This technical report describes a proposed processing route for the Banio Potash Project to recover saleable potassium chloride and sodium chloride from solution-mined brines.
Report context
This report is dated June 2024 and presents the recovery methods section for the Banio Potash Project preliminary economic assessment. The project is focused on extracting potash-rich brines from the Banio Project wellfield using solution mining rather than conventional underground mining. The processing section covers proposed design for three production scenarios.
Processing route
Process selection basis
The argument has been made for the use of solution mining in the extraction of potash-rich brines from the Banio Project wellfield, as opposed to conventional underground mining. The proposed processing route avoids the disadvantages of conventional hot leaching or flotation and increases recoveries of the components of the Run of Mine brines.
Proposed process advantages
The proposed process can cope with wide variations in feed composition. Most components of the brines can be extracted and sold as products. The waste product is a harmless magnesium chloride brine in liquid form that can be discharged to sea. No reagents and other chemicals are contained in the waste products. The process can be highly automated and requires a lower number of skilled employees. The process maximises the advantage of having a cheap source of natural gas.
Auxiliary materials and resources
The proposed processing route requires loaded brines directly from the wellfield, or via an intermediate storage tank or clarifier. Fresh demineralised water is sourced from resources close to the MOP plant, industrial mains supply, wells or river. Vapour condensate is recycled from the water evaporation processes. Steam condensate comes from live steam for heating operations. Natural gas is used for power generation, steam raising and product drying.
All water condensate will be collected and re-used in the process facility. Water losses have to be balanced by an external supply of demineralised fresh water. Energy is supplied from live steam at 6 bar from a steam generator unit, powered by waste heat from the power station and supplemented by natural gas flame. Natural gas comes from the under construction gas network, used for steam generation and for direct heating in product drying. Electricity comes from the power station produced from natural gas.
Process steps
The selected and proposed process flowsheet procedure includes dissolution of carnallitite, sylvinite and halite within the brine wells; displacement of loaded brines from the wells to a common collection tank; pumping the brines to the Process Plant Site; receipt of brines into a storage tank or clarifier; heating of brines with steam followed by evaporation; precipitation of purified NaCl solids from evaporators; transfer of brines to a cooling crystalliser circuit; precipitation of KCl solids; debrining and drying of KCl and NaCl solids; compaction of KCl solids, flake crushing and screening; granule post-treatment glazing and oiling; transport of products to storage warehouse; transfer to port as required; and disposal of waste bittern and clarifier tank sediment to sea.
The flowsheet is the same for all three production scenarios, only that the mass balances and number of production units for each will differ.
Fresh water extraction, filtration and injection
Freshwater is abstracted from the Banio Lagoon via a floating pontoon equipped with submersible pumps. The pontoon is connected to land by a floating walkway which also carries the freshwater delivery pipeline and the electricity supply cable. Mesh strainers prevent the ingress of large unwanted solids. The pipeline delivers water to a sand-filtration system to remove unwanted suspended solids which are mostly organic in nature. The sand filtration system can be backwashed into the lagoon periodically.
Filtered freshwater, known as solvent, flows into a wellfield feed tank from where high-pressure, positive displacement pumps distribute the liquid to the wellfield caverns. The pressurized solvent flows into each cavern through one annulus of the drill string and loaded brine flows in the opposite direction, upwards out of the cavern, using the pressure supplied by the solvent. The loaded brine subsequently flows overland to a brine collector tank along with all other loaded brines from the adjacent caverns.
Potash process plant
Loaded brine from the wellfield is received into a large-diameter brine collector tank which offers relatively quiescent conditions for the settling of any fine, insoluble solids which originated in the wellfield caverns. Clarified brine is pumped through a series of heat exchangers which preheat the brine using waste heat from the cooling crystallisers and other sources. The brine temperature is further elevated by live steam injection prior to its introduction to a set of evaporators in parallel.
