Abstract
The Canadian Nuclear Laboratories (CNL) is developing a long-term management strategy for its existing inventory of solid radioactive cemented wastes, which contain uranium, mercury, fission products, and a number of minor elements. The composition of the cemented radioactive waste poses significant impediments to the extraction and recovery of uranium using conventional technology. The goal of this research was to develop an innovative method for uranium, mercury and cesium recovery from surrogate radioactive cemented waste (SRCW). Leaching using sulfuric acid and saline media significantly improves the solubilization of the key elements from the SRCW. Increasing the NaCl concentration from 0.5 to 4 M increases the mercury solubilization from 82% to 96%. The sodium chloride forms a soluble mercury complex when mercury is present as HgO or metallic mercury but not with HgS that is found in 60 °C cured SRCW. Several leaching experiments were done using a sulfuric acid solution with KI to leach SRCW cured at 60 °C and/or aged for 30 months. Solubilization yields are above 97% for Cs and 98% for U and Hg. Leaching using sulfuric acid and KI improves the solubilization of Hg by oxidation of Hg0, as well as HgS, and form a mercury tetraiodide complex. Hg and Cs were selectively removed from the leachate prior to uranium recovery. It was found that U recovery from sulfuric leachate in iodide media using the resin Lewatit TP260 is very efficient. Considering these results, a process including effluent recirculation was applied. Improvements of solubilization due to the recycling of chemical reagents were observed during effluent recirculation.
Highlights
Canadian Nuclear Laboratories (CNL) is developing a long-term management strategy for an inventory of cemented radioactive waste, which contains uranium, mercury, fission products, and a number of minor elements
Best results were obtained using a sulfuric acid leaching in saline it has as been successfully for the chemical leaching of antimony acid leaching in media saline as media it applied has been applied successfully for the chemical leachingand of other metals from small armsfrom shooting
Results show that part of the mercury occurs as mercury oxide but part of this mercury oxide has been reduced to metallic mercury and some has Several surrogate radioactive cemented waste (SRCW) were cured at 60 ̋ C and several were aged for 30 months
Summary
Canadian Nuclear Laboratories (CNL) is developing a long-term management strategy for an inventory of cemented radioactive waste, which contains uranium, mercury, fission products, and a number of minor elements. An earlier study indicated that extracting the uranium would be advantageous for decreasing the radioactivity of the waste and, reducing the hazards and cost of long-term management [1]. There are safety and economic incentives for the extraction of uranium, mercury and cesium before subjecting the cemented waste to a stabilization process. The cemented waste differs significantly from common uranium ores, mostly hosted in quartz or granite with typically more than 40% silica. The composition of the cemented radioactive waste poses significant impediments to the extraction and recovery of uranium using conventional technology
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