Effect of aluminum oxyhydroxide coatings on the performance of limestone drains

Neutralization by limestone is a common treatment for acid mine drainage (AMD). The effectiveness of using limestone to treat AMD can be reduced by aluminum (Al) and iron (Fe) oxyhydroxide coatings that form on the limestone, because the coatings inhibit the transport, and thus neutralization, of hydrogen ions (H+) derived from acid mine drainage. I used mixed flow reactor experiments to investigate the effect of Al coatings on the diffusion of H+ to the surface of limestone and to quantify how those Al coatings affect the limestone dissolution rate. Experiments used acidic Al sulfate solutions with initial Al concentrations ranging from 0.002 M to 0.01 M (32 to 329 ppm) and pH values ranging from 3.7 to 4.2, which are typical of conditions found at AMD sites. Cleaved pieces of Iceland spar calcite were used as a proxy for limestone. The pH was measured in the effluent to determine the rate of H+ consumption. Effluent solutions were analyzed for Al, calcium (Ca) and sulfur (S) using inductively coupled plasma optical emission spectroscopy (ICP OES). Examination of the precipitated coatings using x-ray diffraction indicated that amorphous poorly crystalline gibbsite is the primary Al coating but scanning electron microscope analysis also suggests the possible presence of a poorly crystalline sulfur containing phase, such as hydrobasaluminite. The experimental data were used to calculate the diffusion coefficient of H+ through the Al coatings. The calculated diffusion coefficient for H+, assuming a gibbsite and/or hydrobasaluminite layer, ranged between 10-13 to 10-11 m2/sec, that are significantly lower than in pure water.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Geosciences

Department dc:contributor.department

Geosciences

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2018

Author dc:creator

• Palomino Ore, Sheyla Bethsy

Chair dc:contributor.committeechair

• Schreiber, Madeline E.

Committee members dc:contributor.committeemember

• Rimstidt, J. Donald
• Seal, Robert Rhodes
• Chermak, John Alan

• Acid mine drainage
• limestone drains
• aluminum
• oxyhydroxide
• coatings

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

vt_gsexam:14768

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/83860