Dispersion and Upgradation of Limestone from new Umrangshu, Assam, India

Abstract

North Cachor district of Assam, India is endowed with a vast deposit of limestone at New Umrangshu (25°31'51" to 25 '32'8" N latitude and 92°48'1" to 92 °48'7" E long-itude). The deposit contains about 116 million tones of limestone extended over an area of 3.5 square km, which is used presently for manufacturing cement. The limestone contains over 91% CaCO3 (— 51-52% CaO) with —2.1-2.7% MgO, —1.5-2.2% Si02 and —0.8-0.9% A1203 mostly in the form of calcite with small to trace amounts of impurities like kaolinite, pyrite, illite. It was earlier reported that size classification leads only to marginal improve-ment of the limestone. The coarser fraction contains the maximum amount of CaO and minimum amount of Si02, A1203 and Fe203,. whereas, the fine fraction contains the mini-mum amount of CaO and maximum amount of SiO2 and Fe,03. The impurities are evenly distributed in the limestone. The present communication reports the results of further works carried on beneficiation of the limestone. Fine grinding leads to liberation of the clay minerals; the major impurities of the limestone which may be removed by adopting dispersion-cum-settling technique resulting a fraction containing —97% CaCO3 (54.3% CaO) with —0.5% SiO2 and —0.6% A1203