TUC Resources Limited (ASX:TUC) is very pleased to report recoveries of up to 85% from the latest leach tests on Heavy Rare Earth (HREE**) rich clays from the Stromberg Prospect. This is a 10% improvement on initial test work.
Two composite samples have been tested using a multi-stage leach process involving initial caustic wash followed by acid leach at a range of concentrations. Up to 85% TREE recovery was achieved using leaching by sulphuric acid (one part acid to two parts water) after an initial caustic wash using sodium hydroxide.
Promisingly, work indicates that recovery from lower grade material is comparable to higher grade, with a 0.2% to 0.4% Total Rare Earth (TREO*) composite giving an 77% recovery of TREE. It appears from work that the caustic wash improves the amenability of the mineralised material to the leach process.
Leaching of the HREE directly into solution can result in a more direct processing route to an HREE intermediate/carbonate material, which would allow TUC to generate more competitively valued product, when compared to other concentration methods.
The leach tests also extracted up to 93% of uranium mineralisation, possibly creating a secondary revenue stream for the project, whilst simultaneously serving to boost marketability and exportability of any future HREE product.
Furthermore, all of the deleterious element Thorium was left behind in the residues, significantly upgrading the quality/marketability of any final product.
It should be noted, that although these results are impressive, test work is still at an early stage. To date 70% recovery of yttrium has been achieved with a respectable acid consumption of 371kg/t. Efforts are now being made to improve the efficiency of the process including; reducing reagent consumption by testing variation in leach times, acid to mineralised material mixes, and leach temperature.
*Total Rare Earth Oxides (TREO's) have been calculated by addition of common oxide values for Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Tm, Yb, Y. REO values have been calculated from rare earth element (REE) ppm grades after analysis by lithium-metaborate fusion and ICPMS , where possible, or by HF/multi acid digest and ICPMS. The total REO is calculated as the sum of all REE as REE2O3, with the exception of Ce, Pr and Tb; which are calculated as CeO2, Pr6O11, and Tb4O7 respectively, in accordance with geochemical conventions.
**Heavy Rare Earth Elements HREE's = Dy, Er, Ho, Lu, Tb, Tm, Yb, Y;
Medium Rare Earth Elements MREE's = Gd, Eu, Sm;
Light Rare Earths LREE's Ce, La, Pr, Nd.