Rio Tinto disclosed to the Australian Securities Exchange (ASX) a maiden Ore Reserve and updated Mineral Resource at its 100% owned Jadar lithium-borates project in western Serbia. (Earlier post.)

• Ore reserves are valuable and legally, economically, and technically feasible to extract.

• Mineral resources are potentially valuable, and for which reasonable prospects exist for eventual economic extraction.

Rio Tinto said the Ore Reserve is 16.6 Mt at 1.81% Li₂O and 13.4% B₂O₃.

The Mineral Resource underlying the maiden Ore Reserve has been updated to incorporate additional drilling which resulted in an updated geological model. Mineral Resources are reported exclusive of Ore Reserves.

The Mineral Resource comprises 55.2 Mt of Indicated Resource at 1.68% Li₂O and 17.9% B₂O₃ with an additional 84.1 Mt of Inferred Resource at 1.84% Li₂O and 12.6% B₂O₃.

The update precedes the release of the project’s ‘Elaborate of Resources and Reserves’, reporting required under the Serbian Reporting Code YU53/79. Declaration of resources and reserves is an important milestone as the project progresses towards the award of an exploitation license, the precursor to a construction licence.

Pre-feasibility studies have shown that the Jadar project has the potential to produce both battery-grade lithium carbonate and boric acid. The deposit is located on the doorstep of the European Union, one of the fastest growing electric vehicle (EV) markets in the world, and has the potential to provide lithium products into the EV value chain for decades.

Boric acid is a key raw material for advanced glass and fertilizer products and would be integrated with and complimentary to Rio Tinto’s established position in this market. The scale and high grade nature of the Jadar mineralization provides the potential for a long-life operation in the first quartile of the industry cost curve for both products.

The project under study consists of an underground mine, sustainable industrial processing and waste facilities as well as associated infrastructure.

Jadar, one of the largest greenfield lithium projects in development, would be capable of producing approximately 55 thousand tonnes of battery grade lithium carbonate, as well as 160 thousand tonnes of boric acid (B₂O₃ units) and 255 thousand tonnes of sodium sulfate as by-products per annum. It represents a significant investment for Serbia with both direct and indirect economic benefits, and would become the country’s second largest exporter.

At the end of July 2020, the project moved into feasibility study, with an investment of almost $200 million on a scope that includes detailed engineering, land acquisition, workforce and supply preparation for construction, permitting and the early infrastructure development. The feasibility study is expected to be complete at the end of 2021 and, if approved, construction could take up to 4 years.

Economic assumptions. The grade model used for reporting Jadar Mineral Resources is based on LJZ grade domains defined using a US$300/t contained (Li₂O and B₂O₃) cut-off grade (COG), with the lithium oxide and borate dollar values based on 2019 internal pricing forecast and projected operating costs. The US$300/t COG represents a natural break in the grade distribution between the modeled and reported higher grade jadarite mineralization and lower grade background material. The LJZ grade model consists of 13 domains, which has resulted in elevation and dip differences between the faulted blocks that require separate estimation runs within each faulted block to correctly estimate resource model block grades.

As jadarite is a new mineral to the mining industry, it was important to demonstrate that the ore can be processed economically. Significant processing studies have been undertaken and it has been demonstrated from pilot plant studies that the jadarite can be processed economically with high recoveries. Thus, the JORC requirement for “reasonable prospects for eventual economic extraction” can be reasonably justified, Rio Tinto said.

Comminution and beneficiation involves taking advantage of the hardness differential between the hard jadarite particles and the much softer host rock to produce a 4 mm/+0.2 mm jadarite concentrate, with the -0.2 mm fraction rejected as beneficiation residue. The circuit comprises conventional comminution and classification unit operations, including a high pressure grinding roll (HPGR) which is the key unit operation in this section.

HPGR testing has been performed in a near commercial-scale unit, using a range of ore composites generated from various size drill core across the resource to understand the behavior of jadarite mineralized material. Jadarite concentrate generated is then used in subsequent hydrometallurgical process test work and piloting.

Hydrometallurgical processing involves the initial digestion (leaching) of the concentrate using sulfuric acid. Jadarite can be digested in a dilute sulfuric acid solution; it does not require calcination as a pre-treatment. The consumption of sulfuric acid is predictable with negligible chemical reaction of most gangue minerals—apart from a portion of the carbonates and soluble chlorides. This allows the downstream processing of the pregnant liquor produced from the digestion stage to be a combination of conventional boric acid, lithium carbonate and anhydrous sodium sulfate production processes.

The hydrometallurgical process has been successfully piloted in three separate campaigns at a scale of 5 to 8 kg/h-concentrate in continuous closed circuit mode. The campaigns successfully produced unrefined lithium carbonate, boric acid and sodium sulfate at target recoveries without the build-up of detrimental species.

A large portion of the unrefined lithium carbonate produced in the piloting was refined in a separate small-scale continuous testing campaign via a standard bicarbonation process to produce battery-grade lithium carbonate.