Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Louis M McDonald
Acid mine drainage (AMD) is an environmental concern that is well known and studied in West Virginia and other mining regions. This pollution threat can be prevented and mitigated with current mining permitting regulations; however some mine waters require treatment, which generally consists of the neutralization of affected waters, resulting in the precipitation of characteristic 'floc' material. AMD floc consists of hydroxides of heavy metals; predominantly iron. This study simulated AMD treatment practices to evaluate the effects of common environmental controls; namely the presence of organic matter (OM) on the formation and settling behavior of Fe hydroxides with the ultimate goal of the optimization of active AMD treatment. Hydroxides were synthesized through the forced hydrolysis of mixed FeCl3 and organic acid solutions. Organic acids varying in number of carboxylic functional groups to include acetate (a monodentate ligand), malate (a bidentate ligand), and citrate (a polydentate ligand) were used as analogs for OM in surface water. It was hypothesized that the addition of organic acids to the Fe system would promote complexation, and as a result produce fewer iron hydroxides. Hydroxide mass, volume, percent of amorphous hydroxide, compression rate, and soluble iron concentrations throughout the titration were measured. The presence of organic acids led to decreased hydroxide mass, increased hydroxide volume, and less pronounced compression after settling. The solubility experiments showed that OM in solution allowed precipitation at lower than expected pH values, and allowed for redissolution of Fe at high pH, suggesting that OM hinders hydroxide crystallization.
Mannix, Marianne A., "The Effect of Organic Acids on the Formation and Behavior of Synthesized Iron Hydroxides: Implications for Acid Mine Drainage Treatment" (2015). Graduate Theses, Dissertations, and Problem Reports. 6157.