The mining and production of uranium in the Czech Republic has left a significant environmental legacy. Besides waste heaps, sludge settling lagoons etc, which remained after the underground mining activities, the consequences of underground, uranium in-situ leaching, represent a special problem.

In the North-Bohemian area, the state organization DIAMO operated one in-situ leaching plant at Straz pod Ralskem. Previously approximately 4 million tons of sulfuric acid were pumped underground. The necessary site remediation activities, which are being financed by the government, are based on groundwater pumping, followed by a technological process which recovers some dissolved components (uranium, alum etc.) and ensures the decontamination of the remnant solution.

This paper deals with the possible development of a process, designed to remove thorium nuclides and another process, which will ensure the safe disposal of the remnant solution, containing the bulk of the radionuclides.

Thorium radioisotopes represent the major part of the groundwater radioactivity and their removal by sorption could simplify the successive process steps. Special sorbents (ion exchangers) have been proposed and prepared. The sorbent preparation was based on sawdust phosphorylation. The resulting sorbent was highly selective for thorium and provided a reasonably economic process of recovery leading to a product suitable for disposal.

The technology proposed for the groundwater treatment will result in high volumes of remnant solutions containing the majority of the radioactive elements. To ensure the safe disposal of this material into the existing tailing ponds, a special solidification process was studied. It was based on the evaporation and calcination of the remnant solution. This process resulted in a considerable volume reduction of the initial solution. The quality of the final calcination product was improved by selected additives, which stabilized the most dangerous radiotoxic elements — radium and thorium.

The results of both processes described will be evaluated for their economic viability and feasibility in the context of solving the overall problem.

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