Stirred-tank bioleaching of nickel and cobalt from pyrrhotite-rich tailings from Sudbury, Ontario

High-pyrrhotite tailings are highly reactive and can easily oxidize and produce acidity and/or metal-laden drainage under some disposal conditions, while at the same time this material may contain significant metal values. CanmetMINING is currently developing a stirred-tank bioleaching process to recover nickel and cobalt (both critical for electric vehicle batteries) from pyrrhotite-rich tailings. This manuscript reports on the process development with one sample from the Sudbury region, which includes: mineralogical and chemical characterization; magnetic separation; comparison of abiotic, biotic, and anoxic leaching to identify different dissolution mechanisms; and a comprehensive stirred-tank bioleaching study to determine the effect of pH (1.6 to 3) and temperature (30 to 50 degrees C) on the dissolution of nickel and cobalt. The sample was determined to contain 0.59% nickel and 0.017% cobalt, primarily in pyrrhotite and pentlandite (similar to 51 and similar to 1 wt% respectively). Following magnetic separation, the magnetic fraction contained approximately 50% higher nickel content compared to that of the non-magnetic fraction; enrichment was limited by the fact the residual non-magnetic pentlandite was essentially split between the two fractions. Stirred-tank bioleaching experiments resulted in 80 to 90% and 70 to 80% leaching of nickel and cobalt respectively in 10 days at T >= 40 degrees C; suggesting a very robust process. A novel bioleaching process at elevated pH (similar to 3) that incorporates iron removal in the bioleaching circuit has been discussed; there are significant potential capital and operation cost savings.

Automated summary

This study presents the development of a stirred-tank bioleaching process by CanmetMINING for recovering nickel and cobalt from pyrrhotite-rich tailings. The experiments showed high efficiency and robustness of the process, offering a significant potential for resource recovery and cost savings.