35 J. Indian Chem. Soc., Vol. 95, January 2018, pp. 35-40 Bentonites for chemical industries † Ashok Kumar Jha University Department of Chemistry, T. M. Bhagalpur University, Bhagalpur-812 007, Bihar, India E-mail : ashokjha39@gmail.com Manuscript received 28 November 2017, accepted 20 December 2017 Abstract : Bentonite deposits of major importance occur in association with volcanic rocks, tuffs and tuf- faceous sediments of Miocene and Oligocene age, The bentonite layers and veins indicate the bentonization of the tuff having 1–2 mt thickness of the beds. The chemical composition of bentonites are SiO 2 (50–60%), Al 2 O 3 (17%), Fe 2 O 3 , FeO, MgO, CaO, Na 2 O, K 2 O and traces of TiO 2 and cation exchange capacity value of bentonites are around 98 meq/100 g. Due to the presence of exchangeable cations, the important applica- tions are decolourising oil, manufacture of catalyst, production of oil well drilling muds softening of hard water and suitability of decontamination of radioactive wastes. Bentonites have been found a good adsorbent of hexavalent chromium and arsenic up to permissible limit. Maximum removal of Cr VI takes place at 120 mt. First order kinetics is followed in the case of adsorption of Cr VI and As III by bentonites. This can be exploited on large scale in industry for decontamination of water pollutants. In view of individual properties, characterization of bentonite has been done using PXRD, TGA, DSC and IR studies. In the OH-stretching region obtained from FTIR, the bands (3600–3690 cm –1 ) represent sur- face OH and inner OH. Investigations on thermal behaviour presented a total weight loss of 14.4953%, 19.2160%, 9.8243% and 3.6774% for different samples showing loss of molecular water and dehydroxylation. The PXRD analysis important for the clay minerals make understand the diffraction characteristics of bentonites. The proportion of montmorillonite layers is abundant in the inner part, but at the margin the layers of Kaolin are present shown in RHB 5 , RHB 6 , RB 8 , RB 9 and RB 10 samples. The chemical formula has been obtained as (Na,Ca) 0.3 (Al,Mg) 2 SiO 4 O 10 (OH) 2 .nH 2 O unit indicating mont- morillonite. Keywords : Bentonite, PXRD, TGA, adsorbent, cation exchange capacity. Introduction Geological formation Bentonite deposits of major economic importance occur in association with volcanic rocks, tuffs and tuffaceous sediments of Miocene and Oligocene age. The genesis of the deposits is from : (i) Alteration from rhyolitic ash in a marine en- vironment. (ii) Hydrothermal alteration from rhyolite and rhyolitic tuff. It appears that much of the silica and alkali was † Invited Lecture delivered at the 54th Annual Convention of Chemists (2017), organized by the Indian Chemical Society held at Uka Tarsadia University, Maliba Campus, Bardoli, Surat, Gujarat during December 23-25, 2017 leached from the tuff and other rocks by solution during alteration. The rocks fragments are entirely altered to clayey materials exhibiting a deep bluish-green colour, be- comes gray to black in day light within 1 h. It turns brown within a few weeks 1–3 . The fragments are usually brown in colour on exposed surfaces in the field. The thickness of bentonite bed mined is 1–2 m. The blue colour with benzidine solution indicates the presence of montmorillonite unit 4 . The chemical formula of montmorillonite is