New Mexico Geological Society Annual Spring Meeting — Abstracts

Rare earth elements (REE) are of economic importance today because of modern-day technologies, including magnets, electrical components, and industrial components needed for national defense. Humates are organic compounds containing humus, which is known to be available in soil and coal byproducts. These products are abundant, low-cost, and are sold commercially for use in several products, including nutrients for soil for better plant growth, cosmetics, filtration, and other uses. Although the concentrations of REE are relatively low in coal and humates (<600 ppm total REE), the volumes of coal and humate produced is large and makes them an attractive source for potential by-product REE production. The Menefee mine in northern New Mexico processes humates with average concentrations of total REE (TREE) from 113-179 ppm. In this study, five humate samples from two different mines were analyzed using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) to quantify REE. The metals were extracted using two methods, RO (reverse osmosis) extraction and acid digestion (via microwave). Before extraction, samples were prepared by oven drying the samples, grinding them using mortar and pestle and then sieving them through a 45-micron sieve. During RO extraction, the samples were mixed one-part humate to five parts RO water, shaken continuously for an hour, then centrifuged. One sample was shaken for a total of 72 hours to compare TREE extracted to shaking for one hour. The samples were filtered with Whatman funnel filters before analysis. Before acid digestion, samples were split into smaller aliquots (about 0.25 gram) using a riffler splitter. The acid digestion was conducted using 5 mL nitric acid and 2 mL hydrofluoric acid, and samples were filtered with Whatman funnel filters and diluted to about 1% acid before analysis. The solutions from the two methods of extraction were then analyzed by ICP-MS at the New Mexico Bureau of Geology and Mineral Resources Analytical Laboratory. The TREE concentrations were generally low for these samples. A high ratio of LREE (light rare earth element) to HREE (heavy rare earth element) was observed. A longer shaking step resulted in higher TREE concentrations. An elevated concentration of TREE was also present in a white filtrate produced after the hydrofluoric acid step in the microwave digestion.