Abstract—Microbial depyritization of coal using chemoautotrophic bacteria is gaining acceptance as an efficient and eco-friendly technique. The process uses the metabolic activity of chemoautotrophic bacteria in removing sulfur and pyrite from the coal. The aim of the present study was to investigate the potential of Acidithiobacillus ferrooxidans in removing the pyritic sulfur and iron from high iron and sulfur containing US coal. The experiment was undertaken in 8L bench scale stirred tank reactor having 1% (w/v) pulp density of coal. The reactor was operated at 35ºC and aerobic conditions were maintained by sparging the air into the reactor. It was found that at the end of bio-depyritization process, about 90% of pyrite and 67% of pyritic sulfur was removed from the coal. The results indicate that the bio-depyritization process is an efficient process in treating the high pyrite and sulfur containing coal. Keywords—At. ferrooxidans, Batch reactor, Coal desulfurization, Pyrite. I. INTRODUCTION HE combustion of coal for power generation is known to cause environmental damage in the form of acid rain and emission of sulfur dioxide [1]. The sulfur dioxide caused formation of sulfate aerosol, lead to respiratory illnesses, whereas acid rains cause serious damages to the building material, biota and natural ecosystems. The emission of sulfur- dioxide and acid rain is due to the combustion of sulfur present in the coal. Sulfur present in variety of coals largely in three forms: pyritic, organic and sulfate sulfur. The sulfur associated with organic matter is the integral part of the coal matrix, whereas pyritic sulfur present in coal as mineral matter. The pyritic sulfur is generally present in highest concentration in most of the coals. The heterogenous nature and varied mineralogical composition makes it difficult to demineralize the coal prior to its combustion. The removal of pyritic sulfur prior to combustion is an effective way to ensure environmental clean combustion of coal. Various physical and chemical methods have been tested to remove the sulfur from coal by floatation, oxidation and reduction with chemicals [2]. Dr. Ashish Pathak is a Post Doctoral Research Fellow at Mineral Resource Research Division, Korea Institute of Geoscience and Mineral Resources, Gwahang-no 124, Yuseong-gu, Daejeon, 305-350, South Korea (e-mail: ashishpathak05@gmail.com). Dr. Dong Jin Kim* and Dr. Byoung-Gon Kim are Principal Researchers at Mineral Resource Research Division, Korea Institute of Geoscience and Mineral Resources, Gwahang-no 124, Yuseong-gu, Daejeon, 305-350, South Korea (e-mail: djkim@kigam.re.kr bgkim@kigam.re.kr). H. Srichandan is a Research Assistant at Mineral Resource Research Division, Korea Institute of Geoscience and Mineral Resources, Gwahang-no 124, Yuseong-gu, Daejeon, 305-350, South Korea and also a PhD student at Chungnam National University, Daejeon, 305-764, South Korea (e-mail: buna.biot@gmail.com). However, the physical methods suffer problems such as loss of a major portion of coal and inadequate removal of mineral matter embedded in the matrix. On the other hand, the chemical methods employed were found efficient in removing sulfur from coal but they produce secondary waste products and also affect structural integrity of the coal [3], [4]. Therefore, research interest has been shifted to biological depyritzation processes which offer a clean and economical alternative to remove sulfur from coals. In biodepyritization process, microbes catalyze the biochemical reactions resulting in oxidation and conversion of insoluble pyrite sulfur into soluble sulfate [5]. The chief microorganisms used in biodepyritization process are chemoautotrophic mesophilic bacteria such as Acidithiobacillus ferrooxidans (At. ferrooxidans) and Acidithiobacillus thiooxidans (At. thiooxidans) [6], [7]. The process has also been conducted using thermophilic microorganisms. However, thermophilic process is not preferred due to the high energy cost associated with it. In recent years, researchers have attempted to utilize the efficiency of chemoautotrophic microorganisms [8]-[10] in depyritization of coal. These studies have reported the effect of solids concentration, particle size, type of microbes etc. on the efficiency of biodepyritization process. Though, the process has been fairly investigated, most of these studies were conducted in shake flasks and results varied due to the different experimental conditions and types of coal employed. Therefore, for development of an efficient and economical biodepyritization process more in-depth studies are required. The aim of the present study is to remove pyrite and pyritic sulfur from coal having high sulfur and iron content. The study was undertaken in 8 L working batch stirred reactor by employing At. ferrooxidans and using US coal. II. MATERIAL AND METHODS A. Coal Sample The coal sample was procured from Eagle river coal LLC, Harrisburg, Illinois, US. The coal was first crushed into small pieces by Jaw crusher followed by grinding into small particles by pulverizer. The pulverized coal particles were subjected to vibrating cup mill for grinding to obtain the desire particle size (100-200μm). The physical and chemical properties of the coal used in the present investigation are presented in Table I. Depyritization of US Coal Using Iron-Oxidizing Bacteria: Batch Stirred Reactor Study Ashish Pathak, Dong-Jin Kim, Haragobinda Srichandan, Byoung-Gon Kim T World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:7, No:11, 2013 839 International Scholarly and Scientific Research & Innovation 7(11) 2013 scholar.waset.org/1307-6892/9996567 International Science Index, Environmental and Ecological Engineering Vol:7, No:11, 2013 waset.org/Publication/9996567