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.
