Semester

Fall

Date of Graduation

2005

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Roger C. Viadero, Jr.

Abstract

Acid mine drainage (AMD) is one of the significant environmental challenges for the coal and hard-rock mining industry. Traditional AMD treatment generates large volumes of sludge with low solids which are difficult to dewater. In this study, a systematic investigation was carried out on the characteristics and dewaterability of AMD sludge produced from an ammonia neutralization operation, and the dewatering performance of different treatment options. In order to mitigate the AMD sludge problem, a selective precipitation process was developed to recover Fe and Al while AMD was treated simultaneously. In conjunction, a low-cost synthesis approach was examined to prepare magnetite nanoparticles with the recovered iron from AMD, and its implication in environmental engineering was discussed.;The AMD sludge from ammonia neutralization was characterized by high pH and alkalinity, high total Fe and Al, elevated sulfate, and low solids (0.72 +/- 0.24%). Compared to other AMD sludges and metal hydroxide sludges, ammonia-treated AMD sludge demonstrated relatively good dewaterability in terms of specific resistance to filtration. Coagulation and flocculation treatment did not effectively reduce the final volume of the settled sludge. Sludge cakes with 6.2% solids and a filter yield of 3.04 kg/m2h were achieved by vacuum filtration. Additionally, a belt filter press showed a good performance in improving solids content of the sludge cake.;Simultaneous metal recovery and AMD treatment were achieved using a selective precipitation process based on solubility characteristics of the major and minor metals in the AMD. Separate iron and aluminum hydroxide products with relatively high purity were successfully recovered via iron precipitation at pH 3.5-4.0 followed by aluminum precipitation at pH 6.0-7.0, while simultaneously meeting the NPDES effluent discharge standards. The proposed metal recovery process was relatively easy to implement in the field.;An approach to synthesize low-cost magnetite nanoparticles via coprecipitation was developed with the recovered ferric iron from AMD as the iron source. Through scanning and transmission electron microscopic studies, it was demonstrated that most of the magnetite nanoparticles ranged from 10 to 15 nm and were spheroidical or cubic in shape. Consequently, the recovered ferric iron from AMD could be used as a low-cost substitute feedstock for reagent-grade chemical for magnetite nanoparticle preparation, which provided great opportunity for the application of magnetite nanoparticles in environmental engineering.

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