The retardation of technetium by an antimony-containing mineral, stibnite, and of iodine by a mercury-containing mineral, tiemannite, has been studied using column experiments. Data are presented and possible retardation mechanisms are discussed.The addition of as little as 10% of stibnite to a column of crushed granite was found to be sufficient to retard the transport of technetium through the column. The effect of flow rate on the retardation of technetium was considerable: at a linear velocity of 3 cm/h, about 30% of the injected technetium was eluted from a column of pure stibnite without retardation; at a velocity of 0.43 cm/h, all technetium was retained by the column. Examination of the column after the experiment gave a retardation factor of 500-650. This retardation is thought to be due to the reduction of Tc0 4 " to Tc(IV), rather than an ion exchange mechanism.Iodide was found to be strongly sorbed to tiemannite, with only 10% eluted without retardation. This retardation of iodide is possibly due to the formation of an insoluble iodide species.
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