LEACH TESTING OF MINE WASTES: ENVIRONMENTAL IMPACT AND METAL MOBILITY IN WATER SUPPLIES AND BODY FLUIDS

The mining industry has generated hazardous wastes containing contaminants that pose a threat to human health such as As, Cu, Hg, and Zn. However, the bioavailability of these metal(loid)s is often complicated to assess or compare due to variable geo- and biochemical conditions under which they may be extracted from mine wastes. In addition, particle size of the mine wastes can influence metal concentration trends and reactivity in ways that have not been thoroughly explored. Extractions of metals from mine wastes with water and simulated lung and gastric fluids were conducted to simulate the exposure of size-separated mine waste fractions to these extractants and predict the amounts of metals likely to become mobilized, hypothesizing that the amount of metal released would increase with the amount initially present and with decreasing particle size.

Samples were separated into 11 particle sizes ranging from >2830 um to <20 um. Selected size fractions from two Kelly Mine and two Hocker Flat samples were placed into separate test tubes with DI water adjusted to pH 5.5 using a 4:1 liquid-solid ratio. Solutions were rotated for 18 hours at room temperature, centrifuged, filtered to 0.45 um, and acidified to pH < 2. Concentrations of As, Hg, Cu, and Zn in solution were then determined through atomic absorption analysis.

In the Kelly Mine samples, no As or Hg were released into water, suggesting they were present as insoluble forms. Mobilized amounts of Cu and Zn generally followed the trends of their initial concentrations in the sample. However, despite increasing initial concentrations in the Kelly Mine samples, levels of released Cu and Zn leveled off, suggesting that speciation is important in the leachability of metals from different particle size fractions.

In the Hocker Flat samples, only Zn was detectable, and in very small amounts, despite significantly higher initial concentrations than the Kelly Mine samples. This lower solubility is probably due to the greater degree of transport experienced by the Hocker Flat samples, signifying greater weathering and removal of more soluble phases.

Additionally, simulated lung and gastric fluid extractions were conducted to study the threat of inhaled and ingested metal-containing particles from mine wastes, and these results were compared to those of the water extractions.