I-Minerals' March 2016 feasibility study for the Bovill kaolin project in Latah County, Idaho, combines spiral classification, rod milling, flotation, centrifuge fractionation and calcining, with filtered dry-stack tailings.
The NI 43-101 Technical Report, Feasibility Study, Bovill Kaolin Project, Latah County, Idaho, was compiled by GBM Engineers with Mine Development Associates, HDR, SRK and Tetra Tech for I-Minerals USA, Inc., with an effective date of March 17, 2016. The design is an engineering refinement of the basic design in the prefeasibility study. According to the report, the testwork showed the valuable components can be separated and upgraded in a series of conventional unit operations into high-purity products. The plant produces six main products: metakaolin, standard-grade halloysite, high-purity halloysite, K-feldspar sand in several sizes, Q1 quartz sand in several sizes, and Q3 quartz sand. Q2-grade quartz can also be made but was dropped from the product mix because of limited market demand.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | March 17, 2016 | Not applicable | GBM Engineers for I-Minerals USA, Inc. |
| Products | Metakaolin, two halloysite grades, K-feldspar, Q1 and Q3 quartz | Not applicable | Q2 quartz not in the product mix |
| Crushing | Single crusher in open circuit | Not applicable | Not applicable |
| Clay/sand separation | Two spiral classifiers | Not applicable | With screening and attrition scrubbing |
| Sand grinding | Rod mill with hydrosizer at 30 mesh | Not applicable | Deslimed at 200 mesh |
| Clay cut | Minus 20 | µm | 3 inch hydrocyclones |
| Standard halloysite purity | 70% and above | Not applicable | From the fractionation centrifuge |
| High-purity halloysite | 90% and above | Not applicable | Differential flotation in batch tanks |
| Q3 quartz size | About 50 | mesh | Native size |
| Tailings | Pressure filtered, dry stack | Not applicable | Separate sand and clay thickeners |
Overview
The plant has four main areas: ROM stockpiling and crushing, clay/sand separation, a feldspathic sand circuit that makes quartz and K-feldspar, and a clay circuit that makes kaolin and halloysite. Trucks bring ore from the nearby mining areas to the ROM stockpile, and a front-end loader feeds the crusher.
Key Process Stages
Clay/sand separation. Two spiral classifiers separate the lighter, finer clays from the denser, coarser feldspar and quartz. Further screening and attrition scrubbing free more clay from the sand. Fine sand and residual clay that cannot be processed further go to tailings.
Feldspathic sand circuit. The sands are rod milled in closed circuit with a hydrosizer at 30 mesh, attrition scrubbed and deslimed at 200 mesh in a hydrocyclone. Iron flotation floats off the iron impurities while the sands sink. Flotation then splits the sand: K-feldspar floats to the K-feldspar circuit and quartz sinks to the quartz circuit.
K-feldspar. The feldspar is filtered and dried, cleaned of magnetic material with rare earth magnets (REMs), and fine ground to the required sizes.
Quartz. Quartz is rod milled in closed circuit and split between Q1 and Q3 according to market demand. Q1 is floated to remove residual K-feldspar, then filtered, dried, cleaned with REMs and ground to the sizes users need. Q3 goes through one iron flotation and two spar flotation stages, then filtration, drying and magnetic cleaning, and is sold at its native size of about 50 mesh.
Kaolin. The clays are upgraded in 3 inch hydrocyclones to a minus 20 µm cut. A fractionation centrifuge separates halloysite from kaolin, because halloysite has a lower apparent particle density. The kaolin is acid conditioned to aid filtration, then filtered, dried, pulverized and calcined to metakaolin. Because the metakaolin market is strong, all the kaolin is converted.
Halloysite. The centrifuge product is standard-grade halloysite at 70% or higher purity. It can be upgraded to high-purity halloysite (90% or higher) by differential flotation in batch tanks, where entrained kaolin settles and is recycled to the centrifuge. The product is then cleaned by magnetic separation, acid conditioned, filtered, dried and pulverized. The two halloysite grades are made in campaigns on the same equipment.
