Coal is an important source of energy and plays an important role in the cement manufacture in the country. It is estimated the 70% of the Indian coals are of inferior grade with high ash content. The Indian coals in general are of higher ash content , typically the calorific value of 3400-4800 cal/g with ash content ranging between 20 -50%.
The Cement clinker manufacture with use of such high ash coals, along with the available marginal limestone deposits necessitates higher consumption of high grade limestone , availability of which is scarce in the country.
This necessitates beneficiation of the high ash coal. Conventional methods like washing for coal beneficiation are generally the method used which generates an appreciable quantum of higher ash containing middlings and rejects which require to be suitably used.
Use of Biotechnological methods for beneficiation of coal has created newer opportunities and challenges. In one of the short term exploratory work carried out at the laboratory attempts were made to assess the possibility of bio-leaching of the ash in high ash coals , through the use of silica leaching bacteria isolated from cement Raw Materials such as Limestone, Dolomite, Coal , Iron ore etc . The bacteria belonging to the Thiobacillus species such as Thiobacillus thiooxidans , Thiobacillus ferroxidans and Bacillus Circulans . The findings of this short term exploratory project were very encouraging, although the research activity could not be subsequently pursued at the authors laboratory.
The paper discusses the experimental data generated at authors laboratory related to isolation and development of cultures (Thiobacillus and Bacillus species) , type of media for bio leaching of ash in coals with varying ash contents of 35 – 45% .
The paper discusses the experimental results , which indicated a reduction of ash content by 15 – 18 % , the ash reduction being dependent on the type of media used , and incubation time and the type of bacteria species .The authors also attempted to correlate the reduction of ash content with soluble silica content in the leachates with time . Based on the observations the authors conclude that the bio beneficiation route has a high potential . The Paper was presented and published at 10th NCB Int Seminar