Historically, ore from the Kutessay II resource was crushed to a powder, then put through a floatation process to creat a RE concentrate. Stans Energy will be testing new milling technologies at a pilot scale in 2011 to attempt to improve upon the historical milling process.
Kyrgyz Chemical-Metallurgical Plant Separation Process
The Kashka REE Plant (formerly known as the Kyrgyz Chemical-Metallurgical Plant) was designed to process concentrate from Stans’ 100% owned, former REE mine, Kutessay II. Stans Energy Corp. is currently engaging VNIIHT experts from Moscow Russia to assess the state of the Kaskhka REE Plant (KRP), and evaluate the plant’s capacity in relation to potential Kutessay II plans. The assessment will include proposed methods of improving the historical process, to optimize the plants with modern technology. The block diagram below shows the historical flow of production of the main intermediate materials and the final products produced by KRP while it was in operation.
Historical REE Production Flowsheet
(click to view full size)
Processing Facilities Summary
Rare Earth (RE) concentrate from the Kutessay II mine was brought to KRP by truck.
The KRP facility included four main departments: Plant 1, Plant 2, Plant 3 and Plant 4, whose primary functions were:
Plant 1 – conversion of RE mineral concentrate into their soluble form, primary RE dissolution and solvent extraction. These processes create the mixed RE solution.
Plant 2 – separation of the mixed RE solution from Plant 1 into streams of Light RE concentrate (solution), Middle RE concentrate, Heavy RE concentrate and the final product -Yttrium Oxide.
Plant 3 – separation of the Middle and Heavy RE concentrates from Plant 2 into the individual RE Oxides (as products); RE Metals and Alloys (as products).
Plant 4 – separation of the Light RE concentrate from Plant 2 into the individual RE Oxides (as products).
Note: Plant 4 is not under Stans’ option, and has been stripped of its processing materials.
Plant 1 – Cracking and Dissolution of the Rare Earths
In Plant 1, the Ore concentrate containing 6.0 -7.0% total Rare Earths (including about 2% Yttrium Oxide) was mixed with Soda Ash (Na2C03 and ‘cracked’ (calcined in a rotary kiln) to release the REO for dissolution in dilute nitric acid. Water was added to the calcined mixture which was then ground in a mill operating in closed circuit with a classifier to separate the ground from the ungrounded material.
The ground solids were settled and thickened in two thickeners and the solids separated from the thickener underflow with a vacuum drum filter. The overflow from the thickeners and the filtrate were neutralized and discarded to waste.
The solids were then reacted with nitric acid in a series of reactors to dissolve the Rare Earths. The reaction products pulp was fed to a solvent extraction section using rotary disk horizontal extractors and 100% TBP as the solvent. The suspension of raffinate (waste stream) was neutralized with milk of lime and sent to the waste pond. The loaded solvent was washed in similar extractors and the product solution containing the RE – nitrates was transferred to a further set of reactors to precipitate and remove any traces of Calcium, Sodium, Ammonia, Zirconium and Thorium from the RE solution. Solids were removed on a plate and frame pressure filter or by centrifuging.
The reaction product was then cleaned in a series of mixer settlers arranged in cascades using C7- C9 based Fatty acids to extract all traces of the contaminants from the RE -nitrates solution. Part of the RE – nitrates solution was recycled back to the mixer settler cascade in order to maintain the purity of solution.
Plant 2 – Extraction of Yttrium and Mixed Light, Middle and Heavy Rare Earths
The RE – concentrate (RE – nitrates solution) from Plant 1 was transferred in containers to Plant 2.
Plant 2 consisted of five separate mixer settler cascades and evaporation batteries designed to initially separate the RE solution into the Light, Middle and Heavy Rare Earths (LREEs, MREEs, HREEs) and to produce Yttrium Oxide as a finished product.
The RE solution from Plant 1 was first concentrated to 300g/l dissolved REs before feeding to the extraction section.
Each mixer settler cascade (battery) in this section consisted of between 80 to 120 mixer settlers for the extraction of the REs into the 100% TBP solvent at an Organic:Aqueous (0:A) Ratio of 20:1. Subsequent stripping of the loaded TBP solvent washed the various RE fractions back into the Aqueous Phase. Three mixer settler cascades were used to separate the REs into the three main fractions LREE, MREE, and HREE concentrates and Yttrium.
The fourth and fifth batteries were used for preconcentration of Dysprosium (Dy), Samarium (Sm), Europium (Eu), before Plant 3, depending on inner requirements of the departments of the KRP facility.
The stripped aqueous solution contained about 100g/l REs and was concentrated to 300g/l by evaporation.
The Yttrium was then precipitated as the Oxalate. The pure Yttrium Oxalate solids were filtered and washed on a simple Neutsch filter. Batches of filter cake were dried at 150-300°C for 3 hours and then calcined at 800°C for 8 hours to obtain the pure Yttrium Oxide (Y203). Approximately 90% of the Yttrium Oxide produced was at 99.99% purity and 10% at 99.95% purity.
Plant 3 – Separation of the Heavy and Light Rare Earths
Plant 3 separated MREE and HREE fractions into the individual RE Oxides by Ion Exchange Technology.
The Plant consisted of a solution preparation section where the various complexing, elutriation and regeneration solutions were prepared. The process was carried out on a batch system where the conditions in the ion exchange column (linear flow, solution, complexing, elutriating solution, concentration solution, etc.) were specific for each REE.
The Rare Earths were then precipitated as the oxalate (carbonate), filtered and washed and then dried and calcined to REO.
RE purities ranged from 99.5% to 99.99%.
Plant 3 – Hydro Metallurgy Section
The Hydro Metallurgy section involved the production of RE Metals (REMs) from REOs. The REMs were produced according to the marketing plan, the demand and potential sales of RE as the higher value Metal instead of as Oxides. Purities ranged from 99.0% to 99.99%, depending on order specifications.
Various electrical, induction and arc furnaces were available to produce the various RE alloys as required.