Research Of Releasing Mechanisms Of Contaminants From Uranium Tailings By Heap Leaching

Uranium mill tailings represent a high volume of low specific activity radioactive waste. As the uranium tailings are usually disposed on surface as impoundments, radionuclides and other hazardous materials may be leached from the tailings due to geochemical process, polluting water and soil around the impoundments,which is harmful to human beings. Research on the releasing behavior and mechanisms of contaminants from tailings is helpful to formulate corresponding measures to decrease the adverse environmental impacts of uranium tailings. Guangdong and Jiangxi Province, which is humid, in China are riched in uranium ore, there are, however, few reports about the leaching and migration mechanisms of radionuclides and toxic metals from these uranium tailings. Therefore, it is significant to conduct research on these uranium tailings.In this paper, the uranium tailing collected from a uranium impoundment in Shaoguan, Guangdong Province, is the research object. Analyses on physical and chemical properties of the tailing was done. A dynamic leaching test simulating natural conditions was carried out to study the release behaviors of uranium(U) and other contaminants in the tailing. Then the kinetics of these contaminants were analyzed. The conclusions are as follows:1. The uranium tailing partical size mainly ranges from 0.1~10mm. It mainly consists of silicon, iron, aluminum, and potassium. The main minerals in the tailing are quartz, muscovite, microcline, kaolinite gypsum and clinochlore. Most of uranium, lead, zinc and cadmium exist in residue species, however, iron and manganese exist mainly in Fe-Mn oxides/hydroxides combinding species.2. p H of the leachates from dynamic leaching test ranges from 3.3~4.84, increasing with time. And the release of contaminants in the tailing, such as U, Fe, Mn, Zn, Cd, Pb and SO42-, are fast in the initial stage and then became slow. The concentration of U in the leachate is much higher than the emission limit 50 ug/L for uranium tailings, concentration of other contaminants also exceed the values confined by quality standard for ground water, China.3. The accumulative leaching amount of metals in the decreasing order is of U>Mn>Fe>Zn>Cd>Pb, which is determined by the total content of element and its occurrence forms.4. The maximum concentration of U in the leachate is 286.66 mg/L, and the accumulative amount of U is 158.06 mg/Kg by leaching 2 months.5. The kinetics of Fe, Mn could be properly described by second order kinetic equation, however, that of Pb, Zn, Cd could be properly described by parabolic diffusion equation. For U, the kinetics of it could be perfectly described by first order kinetics equation during 0~24 h, but by second order kinetic equation during 24~1464 h.