This review outlines the process design for the Penco rare earth project, covering the recovery of rare earth carbonate from ionic clay feed, as described in the December 2021 preliminary economic assessment.
The rare earth carbonate production process for the Penco project is designed around results from test work carried out by the Universities of Concepcion and Toronto, together with batch-scale tests from the Chapi site. The plant is intended to treat an ionic clay mineral containing various lanthanides at a feed rate of 240 wet tonnes per hour. The process design specifies an average production of 1,275 tonnes per year on a dry basis of rare earth carbonate, with a planned feed grade of 2,047 ppm rare earth elements and a fresh mineral moisture content of 16 percent.
The process flowsheet, prepared by Ausenco in 2021, is divided into several operational areas. The leaching solution is not selective; in addition to extracting rare earths, it leaches a range of polluting elements. This requires downstream treatment to precipitate impurities under controlled pH conditions. The design also includes a water recovery system to minimize fresh water consumption and liquid waste, with recovered water returned to the process.
The overall metallurgical performance is driven by the leaching stage and the plant yield. Leaching is specified at 18.49 percent, with a plant yield of 98.1 percent, giving an overall performance of 18.13 percent. Reagent consumption values, provided per tonne of dry feed, include sulfuric acid at 1.063 kilograms, ammonium sulphate at 1.140 kilograms, ammonium bicarbonate at 1.949 kilograms, lime at 0.434 kilograms, and flocculant at 0.121 kilograms. Fresh water consumption for the process plant is stated as 11.7 cubic metres per hour.
The design intentionally restricts liquid residue generation. Apart from water contained in the impregnation of discarded solids, no liquid effluents are planned. This is achieved by recovering water from weak solutions generated in filtration and repulping stages, treating it with reagents and available technologies, and returning it to the process. The carbonation process generates solutions that are sent to the water recovery system, from which part is returned to the leaching process.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Processed wet mineral feed | 240 | t/h | Not stated |
| Dry mineral feed | 202 | t/h | Not stated |
| Fresh mineral moisture | 16 | % | Not stated |
| REE grade | 2,047 | ppm | Not stated |
| Leaching pH | 3-4 | unitless | Not stated |
| Leaching reagent concentration | 0.15 | Molar | Ammonium sulphate |
| Impurities precipitation pH | 5.5-6.0 | unitless | Not stated |
| Carbonate precipitation pH | 7.0-7.5 | unitless | Not stated |
| Dry carbonate production | 1,275 | t/a | Dry basis |
| REE grade | 51.4 | % | Not stated |
| REE2(CO3) grade | 91.9 | % | Not stated |
| Eq REEO grade | 91.9 | % | Not stated |
| Leaching performance | 18.49 | % | Not stated |
| Plant yield | 98.1 | % | Not stated |
| Overall performance | 18.13 | % | Not stated |
| Fresh water consumption | 11.7 | m3/h | Not stated |
| Sulfuric acid (98%) | 1.063 | kg/t dry | Reagent consumption |
| Ammonium sulphate | 1.140 | kg/t dry | Reagent consumption |
| Ammonium bicarbonate | 1.949 | kg/t dry | Reagent consumption |
| Lime | 0.434 | kg/t dry | Reagent consumption |
| Flocculant | 0.121 | kg/t dry | Reagent consumption |
Overview
The Penco project aims to produce rare earth carbonate from ionic clay ore using a hydrometallurgical process. The technical report describes a development-stage project based on laboratory and batch test results, with the flowsheet designed to manage water recovery and limit waste. The process is structured into distinct areas covering ore handling, leaching, impurity removal, carbonation, and water treatment.
Key Process Stages
The plant design includes a wet clay stacking and feeding area where ore is washed in a drum and particles over 10 millimetres are separated and sent to final disposal. The mineral pulp then moves to the leaching area, where a countercurrent decantation circuit is used. Two streams are produced: a mineral sterile pulp that undergoes wet screening to separate a plus 1 millimetre fraction for band filtration and washing, and a sub-1 millimetre pulp that feeds a plate filtration system. Both filtered tailings streams are stacked and later transferred to final disposal.
The strong solution from leaching is sent to the impurities precipitation area, where the pH is not specified for this stage, but the subsequent carbonation step maintains a controlled pH in the range of 7.0 to 7.5. The carbonation process yields the rare earth carbonate product, and the pulp from polishing filters is discharged to a stirred pond for final disposal. Solutions generated during carbonation are directed to the water recovery system, with part of the treated solution returned to the leaching circuit.
The water treatment system is designed to recover water and remove impurities that could affect product quality. It includes chemical precipitation, with nanofiltration, reverse osmosis, and ion exchange listed as technologies under study. Two reverse osmosis plants are considered, with rejected water from RO Plant 2 and treated water from the recovery system feeding a treated water tank. This tank distributes treated water to plant areas that do not require high purity. Clean water for high-purity applications is supplied from a tank that receives fresh water from the Penco water intake and RO water from the treatment system. Fresh water is also directed to a fire system tank for emergency use.
Additional Interesting Data and Summary
The extraction data used for the mass balance was generated from 6,683 drill holes, which were used to develop a mining plan. From this plan, an average mineral feed flow was obtained, accompanied by grade and extraction data for each element. These values were then used to carry out the mass balance. The design parameters were obtained from various laboratory tests and subsequently checked at the Chapi test bench scale.
Reagent preparation is an important part of the plant design. Sulfuric acid is one of the most used reagents on the lanthanide production plant. It is used both in dilute solution preparation and, separately, for compressed air supply lines serving instruments and for compression on plate filters in the leaching, carbonation, and reverse osmosis plant areas. Lime is prepared as a slurry and pumped for use in the impurities precipitation stage of the reverse osmosis plant area.
The detailed procedures for the use of these reagents are listed in the technical report, covering the preparation and application of sulfuric acid, ammonium sulphate, ammonium bicarbonate, lime, and flocculant across the various process stages.
Key Processes
- Leaching: countercurrent decantation circuit with pH 3-4, ammonium sulphate concentration 0.15 molar
- Impurities precipitation: pH 5.5-6.0, using lime slurry
- Carbonate precipitation: pH 7.0-7.5
- Water recovery: chemical precipitation, nanofiltration, reverse osmosis, ion exchange under study
- Filtration: plate filters used in leaching, carbonation, and reverse osmosis plant areas
Source: Amended and Restated NI 43-101 Technical Report , Penco REE Project, 2021.
Editorial note
The technical source states that the process will not generate liquid effluents, yet it also lists fresh water consumption of 11.7 cubic metres per hour and describes clean water and treated water distribution systems that supply process areas. These statements may appear to conflict, but they can be reconciled if the fresh water intake is offset by evaporation or other losses not detailed in the source. The source also provides a plant yield of 98.1 percent, which appears high relative to the overall performance of 18.13 percent; this is explained by the low leaching extraction of 18.49 percent, where a small fraction of rare earths is recovered from ore into solution. The relationship between these figures is clearly defined in the mass balance tables.
Project website: Amended and Restated NI 43-101 Technical Report, Penco REE Project
