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

The crushing plant is designed for the expansion tonnage. The grinding circuit will require the
addition of a second ball mill to handle the expansion tonnage. Additional flotation cells, gravity
separation units and filters will also be needed.
In the proposed operation, full concentrate containers are stored at the hydrometallurgical
facility and retrieved and placed in a thaw shed as required. The concentrate is thawed and
then dumped into reclaim system that conveys the material into the hydrometallurgical plant.
Concentrate is “cracked” using a combination of acid baking, caustic cracking, and leaching
using sulphuric acid and sodium hydroxide as the primary reagents.
The solid residue from the cracking system is combined with other waste streams and sent to
the hydrometallurgical tailings storage facility. The solution arising from the cracking process is
subjected to double salt precipitation, solution pre-treatment and solvent extraction processes to
isolate the values. Products are precipitated as basic salts, processed and dried to yield
hydrated oxides which are packaged for shipment to markets. Products are be trucked to Hay
River for on-shipment by rail.
The proposed hydrometallurgical process plant consumes a significant quantity of reagents
which will be brought to site by rail to Hay River and then by truck to the plant. Sulphuric acid is
to be produced in a 700 tpd capacity double-contact, double absorption plant from elemental
sulphur. Excess heat from the sulphuric acid plant is used in the hydrometallurgical process in
the thaw shed, to evaporate process solutions, and in the product driers.
Limestone is quarried near Enterprise and crushed and ground to -44 µm for use as a
neutralizing reagent in the process. Some limestone is calcined to lime for neutralizing
purposes.
Other reagents, such as sodium hydroxide, fuel, solvent extraction reagents, etc. are stored at
site as needed.
Most of the hydrometallurgical complex, including the acid plant, is designed and constructed for
the ultimate tonnage equivalent to 2,000 tpd of flotation concentrate. Units requiring duplication
or addition for the expansion tonnage include the thaw shed, acid bake and caustic cracking
facilities, and some of the product driers.
PROCESS DESIGN CRITERIA
The principal design criteria selected for the pre-feasibility study are tabulated in Table 18-12.
The flowsheet used as the basis for flotation recoveries used in the PFS is shown in Figure 18-8
and the flowsheet used as the basis for hydrometallurgical recoveries used in the PFS is shown
in Figure 18-9.
Technical Report 43-101 – March 13, 2011 Page 18-36
Prepared by Avalon Rare Metals Inc.