There is great interest in returning coal combustion products to mining sites for beneficial reuse as liming agents. A column study examined the effects of blending two coal fly ashes with an acid-forming coal refuse (4% pyritic S). Both fly ashes were net alkaline, but had relatively low neutralizing capacities. One ash with moderate alkalinity (CRF) was bulk blended with coal refuse at 0, 20, and 33% (w/w), while another lower alkalinity ash (WVF) was blended at 0, 5, 10, 20, and 33% (w/w). The columns were leached (unsaturated) weekly with 2.5 cm of simulated precipitation for >150 wk. Where high amounts of ash alkalinity (>20% w/w) were mixed with the coal refuse, pyrite oxidation was controlled and leachate pH was >7.0 with low metal levels throughout the study. At lower rates of alkalinity loading, trace metals were sequentially released from the WVF ash as the 5, 10, and 20% treatments acidified due to pyrite oxidation. Lechate metals increased in proportion to the total amounts applied in the ash. In this strongly acidic environment, metals such as Mn, Fe, and Cu were dissolved and leached from the ash matrix in large quantities. If ash is to be beneficially reused in the reclamation of acid-producing coal refuse, the alkalinity and potential acidity of the materials must be balanced through the appropriate addition of lime or other alkaline materials to the blend. Highly potentially acidic refuse material, such as that used here, may not be suitable for ash/refuse codisposal scenarios.

The exclusion of coal fly ash from regulation as a hazardous waste has led to increased interest in returning ash to the coal fields for disposal. Bulk blending alkaline fly ash with acid forming coal refuse may present a disposal option that also aids in the control of acid mine drainage (AMD). A column leaching study was initiated to examine the leachate quality from acid forming coal refuse‐fly ash blends. Coal refuse alone (2.2% total S), and bulk blended coal refuse and alkaline fly ash (20 and 33% ash, w/w) were packed into 20‐cm diameter leaching columns and run under unsaturated conditions for over 4 yr. Leachates were analyzed for pH, electrical conductivity, Fe, Mn, and SO2−4 content. The coal refuse columns acidified quickly and produced leachates that, at peak levels, contained high contents of acidity (pH 1.6), Fe (10 000 mg L−1), SO2−4 (30 000 mg L−1), and Mn (300 mg L−1). The high levels of metals in these leachates decreased over time. The ash‐treated columns maintained leachate pH values near 8.0 with very low metal levels. The bulk mixing of alkaline fly ash and coal refuse, at high blending rates (>20%), appears to an effective codisposal option that also provides long‐term AMD control. Only B and SO2−4 appeared to leach at any significant level and the quality of leachates from the ash‐treated columns was significantly improved with respect to the untreated coal refuse.

Abstract. Most Appalachian coal refuse materials contain significant amounts of pyritic S and are likely to produce acid mine drainage (AMD). A column technique was designed and implemented to evaluate the effects of various AMD mitigation treatments including fly ash, topsoil, lime, and rock-P. Two types of fly ash were tested, one at four rates of application, the other at two rates. Conventional lime plus topsoil, lime without topsoil, topsoil only, topsoil with fly ash, rock-P, rock-P plus topsoil, and rock-P plus fly ash were also evaluated and compared with pure refuse controls. The drainage from the unamended columns rapidly dropped to less than pH 2 with very high levels of Fe, Mn, and S. Alkaline fly ash dramatically reduced drainage Fe concentrations as well as Mn and S when compared with untreated refuse. The lime treatments also improved the drainage Fe, Mn, and S concentrations. The rock-P treatment initially reduced Fe, Mn, and S, but eventually lost its mitigation capability. Leachate B concentrations were initially high for some of the ash columns, but decreased over time, while the unamended refuse B levels increased with time. Combined treatments of phosphate/ash, ash/topsoil, and pure refuse with topsoil were intermediate between the pure ash treatments and unamended refuse in drainage quality. With further analysis, fly ash may prove to be a viable alternative to conventional topsoiling/lime treatments to ameliorate AMD if adequate alkalinity is present in the ash/refuse mixture. If fly ash alkalinity is inadequate to balance potential acidity, accelerated leaching of ash bound metals may occur.Additional Key Words: rock-phosphate, acid-base accounting, potential acidity, calcium carbonate equivalence.

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Sintering of 25-02-12 mol% Ce02 was accelerated by microwave processing at 2.45 GHz as compared with conventional firing. However, the size of the "microwave effect" was significantly smaller than that which was previously observed for microwave sintering of ZrO2-8 mol%. Y2O3. The difference in the effect that the microwave field had on the two zirconia systems is interpreted in terms of their ionic conductivities.