Tailings. Sand and clay tailings go to separate thickeners, each fed with quicklime for neutralization. Sand thickener overflow carries flotation reagents and is recycled only to the sand circuit. Clay thickener overflow, which is relatively clean, goes back to the clay circuit. The combined underflows are pressure filtered to a low-moisture cake for the dry-stack tailings area next to the plant.
Additional Interesting Data and Summary
The quartz circuits can vary the split between Q1 and Q3 to suit demand, and the Q1 product is ground to different sizes for different end users.
In summary, the 2016 Bovill feasibility study is an industrial minerals flowsheet rather than a metal recovery plant. It separates one clay-sand ore into six saleable products by classification, rod milling, multi-stage flotation, centrifuge fractionation, magnetic cleaning and calcining, and it keeps the water from its two circuits separate.
Key Processes
- Open-circuit crushing
- Spiral classification and attrition scrubbing (clay/sand separation)
- Rod milling, hydrosizing and desliming of sands
- Iron, feldspar and spar flotation
- Rare earth magnet cleaning and fine grinding
- Hydrocyclone classification and centrifuge fractionation of clays
- Differential flotation of halloysite
- Kaolin calcining to metakaolin
- Segregated thickening and pressure filtration for dry-stack tailings
Source: Bovill Kaolin Project, Latah County, Idaho, USA, NI 43-101 Technical Report – Feasibility Study, compiled by GBM Engineers for I-Minerals USA, Inc., effective date March 17, 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.
Bovill Kaolin Project — 2014 Technical Report
A technical report summarizing processing methods, proposed flowsheet, historical testwork recoveries, and design criteria for the Bovill Kaolin project.
Report context
This report, dated June 26, 2014, presents the recovery methods, processing route, plant design, and consumable requirements for the Bovill Kaolin project. The mineral leases held by I-Minerals are underlain by the Thatuna granodiorite, a source of feldspar with significant sodium oxide (Na₂O) component. The weathering of granitoid ore bodies formed residual (or primary) deposits of kaolin, which also contain K-feldspar and quartz. The clay contains both kaolinite and halloysite (aluminosilicate clay minerals) with the empirical formula Al₂Si₂O₅(OH)₄.
Processing route
Ore Processing
Run-of-mine ore is stockpiled and fed through a crusher for size reduction. The crushed ore undergoes attrition scrubbing with a dosed dispersant, followed by classification in screw classifiers. The screw classifier underflow passes to a Derrick Hi-Cap dewatering screen; the oversize is recovered as feldspathic sands. The overflow from the screw classifier goes to a Derrick Linear Motion Sizing Screen, and the oversize reports as tailings (+325 mesh).
Halloysite/Kaolin Clay Processing
The diluted Linear Motion Sizing Screen underflow is sent to 3-inch diameter cyclones. The cyclone underflow (fine grit) goes to tailings, while the overflow proceeds to fractionation solid bowl decanter centrifuges in a two-pass arrangement. The second-pass centrifuge overflow (halloysite) feeds a dewatering centrifuge; the effluent is recycled and the cake slurry goes to a filter. The halloysite filter cake is dried and packaged. The underflows from both fractionation centrifuge passes (kaolin) are combined, dewatered, filtered, and dried for packaging or sent to a calciner operating at approximately 900°C to produce metakaolin.
Feldspathic Sand Processing
Dewatered feldspathic sands are stockpiled, ground in a rod mill, and classified with a hydrosizer. The classified sands are attrition-scrubbed with dispersant, deslimed in a hydrocyclone, conditioned with flotation reagents, and subjected to iron flotation. The iron flotation tailings are deslimed again.