The evaporation process takes place in vessels which can evaporate approximately 200 t/h water and crystallise approximately 65 t/h NaCl. Evaporation can be conducted using mechanical vapour compression or by steam ejectors. The evaporated water leaves the vessel at the top whereas the precipitated NaCl slurry and concentrated KCl liquid are extracted continuously at the bottom by variable-speed pumps. Heat from the condensate is transferred to the incoming brine via heat exchangers, the condensed liquid is then recycled to the steam-generation boilers.
The NaCl slurry is debrined in solid-bowl decanter centrifuges. The resultant damp solids are dried in a gas-fired, fluidized bed dryer and delivered by conveyor to the product storage warehouse. An application of an anti-caking agent may be added at this stage. The centrate from the centrifuges rejoins the KCl-rich liquid stream from the evaporators.
The KCl-rich streams are transferred to the cooling crystalliser plant and cooled in stages through several vessels from approximately 70 degrees C (minimum 60 degrees C) to approximately 25 degrees C (minimum 20 degrees C). KCl becomes less soluble within this temperature range as the liquid cools, whereas NaCl remains in solution. The liquid is kept boiling as it passes through the crystalliser train because the vacuum pressure increases accordingly. Vacuum can be applied to these vessels using vacuum pumps or steam ejectors. A KCl slurry is extracted from the bottom of each crystalliser which is pumped to the next stage.
The KCl slurry is debrined using solid-bowl decanter centrifuges, the centrate from which is recycled. The damp solids at 5 to 6 percent moisture are fed to a gas-fired fluidized bed dryer, the input air to which can be preheated using power station offgas. Hot MOP exits the dryer at approximately 140 degrees C and is transported by bucket-elevator to the top of the compaction plant for near-immediate compaction or is diverted onto a conveyor for delivery to the product storage warehouse as standard MOP.
Market studies together with requirements indicate that there is a high demand for granular MOP. Such granules are produced from standard grade potash by hot compaction through roller presses. Approximately 90 percent of the total MOP production will be sold as granular fertilizer and about 10 percent of the MOP can be sold in standard quality as dust free KCl with a 0.1 mm to 0.8 mm grain size.
Products
The intended products are saleable grade K60 MOP in both standard and granular form together with a saleable grade industrial vacuum salt containing a minimum of 99 percent NaCl suitable for chemical applications such as the chlor-alkali process. The minimum MOP specification for sale is 60 percent K2O which equates to 95 percent KCl, the remaining impurities are usually NaCl and insolubles such as gypsum and clay.
For the purposes of this preliminary assessment, a conservative assumption has been made that one tonne of NaCl shall be produced for each tonne of MOP. This is conservative because both carnallitite and sylvinite contain high proportions of NaCl. The exact ratio of sylvinite to carnallitite to halite which will be dissolved in the wellfield caverns and hence the final brine composition for each production scenario will only be finalised at the feasibility study stage.
The nominal 100 t/h compactor is capable of producing 40 t/h granular MOP with the balance of 60 t/h recycled within the system, which translates to approximately 300 kt/a with an overall availability of 85 percent.
Product storage
The produced MOP is stored before shipping in a covered shed with a capacity of at least one month's production. The shed will be split to cater for a standard potash pile and a granular pile. These can be delivered to the store by a common overhead conveyor which is run to empty between production campaigns. The two storage areas will be separated by concrete Stelcon walls at the base and have plastic suspended curtaining to prevent dust transfer between the piles. Potash will be placed onto the piles using a Cleveland Cascades chute.
Vacuum salt produced by the process plant may be bagged directly upon production and will not therefore require the same bulk handling requirements as for MOP. Bagging would be conducted in accordance with customer requirements, most likely 1 t woven polythene bags which can be placed on pallets and shrink-wrapped or put into 40 ft containers.
