South Harz Potash Limited reported that it has received encouraging results from metallurgical test work completed by K-UTEC AG Salt Technologies (K-UTEC). Test work was performed on core samples collected from drillholes OHM-01 and OHM-02 completed during 2022 within the Ohmgebirge Mining Licence. Results of the metallurgical test work confirm the process route selected for the Ohmgebirge Scoping Study is suitable for processing the ore type expected to be delivered to the mill.

Results confirm a preliminary crushing size of <4mm will enable KCl extraction from the cold leach stage of the process flow design. The selected processing route is expected to achieve production of K60 (agriculture sales grade) MOP that is the standard of the global potash industry. Test work carried out by K-UTEC in their Sondershausen laboratories, located close to the project area, considered the quantity and quality of NaCl (salt) byproduct expected to be produced from future operations.

Results verified the selected process route can produce chemical grade vacuum salt with a purity exceeding 99%. K-UTEC further reported that additional Mg(OH)2 and CaCO3 by-products can be extracted via the selected processing route. A well-established market for chemical grade NaCl, Mg(OH)2 and CaCO3 exists in the NW European area.

Test work informed the composition and character of the resultant waste products and additionally confirmed that process waste is suitable for use as mine backfill material. Further metallurgical and backfill test is planned during 2023. OHMGEBIRGE SCOPING STUDY PROCESS FLOWSHEET: The Ohmgebirge Scoping Study selected an optimal process route of cold leaching followed by evaporation and cooling crystallisation.

The key steps involved in this process flowsheet are: Crushing/milling of ore at surface. Cold leaching of soluble chloride minerals, KCl and NaCl, at approximately 20-25°C with water. Separation of undissolved sulphate minerals and undissolved NaCl and usage as backfilling material.

Clarification of leaching liquor and separation of fines (clay, anhydrite). Mixing of clarified potash liquor with recycled mother liquor and heating this mixed brine to boiling temperature. Evaporation of water with mechanical vapour compression at approximately 110°C. Separation of crystallised NaCl.

Cooling of hot KCl-NaCl liquor in multi-step vacuum crystallisation plant. Separation of obtained KCl-crystalline crop from the mother liquor and preparation of Muriate of Potash (MOP) with a K2O content of 60% to 62%. Recycling of cold KCl-NaCl-mother liquor back to the evaporation process.

CRUSHING AND SCREENING: Test work completed on samples collected from recent drillholes OHM-01 and OHM-02 considered the crushing and milling requirements of the expected ore from the future mine. The results carried out with a crushing size of <4mm resulted in sufficient grain separation to enable dissolution of KCl during the cold leach stage. DISSOLVING AND WASHING: The test work investigated the dissolving kinetics of KCl and NaCl, and MgSO4 and CaSO4 to highlight the optimal cold leach retention times and temperature of the cold leach solvent.

Test work confirmed that weak NaCl brine solution is potentially the best solvent option for the cold leach phase, in comparison to pure demineralised water, which would have an advantageous effect on future water demands for the processing facility. This will be further refined during follow on test work. Characterisation of leach residues was also carried out by K-UTEC, with the results indicating a waste residue composed of 62% NaCl, 18.4% SO4 and 3.1% K2O, and 5.3% H2O using a weak NaCl bine as a solvent at 25oC solvent temperature.

The scoping study envisages that all leach residues will be backfilled into open spaces in the mine, and characterisation and composition of the leach residue confirms that this is feasible. Further optimisation work for the cold leach stage is planned for during 2023 together with comprehensive slurry backfill test work. The resultant brine from the cold leach stage then underwent the brine purification step where NaOH is added to precipitate out Mg(OH)2 and Na2CO3 is added to precipitate out CaCO3.

This purification bench scale test work confirmed the process route as developed in the scoping study. The test work also confirmed the potential for production of Mg(OH)2 and CaCO3 as additional by-products from the operations. EVAPORATION AND CRYSTALLIZATION: Evaporation-crystallisation bench scale test work was carried out on purified leach brine or mother liquor.

The scoping study proposed crystallisation of NaCl be carried out by heating and evaporation and crystallisation of KCl is carried out by cooling. The composition of the KCl-NaCl-Liquors obtained from the cold leach and brine purification stage was near saturation with a ratio between KCl and NaCl approximately 1 to 2. The mother liquor brine was heated up to ~110oC where hot solid-liquid separation of NaCl was achieved at 5 bar pressure. The mother liquor brine was allowed to cool, resulting in the crystallisation of KCl, with cold solid-liquid separation of KCl being carried out under vacuum.

Four cycles of brine recirculation were required to achieve maximum recovery of the KCl and NaCl products. All KCl was crystallised out with a composition close to 60 % K2O without any further washing, which has been included in the scoping study. Further washing guarantees product specifications are reached and may be used to increase product grade to K62.

The crystallised NaCl product direct from the crystalliser achieved an initial grade of ~80 % NaCl, which could satisfy local road de-icing salt requirements without further washing. The scoping study does include an additional washing purification step for NaCl and the test work confirmed that the grade and composition of NaCl after leaching, filter cake washing and drying is ~99.6% NaCl with 0.4% H2O.