R. K. Fowler’s research while affiliated with The Ohio State University and other places

Greenhouse column studies of 8 mo duration investigated the solubility and mobility of salts and trace elements in dry flue gas desulfurization (FGD) by-products used for minespoil reclamation. Three mine-spoils were amended with two dry FGD by-products (lime injection multistage burners ash, LIMB; and, pressurized fluidized bed combustion ash, PFBC) using amounts from 0 to 320 g kg -1. Two of the minespoils also received sewage sludge amendment of 60 g kg -1. Columns were planted with 'Kentucky 31' tall rescue (Festuca arundinacea Schreber). Leachate analyses and pH determinations from column mixes were done at the beginning and the conclusion of the experiments. Both FGD by-products were effective in raising pH of the spoil materials. The largest LIMB amendment raised pH to near 12 and resulted in the formation of ettringite [(Ca 6Al 2(SO 4) 3(OH) 12 · 26 H 2O)]. Leachate pH, electrical conductivity, dissolved organic C, Ca, Mg, and S tended to increase with increased FGD amendment, while Al, Fe, Mn, and Zn decreased. Changes in leachate As, B, Cu, Ni, and Se depended on interactions among the type of FGD, the type of spoil, and the presence of sewage sludge, with pH being the most important variable. Overall, with FGD amendments of 120 g kg -1 or less, leachate concentrations of most elements of environmental concern were less than drinking water standards. The amount of FGD by-product that can be applied to a minespoil is probably limited by soluble salts and initially high pH levels rather than by trace element loading of spoil or water.

Characterization studies of PFBC by-products were initiated to provide baseline information need to predict the behavior and suitability of PFBC by-products for beneficial uses. The chemical composition of the by-products was dominated by Ca, Mg, S, Fe, Al, and Si. All samples were highly alkaline with paste pH values ranging from 9.9 to 12.3. All of the PFBC materials met the criteria for pollutant ceiling concentrations for land application of sewage sludge for Cd, Cr, Cu, Pb, Mo, Ni, Se, and Zn. Arsenic exceeded the concentration ceiling level in only one sample. XRD results showed that the cyclone ashes consisted primarily of dolomite, anhydrite, periclase, and calcite. PFBC bed ashes were similar in composition but contained less unspent sorbent and more, anhydrite and periclase. The artificial weathering study examined water soluble ions and reaction products of two mine spoils and one cyclone ash mixed at four rates. The spoils were mixed with PFBC by-products to yield mixtures containing 0, 10, 20, and 40 weight percent by-product. Leachate composition was mostly a function of rate of application and equilibration time. In general, the addition of PFBC by-product increased pH, conductivity, and the concentrations of Ca, K, Mg, Mo, Na, S, and Sr. The concentrations of Al, Fe, and Mn decreased. Six metals (Ag, As, Ba, Cd, Cr, and Pb) regulated by the Resource Conservation Recovery Act were below concentration levels defined for drinking water standards (Hg and Se not available). All application rates of the PFBC by-product increased the solution pH significantly. A pH of 7.8 or greater was attained in all PFBC-spoil mixtures after 132 days. Changes in solid phase composition were independent of the spoil. The final reaction products were more directly influenced by the characteristics of the PFBC by-product.