The development of a beneficiation process to remove carbonates from lithium sedimentary claystones

Sedimentary claystones found in Nevada have emerged as a new source of lithium. However, processing these claystones faces several challenges due to the significant presence of carbonates such as calcite. These carbonates not only increase acid consumption during leaching but also result in the generation of pure carbon dioxide. Using conventional beneficiation techniques to remove the carbonates from the claystones is challenging because the particle size of the claystones is too fine to allow those techniques to work effectively. Another aspect is that the lithium in these claystones is associated with clay minerals, which are typically deemed gangue in other mineral processing operations, and that there are no readily available processing strategies to recover the clay minerals as valuable minerals. In this study, a beneficiation process involving the use of attrition scrubbing, enhanced gravity separation via a lab-scale Falcon concentrator, and a chemical dispersant was developed to remove calcite from three different sedimentary claystones, including illitic, calcium-rich, and magnesium-rich smectite claystones found in Nevada. The study showed that the light stream of the Falcon concentrator, which is typically considered the waste stream, contained concentrated lithium with less calcite. Significant separations were achieved using the Falcon ultrafine (UF) bowl operated at a maximum speed of 2333 rpm through a two-stage process consisting of roughing and cleaning stages. The most notable separation was observed for the calcium-rich smectite claystone, which yielded a recovery of 84 % lithium with 73 % calcium removal in the final light stream. Although the current investigation was conducted at a lab scale, the findings provide compelling evidence that enhanced gravity-based beneficiation can be a possible route to upgrade the lithium sedimentary claystones to make the downstream extraction more sustainable. • An enhanced gravity separation process can remove calcite from lithium claystones. • Calcite removal depends on claystone type and pretreatment methods. • Magnesium and lithium are associated within the same crystal structure. • Gravity separation cannot effectively remove magnesium.