Scandium International Mining's April 2016 feasibility study for the Nyngan scandium project in New South Wales designs a 75,000 t/a HPAL plant with 83.7% overall scandium recovery.
The Feasibility Study, Nyngan Scandium Project, Bogan Shire, NSW, Australia, NI 43-101 Technical Report, was prepared for Scandium International Mining Corp. with an effective date of April 15, 2016. The plant treats scandium-bearing limonite from Nyngan to produce scandium oxide. The study says the flowsheet was chosen after evaluating the geology, mineralogy and testwork, aiming for a robust treatment method that supports definitive feasibility-level cost estimates. A METSIM model was used for the mass and water balance, with some process chemistry and thickener density assumptions where testwork was unavailable or unreliable.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | April 15, 2016 | Not applicable | Feasibility study for Scandium International Mining Corp. |
| Plant throughput | 75,000 | t/a | 7,500 operating hours a year |
| Overall scandium recovery | 83.7 | % | Not applicable |
| Product grade | Above 99 | % Sc2O3 | Dispatched in small security drums |
| Autoclave temperature | 265 | °C | Continuous HPAL, 25% solids |
| Preheat and letdown | Three stages each | Not applicable | Splash and flash vessels |
| Leach feed density | 38% thickened, 30% autoclave feed | Not applicable | Adjusted with SX raffinate |
| CCD | Eight stages | Not applicable | Underflows at 31% solids |
| Solvent extraction | 3E-1W-2S-1R | Not applicable | Primene JM-T in Shellsol D70 |
| Precipitation | Oxalic acid, 6 m³ batches | Not applicable | Calcined at 900°C |
| Tailings | Neutralized to pH 9, lined storage | Not applicable | Decant reused |
Overview
Ore from the open pit is reclaimed by front-end loader, scrubbed and milled to break up the clay, thickened, and leached with concentrated sulphuric acid in a continuous high-pressure autoclave. The dissolved scandium is washed from the residue in a countercurrent decantation (CCD) circuit, recovered from the pregnant solution by solvent extraction, stripped into a chloride solution, precipitated as scandium oxalate and calcined to scandium oxide. The CCD residue is neutralized and stored in a lined residue storage facility.
Key Process Stages
Ore preparation. A front-end loader feeds ore from the ROM stockpile to a bin, and a belt feeder and conveyor take it to a trommel scrubber that de-agglomerates it. The +10 mm oversize is rejected as coarse rejects. The −10 mm fraction goes to a ball mill in closed circuit with cyclones, with +75 µm underflow returned to the mill and overflow sent to the leach feed thickener.
Leach feed thickening. With flocculant, the thickener raises the slurry to 38% solids. About 20% of the solvent extraction raffinate is added in the HPAL feed storage tanks to reach the 30% solids autoclave feed. Excess high-pressure splash steam preheats the feed to 80°C in a spiral heat exchanger.
High-pressure acid leaching. Three stages of splash vessels heat the slurry further with flash vent steam. High-pressure pumps then feed the autoclave, where steam raises the temperature to 265°C and concentrated sulphuric acid is added. The leached slurry is let down through three flash vessels, with the steam recycled to the splash vessels and any excess vented through a scrubber.
CCD. Eight thickeners wash the scandium from the leach residue. The wash solution, added at CCD No. 8, is raw water, SX raffinate and dirty condensate. CCD No. 1 overflow is the pregnant solution, which is cooled and filtered in sand filters.
Solvent extraction. Three countercurrent extraction stages load a scandium sulphate complex onto Primene JM-T in Shellsol D70. A dilute sulphuric acid scrub washes the organic. Hydrochloric acid with added chloride salt strips the scandium as a chloride complex, and the organic is regenerated with dilute sulphuric acid.
Precipitation and calcination. The strip liquor is filtered through garnet-anthracite and carbon columns and heated to 65°C. Scandium oxalate is precipitated with oxalic acid in 6 m³ day-shift batches, filtered in a plate and frame press, and calcined in a rotary kiln at 900°C. The oxide is washed with deionized water, dried and packed.
Neutralization and tailings. CCD residue is neutralized with lime to pH 2. Sodium hydrosulphide reduces chromium in solution to Cr(III), and two further lime stages raise the pH to 9 to precipitate heavy metals. The slurry is thickened and placed in a lined residue storage facility, whose decant is reused.
Additional Interesting Data and Summary
The plant's main areas are ore preparation, leach feed thickening and storage, HPAL, CCD, solvent extraction, scandium oxalate precipitation, scandium oxide recovery, final neutralization and tailings, reagents and services. The HPAL circuit includes an emergency vent knockout pot and full agitator seal and gland water systems.
