Ecological Engineering 88 (2016) 10–19 Contents lists available at ScienceDirect Ecological Engineering jo ur nal home p ag e: www.elsevier.com/locate/ecoleng Green process using hot spring bacterium to concentrate alumina in coal ﬂy ash Sudip Kumar Sen a , Madan Mohan Das b , Partha Bandyopadhyay a , R.R. Dash b , Sangeeta Raut b,∗ a In Gene Research Lab. Biostadt India Limited, Waluj, Aurangabad, Maharashtra b Department Of Biotechnology,Gandhi Institute of Engineering Technology, Gunupur, Rayagada, Odisha a r t i c l e i n f o Article history: Received 27 May 2015 Received in revised form 20 November 2015 Accepted 3 December 2015 Keywords: Coal ﬂy ash Bioleaching Hot spring bacteria Alumina Silica sol a b s t r a c t The disposal of ﬂy ash as a by-product of incineration of coal is a more signiﬁcant problem than ash produced from burning of municipal solid wastes, sugarcane bagasse, rice husks or tea dusts because of its volume. The present investigation aims at upgrading alumina in coal ﬂy ash (CFA) through bioleaching, using Bacillus barbaricus (silicate bacterium) isolated from Taptapani hot spring, Odisha. Bioleaching has been done after washing CFA (WCFA) with water and the result obtained is compared with the results obtained by bioleaching of unwashed CFA (UCFA). The concentration of alumina in washed coal ﬂy ash has increased to 34.72% from an initial concentration of 25.45% after 60 days. The residue also shows a reduction of silica content from an initial concentration of 62.14% to 40.71% after 60 days. All the experimental results are corroborated with chemical analysis as well as through characterization process. Thus present ﬁnding has opened an avenue for enrichment of CFA with respect to alumina which may be suitable for aluminum extraction. In addition, by-product may be used for production of silica sol. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Nowadays there has been increased risk regarding the availabil- ity of aluminum due to the depletion of bauxite ore. There has been urge for upgrading the ore for proﬁtable extraction of aluminum by usual routes of chemical processing (Meyer, 2004). Among other processes of concentration, bioleaching is a suggested method for up-gradation of low and lean grade ores (Meyer, 2004). Fly ash is one of the wastes obtained from thermal power plants and contains 24-25% of alumina and 63-64% of silica in it. In India, the amount of ﬂy ash generated at present is approximately 150 million tons per annum. The management of ﬂy ash produced by coal ﬁred power plants is considered to be a major problem in many parts of the world (Polic et al., 2005). Fly ashes have been applied in composite cements (Escalante-Garcia et al., 2006; Escalante-Garcıa et al., 2008), as a support for catalysts (Flores et al., 2008), as raw material for the recovery of highly valued metals (Navarro et al., 2007; Font et al., 2007) in concrete (Osorio, 2007), in silica extrac- tion (Moreno et al., 2002) and in low Si/Al zeolite synthesis (Font ∗ Corresponding author at: Department of Bio-Technology, Gandhi Institute of Engineering and Technology, Gunupur.765022, Odisha, India. E-mail address: research.sangeeta@gmail.com (S. Raut). et al., 2009). Utilization of such waste material for preparation of beneﬁcial products in larger quantities is an active area for present day research in the world. In the Bayer process, bauxite is digested by washing with a hot solution of sodium hydroxide, NaOH, at 175 ◦ C, under pressure. This converts the aluminum oxide in the ore to soluble sodium aluminate, 2NaAlO 2 , according to the chemical equation: Al 2 O 3 + 2NaOH + 3H 2 O → 2NaAlO 2 This treatment also dissolves silica, but the other components of bauxite do not dissolve. For bauxites having more than 10% silica, Bayer process becomes infeasible due to insoluble sodium aluminum silicate being formed, which reduces yield, so another process must be chosen. Therefore if Bayer process is tried to con- centrate alumina from ﬂy ash, it will be a futile attempt because of presence of high amount of silica (∼ 62%) in ﬂy ash which will interfere in the process of digestion of alumina from ﬂy ash. There is slow dissolution of reactive silica present in the ﬂy ash. This reac- tion occurs both at high and low pH, resulting in the formation of silicic acid as shown below. SiO 2 + 2H 2 O → H 2 SiO 4 - + 2H - Therefore, bioleaching is proposed to be an alternative process for up-gradation of alumina in the coal ﬂy ash (CFA). Fortunately, http://dx.doi.org/10.1016/j.ecoleng.2015.12.012 0925-8574/© 2015 Elsevier B.V. All rights reserved.