Investigation on the Bakudi Bentonite Santhal Pargans, (Bihar), supplied by Messrs Calcutta Mineral Supply Co., Pvt., Ltd.

Abstract

This bentonite sample occurring near Bakudi and Tinpahar in Santhal Pargans (Bihar) had a brownish-grey colour. The sample was associated with an initial moisture content of 9.71 percent which was in agreement with the tentative specifications for “Western bentonite” of the Steel Founder’s Society of America. Chemical analysis on the sample showed the presence of silica and alumina in 41.66 and 26.43 percent respectively. Alumina content was high.TiO2 and CaO were also high. Alkalies, Na2O and K2O were 0.4 and 0.35 percent respectively.pH-value of 8.1 which was found to be below the minimum limit put down by the Steel Founder’s Society of America in their tentative specifications for “Western bentonites". Gel strength of the sample was only 10 percent which represented the approximate montmorillonite content of the sample. Swelling index of the bentonite was only 2.5 which showed it very low-selling characteristics. About 4% of the sample was retained on the 200 mesh and 16% on the 270 mesh sieves of the U.S. sieve series. In other words 79.72% of the sample had particle size less than 53 microns. Petrological examination of the sample showed it to be chiefly composed of microcrystalline aggregates and consisted of montmorillonite (several members of the group) among which beidellite was quite predominant. It was followed by traces of hydromice, calcite, opaque minerals and biotite. The bentonite had a total base exchange capacity of only 49.405 milliequivalents per 100 gms. Na/Ca ratio of the sample was 1.1622, which clearly showed it to be not of sodium base. As could be seen in the thermo gram(fig.1), the primary doublet peak recorded at a temperature of 160 °c with a range of 55-300°c, was quite characteristics of montmorillonite. There was a secondary endothermic peak recorded at a temperature of 575°c which did not show any definite conclusive characteristics.