Investing in Ethiopia’s industrial minerals – Bentonite

m i n i s t r y o f m i n e s a n d e n e r g y f e d e r a l d e m o c r a t i c r e p u b l i c o f e t h i o p i a

introduCtion

Bentonite is a fine-grained clay consisting essentially of minerals of the smectite group. Because of their chemical composition, individual smectite crystals are negatively charged, and electrical neutrality is maintained by ‘exchangeable’ cations located mainly between the clay crystals. The structure, chemical composition, exchangeable ion type and small crystal size of smectite are responsible for several unique properties, including a large chemically active surface area, interlamellar surfaces having unusual hydration characteristics, and the ability to modify strongly the flow behaviour of liquids. These properties form the basis for the wide range of uses for bentonite by industry (see backpage).

Most of the world’s largest commercial bentonite deposits formed by alteration of fine-grained volcanic debris which was deposited over relatively large areas. Other bentonites have formed by in situ hydrothermal alteration of coarser igneous rock.

World production of bentonite is currently approaching 17 000 million tons per year, with the USA by far the largest single producer at 7600 Mt/yr. Other major producing countries are Greece and Turkey (both 900–1000 Mt/yr), and Japan, Germany and Mexico (400–500 Mt/yr). The largest single use of bentonite is in foundry moulding sand (24%), followed by drilling mud (21%) and iron ore pelletizing (15%). Various absorbent uses together account for a further 23% of world production.

Bentonite aPPLiCations

Foundry moulding sands: Sand is mixed with bentonite and water so that it can be formed round a pattern. When this pattern is removed, hot metal is poured into the mould (bottom photograph).

Drilling muds: Dilute suspensions of bentonite lubricate and cool the drilling bit, help bring rock cuttings to the surface, and seal the walls of the hole. They also carry weighting media such as baryte or hematite to balance high hydrostatic pressures in the drill holes.

Absorbent: Granular bentonite is used as an industrial absorbent and also as pet litter.

Iron ore pelletizing: Used to bind fine-grained iron ore into pellets prior to loading into the blast furnace (middle photograph).

Civil engineering: Bentonite slurries seal porous strata and stop water movement in foundations for buildings, tunnels and dams.

Food treatment: Bentonite removes colour and impurities from edible oils, fats and beverages. It is usually activated with acid to improve effectiveness (top photograph).

Agriculture: Used as a carrier for insecticides and pesticides, as a binder for fertilizers and as a coating for seeds.

LaBoratorY testing

Examination by X-ray diffraction provides definitive information on the exact species of smectite mineral present in the bentonite, as well as the presence or absence of non-clay impurities such as calcite, gypsum and cristobalite which can affect the commercial performance of the clay. Chemical analysis, particularly determination of cation-exchange capacity, provides a reliable preliminary indication of suitability for different applications. Measurement of physical properties such as the free-swelling volume in water and plasticity, especially following addition of small quantities of sodium carbonate, provides further evidence of suitability for specific applications. However, determining whether a bentonite meets specifications for particular applications requires specialist equipment such as viscometers and pressure filters (for drilling muds), impact and compressive strength apparatus (for foundry moulding sands and pelletizing) and acid-reflux apparatus and spectrophotometers (for bleaching oils). Bentonite in ethioPia

Bentonitic clays have been identified in two main areas of the Ethiopian rift valley. At Ledi, Warsissa and Gewane (top three localities on map below) they occur as part of a thick sequence of a Tertiary to Quaternary lacustrine sediments consisting of clays, silts, sands, calcareous grits, conglomerates, basaltic flows and ashes. Resources

have been estimated at 170 million tons. Bentonitic clay of Pleistocene age occurs at Gidicho Island (bottom locality on map below), Lake Abaya, in association with diatomite, with a total estimated resource of five million tons.

Although testing of bentonitic clays from these localities has indicated suitability for drilling mud, iron ore pelletizing and, possibly, foundry use, apart from minor and sporadic exceptions, these deposits have not been worked to provide material for use by local industries. Essentially all bentonite used within Ethiopia is imported, material coming from a range of countries (see table overleaf).

The main use of this imported bentonite is in processing of edible oil. Other outlets are in drilling, metal casting and for filtering beer. Currently there are numerous small-scale edible-oil producers who do not bleach their products, but forthcoming Government regulations may make this mandatory. This should lead to an increase in demand for bleaching-grade bentonite.

regionaL markets and trade

Of the countries in the immediate region, Egypt and South Africa produce significant amounts of bentonite for their own use, with South Africa also being a large importer (15 000 tons in 2005). In 2002, Sudan imported 3200 tons. However, regional demand is dominated by the Kingdom

ADDIS ABABA

AWASA

GOBA

AWASH

DESSIE Rift fault

Precambrian faults & shear zones

Town

Known bentoniteoccurrence

Distribution of bentonite occurrences in Ethiopia.

Contacts Geological Survey of EthiopiaIndustrial Minerals Exploration DivisionPO BOX 2302Addis Ababa, Ethiopia tel: [251 11] 646 33 25fax: [251 11] 646 33 26email: survey@telecom.net.etwww.geology.gov.et

of Saudi Arabia at a yearly consumption of up to 70 000 t/yr, mainly for drilling muds. Bentonite is an internationally traded commodity, and there will always be a market for material that is price-competitive and can meet relevant specifications, particularly those of the American Petroleum Industry for drilling muds.

Further sourCes oF inFormation

Reports on geological exploration for bentonite in Ethiopia can be obtained free of charge from the Geoscience Information Centre at the Geological Survey of Ethiopia. Staff of the GSE can also provide information on bentonite imports, users within Ethiopia, and detailed specifications for different uses. The Central Geological Laboratory of the GSE is able to carry out evaluation tests on specific materials and recommend suitable processing flowsheets for different applications.

imPorts oF Bentonite, 2000-2005

Year 2000 2001 2002 2003 2004 2005

tons 268 238 111 26 167 169

us $ 66797 68829 26421 7224 32952 49158

us$ per ton 249 289 237 278 197290

Country of origin

ItalyChinaGermanyNetherlandsSaudi Arabia

ItalyUKChinaNetherlandsUAE

EgyptNetherlandsItalyChinaSouth Africa

ChinaPakistan

IndiaChinaUAEBelgium

ChinaUSAUKPakistan