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Stans Energy improves Kutessay II rare earths concentration with new milling process

Posted on 28 Mar 2011

k_open_pit.jpgToronto-listed Stans Energy Corp is the owner of the Kyrgyz Chemical Metallurgical Plant (KCMP) rare earths (RE) processing complex and associated Kutessay II mine in Kyrgyzstan. The group has announced that is has received a new lab-scale report on Kutessay II metallurgical testing at the concentrate stage. Kutessay II is the only past-producing Heavy Rare Earth Elements (HREEs) mine in the world, located outside of China.This was completed by the Information Research Center LLC (IRC) and reviewed by the leading Russian Research Institute of Chemical Technology (VNIIHT). IRC’s main objectives were to improve upon the historical method of creating rare earth oxide (REO) concentrates from Kutessay II in four main areas – decreasing the costs associated with the historical milling process; recovering additional polymetalic byproducts; increasing the total REO (TREO) content within the concentrate significantly above the historical 6.5% grade, and; increasing the TREO recovery above the historical average of 64%. Two representative samples of the Kutessay II resource were taken for testing, labelled TI and TII. TI was sampled from underground adit No 28, consisting of 10 different areas of the resource in both the north and central zones. TI’s grade was 0.388% TREO. TII was sampled from stockpiled, crushed ore sitting in the bottom of the Kutessay II pit. TII’s grade was 0.565% TREO.

Modern magnetic and gravitational milling techniques were analyzed and tested on both samples. Historical testing completed by Soviet Institutes in the 1980s led IRC to believe that magnetic separation was the best option at the first stage of the milling process after grinding to a grain size of -0.5 mm. Results from magnetic tests on samples TI and TII concluded that magnetic concentration was not the best option for original ore, and instead lab scale gravitational separation provided superior first step results.

However, to properly test the new proposed gravitational concentration process, a pilot scale Falcon concentrator was used. Based on these results, IRC, in association with VNIIHT, came up with a proposed concentration flow sheet to be tested. This new process has been estimated to reduce the amount of processed material by up to 60% after the 1st stage, when compared to the historical method. Lab tests indicate this step has the potential to significantly reduce the historical costs of crushing the ore to a powder, floating, and drying. In by-product terms, tests including magnetic separation were able to achieve recoveries in the concentrate of 80-80.5% silver, 77.5-80% lead, and 84-89% bismuth. Recoveries of zinc and molybdenum ranged from 48% to 57%.

Testing of both samples achieved a TREO content in the concentrate ranging from 13.373% to 19.471%, a significant increase from the historical average of 6.5% TREO. To increase the quality of the final concentrate (removal of ore magnetite and technogenic iron appearing from ball grinding in the ball mill), IRC recommends subjecting the final concentrate to magnetic separation. If the proposed milling process is implemented, and scaled results are similar or better than to lab tests, far less waste rock would have to be trucked to the RE processing complex.

Achieved throughout recovery, with magnetic separation as step 1 and not accounting for additional recoveries from flotation of stage 2 and 3 gravitational tailings, ranged between 47.65% and 51.68% TREO. Gravitational separation tests without magnetic separation achieved recoveries for the individual REE in the range of 50-72%. The proposed 3-stage gravitational separation process will test RE tails after stage 2 and stage 3 for additional REO recoveries through control flotation, calcinations, and chemical dissolution in an attempt to increase recovery numbers. Stans’ pilot scale study in 2011 will determine whether this proposed milling process, or the historical flotation process will be most cost effective.