Limestone

Hardness                       -         3 to 4 on Moh's Scale
Density                         -          2.5 to 2.65 Kg/m³
Compressive Strength    -           1800 to 2100 Kg/cm²
Water Absorption            -          Less than 1%
Porosity                        -           Quite low
Weather                        -            Impact Resistant
Lime (CaO)                     -         38-42%
Silica (SiO2)                  -           20-25%
Alumina (Al2O3)            -           2-4%
Other Oxides ( Na, Mg)  -          1.5 to 2.5%
Loss On Ignition (LOI)    -           30-32%

Specific gravity              -           2.91

 Refractive Index           -           1.51

Decomposition temp.     -           600 – 900 °C

 Brightness                    -           70 – 80

Limestone deposits are found in Ogun, Sokoto, Benue, Gombe, Cross-Rivers, Ebonyi, Kogi and Edo states. Consequently, cement factories in Nigeria are located at Ashaka, Yandev, Nkalagu, Shagamu, Okpilla, Ewekoro, Sokoto, Obajana and Calabar.

The limestone at Mfamosing, near Calabar, is the largest and the purest deposit in Nigeria. It is about 50m thick, at the quarry site. West of Calabar, another carbonate body occurs in the subsurface that is 450m thick. The Calabar flank is the main carbonate province in Nigeria, with well-developed tropical karsts and caves (Reiljers and Potters, 1987). The Mfamosing limestone has over 97 per cent limestone (CaC03).

The processing of limestone into hydrated lime is summarized as follows:

• Mined limestone is crushed into smaller units with jaw crushers and then fed onto vibrating screens.
• Crushed and screened material is weighed and conveyed into a hoist.
• It is then discharged into a vertical shaft or rotary kiln.
• Limestone is then thermally decomposed in the kiln at a temperature of about 800 – 1200⁰
• Quicklime is produced in the kiln and with the aid of conveyors, is transferred to a hammer mill/crusher for crushing
• Crushed quicklime is mixed with measured water/steam to get hydrated lime.
• The product is then moved into an aging tank, bagged, packed and marketed.

Hydrated Lime is one of the most extensively used industrial raw materials.  It is widely used in agriculture and buildings.  Its application in the chemical industries includes production of caustic soda, controlling of acidity, precipitated calcium carbonate production and for cement, fertilizers and rayons production.  It is also used for the production of calcium hypochlorite bleaches, citric acid, phosphate chemicals, glycerin and polypropylene oxide.

In the food industry, it is used in the softening of water and sugar refining, while in the building industry, it is effectively utilized in the manufacture of cement.

In metallurgical industries, it is used in the production of high grade steel, aluminum smelting and production of non-ferrous metals such as copper, zinc, lead, gold, silver and uranium.

Current national demand and supply is estimated at 155,000 tonnes and 54,000 tonnes/annum respectively, leaving a deficit of over 101,000 tonnes/annum.

Limestone and gypsum are the major raw materials in cement production. Nigeria, with an estimated population of 167 million people and a housing deficit running into millions, undoubtedly presents a huge market for investors in limestone exploration and processing. Investment opportunities also exist in metallurgical steel making, iron ore agglomeration, beneficiation of non-ferrous metals, manufacturing of caustic soda, fertiliser production, treatment plant, water and effluent treatment, pulp and paper: protective coating, white wash, masonry mortar, soil neutralisation and stabilisation, etc.