Investigating the Relationship Between Fouling Metal Precipitation, REE Concentration, and pH in Acid Mine Drainage
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Date
2024-12
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The Ohio State University
Abstract
Acid mine drainage (AMD) is a hazardous byproduct of coal and ore mines. It occurs when a mine is exposed to ground or surface water and iron sulfide within the mine dissolves in the water and reacts with the oxygen dissolved in the water. The result is a highly acidic solution which can leach metals from exposed minerals into solution. This study investigated pH and age-driven precipitation of metal cations and rare earth elements (REEs) in a model Ohio AMD. REEs have become a staple resource for production of technology used in healthcare to transportation (Rare Earth Elements, n.d.). There are ways to source them from AMD, but several hurdles must be overcome for that to become feasible. One hurdle being the presence of fouling metals, which co-precipitate with the REEs and interfere with isolations processes. The primary metal cations in solution were aluminum, iron, and manganese, the REE used was yttrium. Several titrations were conducted to determine an optimal pH range and oxidation level to hold REEs in solution and an evaluation of age was done to monitor the stability of the solutions over time. Determining the conditions which allow for the highest pH adjustment with the most REEs kept in the AMD opens a window to effective sorbent use where there wasn’t one before. The pH of an AMD solution was titrated using a sodium hydroxide solution and evaluated for fouling metal (Fe, Al and Mn) and REE concentration (Y). Another portion of AMD was left to age and its components were evaluated several times a week for 4 months. The AMD solution was also modeled in Visual minteq to provide a basis for expected behavior of elements. These results will demonstrate a pH adjustment that results in Al, Fe, and Mn precipitation without the loss of REEs.
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Keywords
Acid Mine Drainage, Rare Earth Elements, pH Adjustment, Precipitation of Metal Cations