Masters Theses

Date of Award

5-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

M.E. Essington

Committee Members

J.T. Ammons, J.E. Foss, M. Mullen

Abstract

Surface mining allows pyrite to be brought to the surface, where it is readily oxidized, producing acid mine drainage. A feasible alternative for the reclamation of mine spoil is the utilization of lime-stabilized sewage sludge (LSS) and fly ash (FA). Lime-stabilized sewage sludge provides essential nutrients to assist in revegetation efforts in an otherwise deficient environment, provides organic matter to improve spoil physical characteristics, and provides a mechanism for disposal. Using a neutral FA in co-application with LSS can enhance mine spoil nutrient levels and physical characteristics. The University of Tennessee, Tennessee Valley Authority, and Electric Power Research Institute initiated a field study in 1994 to address the feasibility of LSS and FA co-utilization for mine spoil reclamation. To complement the field study, simulated laboratory weathering of unamended and amended mine spoil was initiated to assess the potential long-term influence of LSS and FA on mine spoil systems.

The total elemental content of the FA, LSS, and mine spoil was determined by employing both HNO3 extraction and total digestion (aqua regia/HF). The percent recovery of elements by HNO3 digestion was determined by dividing the HNO3-extractable concentrations by the total elemental content determined using the aqua regia/HF method. Variations in HNO3-extractability of metals in the mine spoil, LSS, and FA was a function of element speciation in the mineral phase. In general, HNO3 digestion was more efficient at extracting Al, Ca, Mg, Cr, Cu, Pb, and Zn from LSS; K and Na from the FA; and Fe, Mg, P, Co, and Mn from mine spoil. Further, HNO3-extractability was not a function of total concentrations and the HNO3 digestion method did not yield a constant percent extractability that could be uniformly applied, irrespective of material.

The chemical analyses of amended mine spoil leachates showed a neutralization of acidity generated by pyrite oxidation. Slight pH and nitrate fluctuations were observed during the later weathering cycles, which may have been due to increased microbial activity. Also, the initially high electrical conductivity (EC) of the mine spoil leachates was increased further upon LSS application and did not vary with FA rate. The EC of all mine spoil leachates decreased with weathering and mirrored the behavior of Ca and SO4. The dissolution and mobilization of Al, Fe, K, Cu, Mn, Ni, and Zn decreased upon LSS application, irrespective of FA rate.

A sequential-selective dissolution (SSD) procedure partitioned elements (Ba, Co, Cr, Cu, Mn, Ni, Pb, Sr, and Zn) into the following operationally-defined pools: (1) soluble-exchangeable, (2) adsorbed, (3) organic, (4) carbonate, (5) sulfide, and (6)residual. The speciation of Ba increased in the soluble-exchangeable and carbonate fractions with increasing FA rate. Strontium increased in the soluble-exchangeable and sulfide fractions with increasing FA rate. Weathering tended to shift Ba to the carbonate fraction and Sr showed no significant shifts to any other phase. Chromium found in the residual fraction significantly increased upon LSS application. Weathering of the LSS-amended mine spoil increased Cr found in the adsorbed fraction, yet maintained predominance in the residual fraction. Chromium solid-phase speciation was not impacted by FA application or weathering. Although primarily found in the residual fraction, Co showed a significant decrease in the soluble-exchangeable form upon LSS and FA application in the weathered material. In general, FA did not impact Co solid-phase speciation. However, LSS application decreased Co found in the soluble-exchangeable fraction. Copper speciation decreased in the soluble-exchangeable and residual fractions upon LSS application with an increase in the carbonate fraction. Primarily, weathering shifted Cu into the residual forms. Fly ash rate had no influence on Cu speciation for the weathered or unweathered mine spoil. In general, increasing FA rate increased Ni found in the residual fraction. Weathering shifted Ni into the carbonate and sulfide forms which decreased with FA application rate. However, Mn was primarily found in the soluble-exchangeable and residual fractions, irrespective of amendment. Weathering shifted Mn into the carbonate form in the amended mine spoil upon LSS application and into the residual form for the unamended mine spoil. Upon LSS application, Pb decreased in the soluble-exchangeable fraction. However, when weathered, amendment did not influence Pb solid-phase speciation. In general, FA rate increased the carbonate form of Zn in the unweathered material. However, weathering shifted Zn from the soluble-exchangeable and sulfide forms into the carbonate fraction, which was influenced by the LSS. In general, the impact of FA co-application with LSS was element specific with respect to the solid-phase speciation of elements.

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