In December 2011, Marenica Energy determined that the Marenica uranium project in Namibia, with a Mineral Resource estimate of 276 Mt at a head grade of 94 ppm U3O8 was sub-economic at current and projected uranium prices using conventional processing methods of heap or tank leaching and for the project to be viable an upgrade of the uranium prior to leaching was required.
In February 2012, a test work program commenced attempting to determine if ore could be economically upgraded prior to leaching. The goal was to reduce the tonnage to be processed by the leach circuit, being a significant cost for any uranium project. The program was split into two phases:
■ Phase 1 – scoping level bench top test work on samples existing in Perth to determine the uranium mineralisation and potential upgrading. Mineralogical test work concluded that the uranium mineralisation has distinctive characteristics. It occurs as a single mineral, in a distinct size band, is well liberated and is heavier than the surrounding rock. These characteristics present an opportunity to apply well established physical processes to upgrade the uranium. Phase 1 is complete and the positive outcomes were the basis of moving to Phase 2.
■ Phase 2 – involved the extraction of representative bulk samples to feed an extensive test work program to evaluate the upgrade potential using well-established and comparatively low cost processes that are scalable to large tonnage operations. Phase 2 has now been completed. The next phase of testing is flowsheet development, which includes optimisation of the flowsheet as well as optimisation of the concentrate upgrade ratio and maximising the uranium recovery to concentrate. Marenica is also testing the variability within the resource. The upgrade occurs in two stages, a primary and secondary upgrade. Primary upgrade test work has produced upgrade ratios of between 3 and 4 and the secondary upgrade produced a grade increase of 15 to 25 times. The total upgrade ratio of the primary and secondary upgrade stages is therefore >60 times at a recovery >65%, which is above Marenica’s expectations.
The upgrade process has been very successful and has reduced the leach feed to about 1% of the beneficiation plant feed due to significant rejection of the major gangue mineral of calcite. This successful calcite rejection has also enabled the proposed leach circuit to be changed from an alkali leach (with higher operating temperatures and slower kinetics) to an acid leach (at ambient temperature and rapid kinetics), reducing expected capital and operating costs. The leach feed is therefore expected to be only 200,000 t/y from 20 Mt/y mined, and the leach feed grade is expected to be >5,500 ppm U3O8.
The rejection of 99% of the mass using low cost mechanical processes is also expected to result in a relatively benign environmental impact, with only 200,000 t/y expected to be leached.
The company continues to work on optimizing the beneficiation flowsheet to concentrate the uranium, an approach it believes is unique in the uranium industry and over which the company has filed a provisional patent application.
By rejecting 99% of the original mass prior to the leaching circuit, the estimated capital and operating costs are significantly lower than those which would typically be expected to process the ore, thereby significantly enhancing the potential project’s economics.