technical report on the nechalacho deposit, thor lake project ...

In a typical test, for example CCr-27, concentrate was treated with sodium hydroxide at 600°C
for three hours, cooled, then water washed to remove excess sodium hydroxide and the
phosphates and silicates formed in the cracking process. The solids were then leached with
hydrochloric acid and yielded 96% zirconium extraction and more than 96% solubilization of the
rare earths.
Other approaches to the caustic cracking process have been investigated including cracking
tests using sodium carbonate, cracking in an autoclave using strong caustic solution, cracking in
the presence of reductants, and low temperature attrition milling with sodium hydroxide. Some
of these tests provided encouraging results and further tests have been planned.
Another approach to cracking refractory minerals is acid baking in which the feed material is
mixed with concentrated sulphuric acid and held at a temperature of 200°C or more for a few
hours. This method is widely used in China for decomposing the rare earth concentrates from
Bayan Obo and elsewhere.
SGS has investigated the use of acid baking for the Thor Lake concentrate and it has been
seen to solubilize about 80% of the light rare earths and 50% of the heavy rare earths. Zircon
extraction is minimal, less than 4%, even under extreme acid bake conditions clearly indicating
the refractory nature of zircon.
SGS Mineral Services has also investigated the use ammonium sulphate or ammonium chloride
as acid baking reagents. Some elements were extracted but no further work is planned.
A combination of acid baking and caustic cracking has also been investigated and shown to
offer high recoveries and preferred reagent consumption levels and operating costs. As
<strong>report</strong>ed in the previous Technical Report, extractions under favourable conditions are typified
by the results of AB-19 in which overall zirconium recovery was 99%, overall light rare earth
(lanthanum, cerium and neodymium) extraction was 98%, and extraction of the heavy rare
earths and yttrium was 99%. Niobium extraction was 83%
Although it is clear that a very effective process for solubilizing the valuable elements in the
Thor Lake concentrate had been identified, testwork is continuing at SGS Mineral Services to
further define the process parameters and optimize the flowsheet for the initial solubilization
step.
Extracting valuable elements from the refractory minerals of the concentrate is a key part of the
hydrometallurgical process. Once the elements of interest are in solution, it is necessary to
separately recover the zirconium, rare earths, yttrium, niobium and tantalum and this has been
investigated in the laboratory. The flowsheet that was selected for the pre-feasibility study
Technical Report 43-101 – March 13, 2011 Page 16-3
Prepared by Avalon Rare Metals Inc.