Potassium Feldspar Processing
The iron flotation tailings are conditioned with flotation reagents and processed through potassium feldspar (K-spar) flotation. The K-spar product is dewatered using horizontal vacuum belt filtration and a fluid bed dryer. The dried product undergoes final upgrading with rare earth magnetic separators and may be fine ground using an air-swept stirred media mill and air classifier before packaging.
Quartz Grade Processing
Quartz 1 grade material is produced from feldspar flotation tailings that are deslimed, reground in a rod mill, classified with a hydrosizer, attrition-scrubbed with dispersant, conditioned with flotation reagents, and subjected to quartz flotation. The product is dewatered using horizontal vacuum belt filtration and a fluid bed dryer, then upgraded with rare earth magnetic separators, and packaged or fine ground.
Quartz 2 and Quartz 3 grades are produced from the Quartz 1 grade fraction through additional iron flotation and subsequent flotation steps. Each grade is dewatered, dried, upgraded with rare earth magnetic separators, and packaged.
Additional Tests and Recommendations
I-Minerals are engaged in continuing evaluation of alternative equipment options to improve the clay circuit by product quality and reduce overall capital equipment costs, including centrifuge optimization, alternative separation techniques, pH adjustment and flocculation for clay filtration, and dryer optimization. Packaging methods include 50 lb Kraft bags, supersacks, and fiberboard containers for kaolin clay. Halloysite nanotubes will be packaged per customer requirements yet to be determined. Product development of halloysite, metakaolin, K-spar, and quartz products continues per market development requirements.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Clay circuit feed split | Approximately 30% of feed to clay separation circuit; remainder to feldspathic sand circuit | Testwork (pilot-scale) |
| Overall clay recovery (based on overall feed) | 22.6% | Testwork (material balance from pilot-scale testing at GMT and MRL) |
| Halloysite product recovery (based on overall feed) | Approximately 7% | Testwork |
| Kaolinite product recovery (based on overall feed) | Approximately 15.6% | Testwork |
| K-spar recovery (from feldspathic sand circuit feed) | Approximately 18% | Testwork |
| Quartz products recovery (from feldspathic sand circuit feed) | Over 50% | Testwork |
| Quartz 1 yield (from feldspathic sand circuit feed) | 25.2% | Testwork (yearly operating criteria) |
| Quartz 1 overall recovery (based on ore) | 17.6% | Testwork |
| Quartz 2 yield (from feldspathic sand circuit feed) | 14.4% | Testwork (yearly operating criteria) |
| Quartz 2 overall recovery (based on ore) | 10.1% | Testwork |
| Quartz 3 yield (from feldspathic sand circuit feed) | 11.1% | Testwork (yearly operating criteria) |
| Quartz 3 overall recovery (based on ore) | 7.8% | Testwork |
| Operating hours per year | 7,812 hours (24 hours/day, 7 days/week, 50 weeks/year, 93% operating efficiency) | Design criteria |
| Minimum halloysite production (clay circuit) | 15,000 t/y | Design criteria |
| Minimum K-spar production (feldspathic sand circuit) | 28,000 t/y | Design criteria |
| Calciner operating temperature | Approximately 900°C | Testwork |
| 3-inch cyclone feed rate | Approximately 31 gpm at 8 to 10 psi inlet pressure | Design specification |
| 3-inch cyclone cut size | Approximately 20 μm | Design specification |
Project website: https://www.mining-technology.com/projects/bovill-kaolin-project-idaho/
Technical qualifications
The material balance for the process was based on the extensive laboratory and pilot plant scale testing studies performed and described in detail in Section 13 of the original document. The data criteria used to develop a material balance was based primarily on the pilot-scale testing performed at GMT and MRL. The yield and recovery values were based on yearly operating criteria developed through the desired product matrix, not hourly, due to the fact that actual hourly production operating criteria allows only for either Quartz 1 and Quartz 2 production or Quartz 1 and Quartz 3 production.
Source: Bovill Kaolin Project , 2014 Technical Report, Section 17 Recovery Methods.
