The net result of mining is ore containing the uranium. Like any other ore, it has to be processed to make it into a usable product. The next step is called milling. The uranium ore is hauled to a milling plant, where it is crushed into finer particles before being leached with sulfuric acid or alkaline solutions to dissolve the uranium from the ore. The leaching solution also extracts other heavy metals, such as vanadium, molybdenum, selenium, iron, lead, and arsenic, along with the uranium. The slurry is washed and clarified before heading to a solvent extraction area, where the uranium is removed from the solution by ion exchange columns. After another aqueous phase, a yellow slurry of uranium oxide (U3O8) is produced that is dried to make the final product—yellowcake— which is packed in 55-gallon steel drums and is ready for further processing to make uranium fuel pellets (12). The waste products from the milling plant include the fine-grained solids remaining after extracting the uranium and liq­uids from the slurry. These go into a mill tailings holding pond that contains toxic heavy metals that occur in the ore, as well as radium and radon, which are always associated with uranium. The radiation and heavy metals in mill tail­ings have to be carefully monitored and controlled under regulation by the US Nuclear Regulatory Commission (NRC) (13).

It hasn’t always been that way. Numerous mill tailing sites, left over from the mining binge of the 1950s to 1980s, were left in place, causing environmental problems. One particularly notorious site was the Climax uranium mill in Mesa County near Grand Junction, Colorado. The Climax Uranium Company let pub­lic and commercial interests have access to the mill tailings to be used as fill mate­rial and in concrete and mortar in housing construction. This led to excessive levels of radium and radon in more than 4,000 private and commercial properties in and around Grand Junction (14). The only scientific study that has been done to determine whether radiation from the mill tailings in houses and commercial buildings in Mesa County caused cancer was negative, however. Although leuke­mia rates from 1970-1976 were twofold higher in Mesa County than in Colorado overall, there was no excess incidence of lung cancer. Furthermore, the leukemia cases were unrelated to any excess exposure to radiation from mill tailings (15).

Congress passed the Uranium Mill Tailings Radiation Control Act in 1978 that authorized the US Department of Energy (DOE) under the Uranium Mill Tailings Remedial Action Project to clean up inactive uranium milling sites, including the one at Grand Junction. Houses and businesses with high levels of radiation were either demolished and the radioactive materials hauled away to a proper disposal site or were remediated (14). A milling site at Shiprock in the Navajo Nation was also contaminated and is still undergoing remediation (16). Overall, 22 mill tail­ings sites have been cleaned up by the DOE.

It is worth asking whether the radiation emanating from these milling sites actually caused higher rates of cancer in the general population around them. The answer is no, with the exception of an increased risk of lung cancer for those men who actually worked in underground mines. Montrose County, Colorado, had more uranium mines and mills than anywhere else in Colorado—a total of 223 mines—but a 50-year study of people living in Montrose County found that they had the same mortality rate as the general Colorado population. The only exception was a nearly 20% increase in lung cancer among men, most likely due to working in underground mines and smoking (17). Another epidemiological study of people living in Uravan—a town in Montrose County named by combin­ing uranium and vanadium—found that the overall rate of mortality was 10% less than the national average, and the average mortality from all cancers was equal to the national average. Again, the sole exception was an enhanced risk of lung cancer. The lung cancer mortality rate among underground miners was double the national average, but it was not elevated among Uravan residents who did not work in mines (18).

The history of cavalier attitudes about uranium mining and milling and lack of regulation has ended. As a sign of the future, the first new uranium mill since the Cold War was recently approved in the Paradox Valley in Montrose County near Naturita, Colorado, about 50 miles south of Grand Junction, though not without controversy (19, 20). Naturita is the site of a legacy uranium mill that has been cleaned up by the DOE, but the new mill would be under strict regulatory control and should prove that milling sites can be operated with minimal environmental damage.