Rates of leaching of radium from contaminated soils: An experimental investigation of radium bearing soils from Port Hope, Ontario

Abstract

The leachability of Ra-226 from soil at Port Hope, Ontario contaminated by waste from a long established U refinery is described here. A small-scale static leach test was devised to provide information to permit an assessment of hazard due to leaching in the environment. Two different leaching solutions were prepared to simulate a range of infiltrating water quality in disposal environments: one by bubbling Cot into distilled water to pH 5.5, and another by bubbling SO₂ into water to pH 3.5. Narrow-range size fractions of the soils (i.e. 0.250 to 0.105 mm) were leached for 30 to 45 days (equivalent rainfall of 2 to 3 yr). It was found that leaching is significantly affected by soil texture, total amounts leached and the maximum concentrations reached being much greater for coarser and intermediate size fractions than for fine soil fractions. Also, leachant acidity significantly increased leaching rates and resulted in enhanced mobility in soils. A straight line for the plot of Q/Q ₀ (cumulative fraction released) vs. $T^{{\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 2$}}}$ (T is leaching time in days) indicated that leaching could be considered to be a diffusion phenomenon in accordance with Fick's law. Diffusion coefficients ranging from 5 × 10⁻¹¹ to 2 × 10⁻¹³ cm² day⁻¹ were found. These coefficients provide a basis for estimating the fraction that would be leached over longer periods.