Mineral Resources Potential - Geothermal Resources

43 Bentonite
Industrial Minerals 129
Bentonite is an absorbent aluminium, generally impure clay
consisting of phyllosilicate mostly of montmorillonite, (Na,
Ca)3(Al,MghSi40 dOH)z*nH20 with several other types. Two
types exist: swelling bentonite, which is also called sodium
bentonite, and non-swelling bentonite or calcium bentonite. It
forms h m weathering of volcanic ash, most often in the presence
of a water body. Bentonite expands when wet-sodium bentonite
can absorb several hundred % of its dry weight in water
(Noetstaller, 1988).
Applications
It is commonly used in drilling fluids. used to make slurry walls,
and to form impermeable barriefs (i.e. plug old wells, as a linerin
the base of landfills to prevent migration of leachate into the soil);
several other minor uses (medicine, agriculture, etc.) also exist.
Bentonite is used as absorbent, animal. feed, foundary sand,
catalyst (oil refining), waterproofing and sealing, etc. (Noetstalier,
1988).
Bentonite deposits in Ethiopia
Huge deposits of bentonite occur in the Afar region at several sites
(e,g. Wakisa Mi, Gewme area, Hararghe) and at Gidicho Island
(Lake Abaya) in Sidarno. In the Afar region, the total resources
have been estimatsd at 170 Mt of bentonite (EGS, 1989). The
chemical composition is in the range of 5040% silica, 11-14 %
alumina, 7-9% iron and less than 1.3% sodium and potassium
(Mengistu and Fentaw 2000). The deposits are part of the thick
sequence of lacustrine and reverine clays, silts sands and
calcareous grits, grad conglomerates and Mites interbedded with
basalt and ash beds. The sediments were deposited near the
western margin of the southern part of Afai Depression which