followed by thorough washing with distilled water to remove the acid matrix. Atomic absorption spectroscopy, X-ray fluorescence spectroscopy, and X-ray diffraction, analysis techniques were used to determine the physico-chemical characteristics of natural and acid leached clays. The results indicate that SiO2, Al2O3, and Fe2O3 are the major components of Mukurwe-ini clay, MgO, CaO, K2O, TiO2, MnO, and Na2O are present in trace amounts. XRD characterization shows that Mukurwe-ini clays consist primarily of quartz, kaolinite, albite, and microcline minerals. Iron content was drastically reduced in the acid washed samples and X-ray diffraction (XRD) mineralogical analysis of base acid-activated clays showed enhanced levels of the mineral kaolinite in comparison to acid-activated clays (5.3 to 15.7%) a clear indication that the natural properties of the acid washed clay were restored by base treatment of acid washed samples. The Atterberg limits of the base treated samples closely compared with those of the natural clays.
Key words: Clay minerals, Atterberg limits, and plasticity.