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MULTISTAGE CAUSTIC LEACHING DE-ASHING OF NIGERIAN LAFIA-OBI COAL

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Author(s): A. A. Adeleke | S. A. Ibitoye | A. A. Afonja | M. M. Chagga

Journal: Petroleum and Coal
ISSN 1337-7027

Volume: 53;
Issue: 4;
Start page: 259;
Date: 2011;
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Keywords: coal | ash | de-ashing | leaching | concentrate.

ABSTRACT
Fractions of the high ash Nigerian Lafia-Obi coal L±250 ground to pass the 250 μm sieve in threestages were subjected to proximate/ash composition analyses, hot aqueous leaching de-ashingwith water and sodium carbonate in multiple stages and in a H2O-Na2CO3-H2O sequence (withinitial solution homogenization). The results obtained showed that ash contents percent of 24.60,14.70 and 24.07 were obtained for fractions L-250(1), L-250(2) and L+250(2); respectively asagainst 32.55% in the as-received coal. The ash reductions obtained translate to overall averageash removal of about 38.66% at the 19.90% ash content of the concentrates blend at a good 1:20ratio of reagent to coal. The study also showed that a three stage leaching in the sequence H2ONa2CO3-H2O (HSH) produced a higher leaching rate than Na2CO3-H2O-H2O (SHH). The ash contentof the concentrates blend at 19.90% is lower than 23.80% required for coal blends for Indianstandard coking practice, but higher than the maximum of 10% upper limit for the conventionalcokemaking practice. The reduction in ash content obtained at the atmospheric pressure treatmentof Lafia-Obi coal was found to compare favourably with that of a high pressure elevated temperatureautoclave leaching of an Illinois coal. Binary blend formulation between the prime coking westernCanada coal and Lafia-Obi coal as-leached showed that inclusion of 16.63% of the latter wasprobable and this translates to reduction in cost per ton of about $23.67. A successful upgrade ofthe leaching route derived to industrial scale will make Lafia-Obi coal available as a blend componentfor economical cokemaking.
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