Xenia De Gracia Medina

Mentor:

Dr. Jon Chorover

Department: 

Environmental Science

Abstract: 

Characterization of mine tailings from legacy mine sites in Montana, Nevada, and Arizona.

Many legacy mines have tailings that have been exposed for hundreds of years to the climate conditions of each site. They contain different minerals and metal(loid)s that can enhance or limit the transport of hazardous elements into the subsurface or transported as airborne particulate matter. These weathering processes can affect the health of the surrounding environment and population. To elucidate the possible hazards, it is essential to characterize these residues' physical and chemical properties by different techniques. Mine tailings from polymetallic sulfide ore from three States in the Western US were characterized: a humid climate in Montana (Keating and Mammoth), a dry climate in Nevada (Tybo), and a moderate climate in Arizona (Iron King). Elemental composition was screened on-site using a portable X-ray fluorescence (PXRF). The specific surface area (SSA) of the tailings was analyzed through the BET N_2(g) absorption technique, using Micromeritics Gemini VII to obtain information on tailings surfaces available for reaction and metal(loid)s adsorption. Particle size distribution (PSD) was studied using LS 13-320 laser diffraction particle size analyzer. Knowing the distribution of particle sizes helps to understand the material’s potential porosity and reactivity. X-ray diffraction was used to analyze the mineralogical composition of the tailings. Batch and flow-through experiments were conducted to monitor the developed pH changes and released metal(loid)s in tailings exposed to water and oxygen. Tybo, NV, tailings have the highest concentrations of toxic metal(loid)s studied. Pb was higher at the surface compared to deeper areas (~1 m). At Mammoth in MT, Pb was lowest at the surface and the highest at deeper layers. Based on the calcium concentration of the three sites, Tybo has the highest acid neutralization capacity. This can be seen in the flow-through reactive experiment, where it maintains its neutral pH. From the batch and flow-through reactive experiments, Mammoth becomes acidic faster than the other sites. Mammoth has the highest specific surface area and the smallest particle size of the three sites, meaning it can have the highest reactivity. The tailings from varying climates show weathering depth profiles and products, as well as metal(loid) release, that differs by site.