English

Abstract

Research on the beneficial utilization of coal combustion products (CCPs) as surface amendments in mining environments has focused upon bulk acid-base balances and heavy metal (Cu, Zn, Fe, Al, Mn, etc.) mobility to local groundwater. Currently, the public and regulatory communities are placing greater focus on the potential of As, B and Se mobility from CCP utilization. Five CCPs were selected from a regional set of 28 materials following complete chemical characterization for greenhouse bioassay trials. Acidic sandstone mine spoil was amended at 0, 10, and 20% (v:v) with the CCPs. The bioassay trial was designed to test the presumed effectiveness of CCPs as surface-applied amendments to mine soils for improving pH and water holding capacity. The procedures were modified to include a “pour-through” protocol where we leached greenhouse pots with excess water starting one month after establishment of the trial, and then collected leachates for analyses of pH, EC, As, B, Se and other parameters. The trial was conducted using soybean (Glycine max) as an indicator plant sensitive to substrate chemical conditions (EC, pH, elemental toxicity) and tall fescue (Festuca arundinaceae) as a species exhibiting relative tolerance to low pH, metals, and salts. Tall fescue dry matter yield tended to increase with increasing CCP rate as long as the bulk soil pH remained at pH 8.0 or less. Depending on the liming capacity (as measured by calcium carbonate equivalence CCE) of the CCP applied, the 20% application had the greatest positive effect on plant yield (e.g. at CCE = 7.7). However, in case of a CCP with a high liming potential (CCE = 47.7), a 5% application was most beneficial to dry matter yield. The EC and pH from various mixes related well to CCE of the respective CCP and the loading rate. Leaching of oxyanion forming elements (As, Mo, Se) under these soil conditions and loading rates does not appear to be a concern, although some Se was observed in the first leachates. As expected, B along with S (as SO4 2) were the two elements at highest concentration in the leachates. However, correlation and stepwise regression analysis of yield data with the elemental concentrations from the pour-through solutions indicated these two elements did not negatively affect fescue yield. However, stepwise regression analysis did show that fescue yield was affected by pH (p > 0.0034). Our combined results indicate that a few relatively simple lab measurements (pH, EC, CCE) coupled with a simple soybean bioassay such as reported here can readily predict both the relative effectiveness and potential toxicity of a given CCP when used as either a bulk mine soil amendment or an alkaline additive for mine soil acidity control. Additional