This report details the proposed processing route for producing muriate of potash (MOP) from carnallitite mining brine at the Mengo Permit Area.
Report context
This technical report, dated June 2014, addresses the Mengo Permit Area in the Kouilou Region of the Republic of Congo. The processing method described was developed by Changsha Design and Research Institute of Ministry of Chemical Industry during preparation of a feasibility study (CHONFAR 2012) and subsequent basic engineering for detail design (CHONFAR 2013a). The report presents a proposed process flowsheet and material balance delivered by CDI (CHONFAR 2013b) that formed the basis for the process description.
Processing route
Overview
Brine from solution mining is transported to the plant for processing into a wet KCl product, which is then transported as slurry to a drying, compaction, storage and port facility at the coast. The potash processing plant is designed to produce 1,200,000 tons per year of MOP product of K60 quality, equating to a KCl content of at least 95%. The plant is planned to run 7,600 hours per year, 24 hours a day, with remaining time reserved for scheduled maintenance.
The process comprises six main steps: Carnallite Decomposition, Hot Leaching, KCl Crystallization, Product Drying and Compaction, Brine Evaporation, and Carnallite Crystallization.
Carnallite Decomposition
Mining brine enters the process in decomposition of synthetic Carnallite. Crystallized Carnallite from Section 17.6 is treated with solution mining brine at a temperature of 65-70°C. The mining brine dissolves additional amounts of MgCl₂, causing the Carnallite to dissolve. Simultaneously, solid KCl begins to precipitate as fine crystals because KCl solubility decreases with increasing MgCl₂ content. The increasing MgCl₂ content also decreases NaCl solubility, causing NaCl to crystallize during Carnallite decomposition. Precise adjustment of solid Carnallite and mining brine quantity is described as indispensable.
The decomposition KCl, consisting of a KCl and NaCl mixture, is separated from the MgCl₂-rich brine. The MgCl₂-rich brine is sent to Evaporation (Section 17.5) to recover contained KCl as synthetic Carnallite. The KCl/NaCl mixture proceeds to Hot Leaching (Section 17.2).
Hot Leaching
The KCl/NaCl mixture from Carnallite Decomposition is treated with hot leaching brine from Section 17.3 to dissolve contained KCl completely. KCl solubility increases with temperature of the leaching solvent, while NaCl solubility is only slightly raised, so most NaCl remains in solid state. The resulting brine is saturated in both KCl and NaCl at a temperature of 95-102°C.
Mother liquor from KCl crystallization, undersaturated in KCl, is used as leaching brine. After pre-warming with vapours from crystallization via heat exchangers, the brine is finally heated to approximately 115°C with live steam. The hot leaching suspension undergoes solid-liquid separation. The clarified hot brine is transferred to KCl crystallization (Section 17.3), and the solid NaCl is stockpiled.
KCl Crystallization
The clarified brine from hot leaching is cooled stepwise to a final temperature of about 45°C using a 5-effect vacuum cooling crystallization system. Water is evaporated by applying vacuum, cooling the brine. KCl crystallizes due to significantly decreased solubility at lower temperatures. NaCl can be kept in solution by adding a small amount of water to each crystallization stage. MgCl₂ remains well soluble and does not crystallize at this step.
The suspension undergoes solid-liquid separation, and the solid KCl is de-brined to reduce adherent brine, which influences final KCl product quality. The separated mother liquor is pre-warmed with generated vapours from previous crystallization stages using heat exchangers and re-utilized as hot leaching brine (Section 17.2).
Product Drying and Compaction
The product drying and compaction plant is located in a separate facility approximately 19 km from the main processing plant. De-brined KCl from Section 17.3 is mixed with saturated KCl brine and transferred via pipelines to the compaction plant. At the plant, KCl is de-brined and subjected to natural gas operated dryers where water content is reduced to at least 0.2% to meet K60 MOP specifications. The dried product is granulated and colored with iron (III) oxide as needed, then transported to product storage.
Brine Evaporation
After Carnallite Decomposition, the brine has a relatively high KCl content that must be partly recovered. The brine is subjected to 3-effect evaporation. Upon heating to over 100°C, water is evaporated and the brine becomes further concentrated. During heating and water removal, solid NaCl crystallizes as NaCl solubility is nearly temperature-independent. NaCl is separated from the hot brine and conveyed to a stockpile; the hot brine proceeds to Carnallite Crystallization (Section 17.6).
Carnallite Crystallization
The hot brine from Brine Evaporation, saturated with KCl and NaCl, is subjected to a 3-effect vacuum cooling system where brine temperature is reduced to approximately 60°C along with water evaporation. Due to the high MgCl₂ content, Carnallite crystallizes along with some NaCl. The crystallized material mainly consists of synthetic Carnallite. Some vapours from this crystallization can be utilized for heat recovery via heat exchangers.
The synthetic Carnallite is separated, de-brined, and re-introduced into the process at Carnallite Decomposition (Section 17.1). The residual high MgCl₂ brine is used for preparation of hot solvent for solution mining and discharged from the process, removing the major part of MgCl₂ that entered via mining brine. Since this brine is saturated with KCl and NaCl, some KCl is disposed of and considered as product losses.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Annual MOP production capacity | 1,200,000 tons | Design |
| Product quality | K60 (≥95% KCl) | Design |
| Annual operating hours | 7,600 hours | Design |
| Daily operation | 24 hours per day | Design |
| KCl recovery rate | 89.2% | Design (mass balance) |
| Carnallite decomposition temperature | 65-70°C | Design |
| Hot leaching brine temperature | 95-102°C | Design |
| Hot leaching final heating temperature | ~115°C | Design |
| KCl crystallization final temperature | ~45°C | Design |
| KCl crystallization system | 5-effect vacuum cooling | Design |
| Brine evaporation system | 3-effect evaporation | Design |
| Carnallite crystallization system | 3-effect vacuum cooling | Design |
| Carnallite crystallization final temperature | ~60°C | Design |
| Product drying water content target | ≤0.2% | Design |
| Distance to separate drying/compaction facility | ~19 km | Design |
Project website: https://ca.finance.yahoo.com/news/magindustries-corp-ni-43-101-200900319.html
Technical qualifications
The process description is based on a simplified process flowsheet and material balance delivered by CDI (CHONFAR 2013b). The report states that in the opinion of the authors, the presented process and recovery rates are technically feasible and can be used for CAPEX and OPEX estimation as basis for an economic evaluation required for Mineral Reserve estimation. The KCl recovery rate of 89.2% includes all losses from production of mining brine to storage of product for shipment at the port site. No historical operating data or testwork results for the processing plant are presented in this section of the report.
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Source: Update of the NI 43-101 Technical Report for MagMineral's Mengo Permit Area, Kouilou Region, Republic of Congo, June 2014, Section 17 Recovery Methods.
