New Mexico Geological Society Annual Spring Meeting — Abstracts

Exposure to trace metals (As, U, Cr, Cu, Pb, Zn) have potential negative health effects on human populations and wildlife that are exposed. Geothermal waters often have elevated concentrations of trace metals and understanding their geochemical cycling can be challenging. Previous studies have utilized in situ stream pebbles and glass or ceramic substrates to examine the association of trace metals with iron-manganese oxide coatings to understand contamination and chemical cycling. This project’s main focus is to develop an extractive method using adsorption onto substrate surfaces in both natural and engineered environments and to characterize the phenomenon of adsorption/coprecipitation between trace metals and these surface coatings. Sampling locations include the Jemez River and Rio San Antonio in northern New Mexico, which have significant geothermal inputs from the Valles Caldera system. Factors such as leachate type, water pH, substrate type, coating accumulation period and leach time were all considered in this experiment. It was found that of the three leachates: aqua regia, 10% aqua regia and hydroxylamine at pH 2, hydroxylamine at pH 2 was the most effective at leaching coatings without dissolving substrates. Samples leached with aqua regia and 10% aqua regia were found to have had a significant weight gain post leaching and then weight and mass loss occurred over the following 5, 7, and 10 day measurements. Glass beads were determined to be more effective than in stream pebbles as accumulation data was more easily controlled and monitored. Substrate samples leached with hydroxylamine for 5, 24, 48 and 72 hour intervals showed little difference in their leachate concentrations, suggesting that leach time has little impact on the concentration of leachate samples. Adsorption rates of metals of copper, lead and zinc had similar values over 3, 5 and 7 week intervals in the Jemez system. Batch experiments to determine trace metal capacity on iron-manganese oxides are in progress. This research aims to find the best method for determining trace metal loading to aid in understanding geochemical cycling.