In summary, the 2016 Nyngan feasibility study is a small, high-value hydrometallurgical plant. It leaches 75,000 t a year of scandium laterite at 265°C and recovers 83.7% of the scandium as an oxide above 99% purity through CCD, amine solvent extraction and oxalate precipitation.
Key Processes
- Trommel scrubbing and ball milling with cyclones
- Leach feed thickening and raffinate dilution
- Steam preheating in splash vessels
- High-pressure acid leaching at 265°C
- Three-stage flash letdown
- Eight-stage countercurrent decantation
- Amine solvent extraction with hydrochloric acid stripping
- Oxalic acid precipitation and calcination to scandium oxide
- Two-stage lime neutralization and lined residue storage
Source: Feasibility Study – Nyngan Scandium Project, Bogan Shire, NSW, Australia, NI 43-101 Technical Report, prepared for Scandium International Mining Corp., effective date April 15, 2016.
Earlier report summaries
Earlier versions of this profile, based on older technical reports, are retained below for source traceability. Dates and figures reflect each report’s own effective date and are superseded by the current information above.
Technical Report on the Nyngan Scandium Project — 2014
This report documents the feasibility study for the Nyngan Scandium Project, effective October 10, 2014.
Report context
The technical report titled "NI 43-101 F1 Technical Report on the Feasibility of the Nyngan Scandium Project" was prepared for EMC Metals Corp., Sparks, Nevada, with an effective date of October 10, 2014 and an issue date of October 24, 2014. The document number is 14013-0000-PS-RPT-001.
Processing route
Proposed flow sheet
The proposed processing flow sheet consists of feed preparation, high pressure acid leaching, counter-current decantation (CCD) circuit, partial neutralization, solvent extraction, scandium oxide recovery, and final neutralization with tailings management.
Feed preparation (Area 1000)
Feed preparation involves handling and conditioning of the mined material prior to leaching.
Feed thickening (Area 1700)
Feed thickening is conducted to achieve the appropriate solids concentration for the subsequent leaching stage.
High pressure acid leaching (Area 2100)
The high pressure acid leaching (HPAL) circuit treats the thickened feed under elevated temperature and pressure conditions to extract scandium into solution.
CCD circuit (Area 3000)
A counter-current decantation circuit separates the leach solution from the solid residue, with multiple washing stages to maximize scandium recovery.
Partial neutralization (Area 4000)
Partial neutralization of the pregnant leach solution is performed to remove impurities and condition the solution for solvent extraction.
Solvent extraction (Area 5000)
Solvent extraction is used to selectively concentrate and purify scandium from the partially neutralized solution.
Scandium oxide recovery (Area 6000)
Scandium oxide precipitation and recovery produces the final product from the solvent extraction strip solution.
Final neutralization and tailings (Area 7000)
Residual process solutions are neutralized before being sent to the tailings storage facility.
Water management
Water management systems are incorporated to recycle process water and manage site water balance.
Reagents and services
Reagents and services required for the process are detailed in the report.
Test work
The report describes test work programs for acid bake, solvent extraction, scandium oxide precipitation, high pressure acid leach, flotation, and ion exchange.
Acid bake test work
Acid bake test work was conducted to evaluate alternative processing options for scandium extraction.
Solvent extraction test work
Solvent extraction test work was performed to determine extraction efficiencies and reagent requirements.
Scandium oxide precipitation test work
Scandium oxide precipitation test work was carried out to define product purity and recovery conditions.
High pressure acid leach test work
High pressure acid leach test work was completed to confirm the proposed HPAL processing route.
Flotation test work
Flotation test work was undertaken to assess potential for pre-concentration of the feed material.
Ion exchange test work
Ion exchange test work was conducted as an alternative purification method.
Future test work
The report identifies additional test work required for process optimization.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Feed preparation area | Area 1000 | Proposed design |
| Feed thickening area | Area 1700 | Proposed design |
| High pressure acid leaching area | Area 2100 | Proposed design |
| CCD circuit area | Area 3000 | Proposed design |
| Partial neutralization area | Area 4000 | Proposed design |
| Solvent extraction area | Area 5000 | Proposed design |
| Scandium oxide recovery area | Area 6000 | Proposed design |
| Final neutralization and tailings area | Area 7000 | Proposed design |
Project website: https://scandiummining.com/projects/nyngan-scandium-project/
Technical qualifications
The report is a Preliminary Economic Assessment (PEA) and contains a cautionary statement regarding the preliminary nature of the assessment. Specific limitations include the need for future test work to optimize the process, as identified in the report.
Source: NI 43-101 F1 Technical Report on the Feasibility of the Nyngan Scandium Project, effective date October 10, 2014, issue date October 24, 2014, Section 13, Section 17.