Process alternatives for carnallitic environments
It is well known that the presence of MgCl2 within the leach brine will have an impact on the solubility of the respective Na and K salts within the evaporation and crystallisation environments. In highly carnallitic solutions, it may be required to decompose a synthetic carnallite produced in a later process step in a decomposition evaporator. The decomposition process leads to the crystallisation of a KCl or NaCl mixture and the formation of MgCl2 brine. The synthetic carnallite, intermixed with some NaCl coming from the evaporation and crystallisation unit, must be fed back into a counter-current stream. The requirement to provide a decomposition evaporator followed by a hot leaching tank will be determined during consultation with the selected process engineering provider during future work phases.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| MOP production scenarios | 400 kt/a, 600 kt/a, 800 kt/a | Proposed design |
| MOP product grade | K60 (95% KCl min) | Design specification |
| MOP impurities | Max 5%, predominantly NaCl | Design specification |
| NaCl product purity | >99% NaCl | Design specification |
| Granular MOP target size range | 2 mm to 4 mm | Proposed product specification |
| Standard MOP grain size | 0.1 mm to 0.8 mm | Proposed product specification |
| Granular to standard ratio | Approximately 90:10 | Market indication |
| Evaporation capacity | Approximately 200 t/h water, 65 t/h NaCl per vessel | Design estimate |
| Crystalliser temperature range | 70°C (min 60°C) to 25°C (min 20°C) | Design basis |
| Dryer exit temperature | Approximately 140°C | Design parameter |
| Damp solids moisture content | 5% to 6% | Design parameter before drying |
| Compactor nominal capacity | 100 t/h feed producing 40 t/h granules | Industry standard |
| Compactor overall availability | 85% | Design assumption |
| Storage capacity | Minimum one month production | Design basis |
| Compaction excess capacity | Yes for 400 kt/a and 800 kt/a; No for 600 kt/a | Production scenario analysis |
| Brine production (400 kt/a scenario, peak) | 5.8 M m3/a | Proposed design |
| Brine production (600 kt/a scenario, peak) | 7.8 M m3/a | Proposed design |
| Brine production (800 kt/a scenario, peak) | 11.4 M m3/a | Proposed design |
| Contained KCl (400 kt/a scenario, peak year) | 422 kt/a | Proposed design |
| Contained KCl (600 kt/a scenario, peak year) | 633 kt/a | Proposed design |
| Contained KCl (800 kt/a scenario, peak year) | 844 kt/a | Proposed design |
| Contained NaCl (400 kt/a scenario, peak year) | 980 kt/a | Proposed design |
| Contained NaCl (600 kt/a scenario, peak year) | 1,173 kt/a | Proposed design |
| Contained NaCl (800 kt/a scenario, peak year) | 1,880 kt/a | Proposed design |
| NaCl produced per tonne MOP | 1:1 ratio | Conservative assumption for PEA |
| Product ratio from wellfield | Dependent on final brine composition | To be confirmed at feasibility stage |
Project website: https://millennialpotash.com/project
Technical qualifications
The processing flowsheet recommended in this PEA is designed to produce MOP with a guaranteed purity of 95% KCl (K60) with a maximum of 5% impurities. The exact ratio of sylvinite to carnallitite to halite which will be dissolved in the wellfield caverns and hence the final brine composition for each of the production scenarios will only be finalised at the feasibility study stage when Mineral Resources are converted to Mineral Reserves in keeping with an optimised mine plan.
The requirement for metallurgical testing is described in Section 13 of the report. The dissolving of carnallitic cores from the deposit under controlled conditions will indicate, amongst other things, the final composition of the brine which is to be leached from the caverns. At the later feasibility stage, whether PFS or DFS, the project will seek to engage, directly or indirectly through an engineering contractor, with a specialist evaporation and crystallisation provider who will consider the final leach brine composition in presenting a process solution.
The capital and operating costs of this process route are derived from the intended capacity of each process option using factored capital costs from similar operations and supplemented by Micon's database. Micon is satisfied that both the conceptual process route and costing approach are well within the parameters of the level of definition required by a PEA. Additional capital and operating costs associated with potential modifications for highly carnallitic environments are expected to be well within the level of definition already provided by this study.
Source: Banio Potash Project , 2024 Technical Report, Section 17.0 Recovery Methods, June 2024.
