SurfMin: Mine Pits

NTIS Accession No: NTIS List Price:

Title of Report:

DIAGENESIS AND LEACHING CHARACTERISTICS OF AGED COAL CONVERSION SOLID RESIDUES

FROM MINE DISPOSAL ENVIRONMENTS (June 1995) 26pp.

Performing Organization Name and Address:

Energy & Environmental Research Center

University of North Dakota

Grand Forks, ND 58202-9018

Type of Report: Mining research contract report

Abstract:

Disposal in mine pits is the current fate of most combustion ash. Prediction of

long-term impact should rely on field monitoring and performance, but lack of

field data often puts too much reliance on laboratory testing to simulate

performance. This study provides test results for cores extracted from several

engineered disposal cells in western North Dakota dating to 1983 and containing

scrubber ash and bottom ash produced by a conventional combustor.

The mineral transformations and diagenesis have been spectacular and varied.

Early reactions with water transformed basic reactive mineral phases in raw

material to various cemetitious and hydrated phases. (Once completed and

capped, the cells have minimized contact with air and water.) Significant

amounts of ettringite, thaumasite, tobermorite, and some Na-Pl zeolite,

sodium-calcium sulfate, calcite, and gypsum were identified. Some cores

contained 70% thaumasite or tobermorite.

Synthetic groundwater leaching procedure (SGLP) leachates had pH 10-11 and

composition of sodium and sulfate, with little ease. Resource Conservation and

Recovery Act (RCRA) and other important metals in the ash cores did not leach.

Core tests indicated unconfirmed compressive strengths ranging from 208 to 5075

psi, permeability 1.7 E-4 to 2.1 E-6 cm/s, bulk density 70 to 100 pcf, and

moisture 16% to 38%. Groundwater was not involved in the performance of these

disposal cells.

In addition to direct impact in current disposal cell construction, operation,

and monitoring practices, these results can guide ash use in underground mine

stabilization projects.

Keyword(s):

Mine pits

Scrubber and bottom combustion ash

Leaching measurements

Underground stabilization

Author(s)

Ray D.Butler and Debra F.Pflughoeft-Hassett