Project on Coal Combustion By-products for Use in Fertilizer Completed

The volume of flue gas desulfurization (FGD) by-products is expected to increase as use of the desulfurization materials increases because of continued stringent federal and state regulations requiring significant reductions in sulfur oxide and other pollutants, such as mercury. Additionally, the agricultural profile of Illinois is changing to meet the demand for more ethanol. Resultant changes in fertilization methods and crop rotation, coupled with environmental requirements to upgrade to clean burning coal systems, could link the agricultural and power generation markets in the state of Illinois if FGD can be used as a fertilizer additive. Previous studies have shown that treating manure with coal combustion by-products (CCBs) such as FGD can provide beneficial results in stabilizing manure phosphorus and increasing yields. Many of the studies have not considered the mineralogical and chemical composition of FGD by-products when mixed with manure and the possible environmental impact from the leaching of potential groundwater contaminants.

The main objective of this project was to characterize and compare samples from three separate coal plants in Illinois in order to investigate the chemical and mineralogical composition of different ratios of FGD to manure. Mineralogical properties of FGD samples were determined using x-ray diffraction methods. Chemical composition was determined by inductively coupled plasma mass spectroscopy and whole rock analysis–x-ray fluorescence methods after the FGD-manure mixtures were subjected to a standard test method for shake extraction of solid waste with water. When the samples were exposed to water, bassanite was converted to gypsum. Chemical analysis demonstrated that the ratio of FGD to manure can determine the concentrations of soil nutrients, such as phosphate or calcium, that would directly impact crop variables such as root growth, crop yield, crop health, or growth rates. The concentrations of aluminum, cadmium, cobalt, chromium, molybdenum, nickel, lead, antimony, and zinc in the 18-hour laboratory extracts were at or less than analytical detection limits. Arsenic was not detected in any of the extracts. Selenium was present, but in trace amounts near analytical detection limits. The FGD samples contained mercury at concentrations less than that required by the U.S. Environmental Protection Agency for classification as a low mercury waste for land-disposal restrictions. The reaction pH values of the sample mixtures suggested that potential groundwater contaminants would be relatively insoluble. Even with consideration of the chemical and mineral characteristics of the FGD-manure mixtures, it is still difficult to accurately predict environmental interactions in an open system, indicating additional work is needed before FGD-manure mixes can be applied in commercial agricultural practices.

The final technical report, entitled "Understanding the Nature of Coal Combustion By-products as Manure Fertilizer Additives," was submitted to the Illinois Clean Coal Institute.