Improving understanding of nickel leaching from petroleum coke in Canada’s oil sands region

Leaching of nickel and other metals from petroleum coke generated in Canada’s oil sands region may pose a risk to water quality.

Petroleum coke is a bitumen upgrading byproduct that is produced during conversion of bitumen into synthetic crude oil. Over eighteen thousand tonnes of this byproduct are generated daily in the Athabasca Oil Sands Region (AOSR) in northern Alberta, Canada and roughly 90% of petroleum coke is stored on site at mines in large deposits.

Using X-ray technology, we found that most of the nickel in fluid petroleum coke deposits is strongly bound to carbon and not likely to leach out. But a small proportion of nickel is more weakly bound to sulfur, oxygen, and other chemical elements present in coke. Nickel leaching is likely associated with the more weakly bound fraction, which may explain why only a small portion of the nickel is readily leached from fluid petroleum coke into water.

When we analyzed water samples collected from the deposits, we found nickel leaching is enhanced when fluid petroleum coke is in contact with slightly acidic waters, such as rainwater, compared with the slightly alkaline waters that are typical of oil sands tailings ponds.

Our research on chemical forms of nickel present in petroleum coke and the conditions under which nickel leaches into water can inform planning for the closure of oil sands mines.

Read the full paper — Nickel geochemistry of oil sands fluid petroleum coke deposits, Alberta, Canada by Jake A. Nesbitt, Jared M. Robertson, Lawrence A. Swerhone and Matthew B. J. Lindsay on the FACETS website.