Recovery of critical minerals from mine tailingsintegrated with CO2 mineralization

The mining of critical minerals (CMs) is a paramount for the development of advanced renewable energy systems and storage technologies. CMs are found in ores located only in a few areas of the world and are extracted often through inefficient and unsustainable processes. Their current supply
will not be able to meet future demand. Therefore, their mining with innovative and sustainable solutions from alternative and more widely distributed resources such as waste is envisaged.
Here we present results of a research aimed at developing a process for the extraction of CMs integrated with ex situ carbon dioxide (CO₂) mineralization to transform mining into a carbonnegative operation. The mine tailings acquired from a wollastonite mine (NY, USA) were used as a
waste source material. The tailings contain three major minerals: wollastonite (CaSiO₃), diopside (MgCaSi₂O₆), and garnets (grossular Ca₃Al₂(SiO₄)₃ and andradite Ca₃Fe₂Si₃O₁₂). Enhanced mineral dissolution of the waste was carried out using a flow-through system, with 0.1 m of formic acid as
organic catalyst and at 40 and 80^oC. The extracted elementes were then separated using nanofiltration to create two streams. One containing CM (namely Al, Fe, Mg, and Mn) and the other rich in Ca for CO₂ mineralization. Nanofiltration was performed by a commercial polyether sulfone (PES)
membranes modified via interfacial polymerization method to separate multivalent cations from the leachate. Data from tests were used to validate a process model that combines population balance equation, the one-dimensional (1D) Poisson-Nernst-Planck (PNP) equation, and geochemistry. The
model agrees well with the data and shows that the integrated process reaches steady state within 48 hours with dissolution achieving completion in one day at 80^oC and nanofiltration obtaining 98 % for the separation of Ca and Mn in a few hours.