The wastes produced during the milling process and stored in tailings impoundments are the principal source of milling-related health and environmental hazards. Typical properties of these mill tailings are shown in Table AIV-1. During the milling process, nearly 90% of the uranium contained in the ore is removed, and so the primary radiological concern is the remaining progeny associated with uranium such as thorium, radium, radon, and lead. The actual activity of these uranium progeny can vary depending on the specific methods employed,; however, as much as 50-86% of the original activity of the ore is retained in the mill tailings (U.S. EPA 2006). Hazardous stable elements are also extracted from the ore and transferred to the tailings piles, including arsenic, copper, selenium, vanadium, molybdenum, and other trace heavy metals.
AIV-The five on-site environmental pathways through which these tailings impoundments pose a risk are represented schematically in Figure AVI-3. In addition to the on-site scenarios, tailings have also been taken off-site and used as an inexpensive building material by some local populations. Each of these hazard pathways is listed below and the associated risks are discussed later.
(i)
The release of gaseous radon-222 to the atmosphere and subsequent inhalation
(ii)
Possible dust loading of contaminants from the impoundment due to natural wind conditions
(iii)
The localized effect of direct external gamma radiation exposure from the tailings impoundment
(iv)
Ground seepage and subsequent contamination of local aquifers, which has the potential to affect the water supply
(v)
Dam failure due to erosion or natural disasters (flood, earthquake, etc.)
(vi)
Improper use of tailings as a building material
All six of these hazard scenarios can apply to the general public and, with the exception of building materials, to the plant workers themselves. In addition, plant workers have added risks associated with accidents that may occur within the mill.
Read more:
http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-volii/402-r-08-005-v2-appiv.pdf
