Revaluing mine waste rock for carbon
capture and storage
Current research at the University of British Columbia, Norman B. Keevil Institute of Mining Engineering
and the Department of Earth and Ocean Science is focusing on harnessing and optimizing a natural
process - Carbon Mineralization, as an industrialized solution to the problem of CO2 storage.
By Dr. Michael Hitch, Assistant Professor, Norman B. Keevil Institute of Mining Engineering

Environmental sustainability and responsibility
has become an integral aspect of modern
industries, and the mining industry in
British Columbia is certainly no exception.
Rising concerns over anthropogenic contributions
to global warming through excessive
greenhouse gas (GHG) emissions are creating
demand to improve environmental practice,
with many new environmental action
plans currently in the works.
While the implementation of these policies
will be an invaluable addition to current
environmental practices, it is important to
assess the economic and financial implications
these regulations will have on the industry.

The process
Recent breakthroughs in sequestration research
have shown that carbon mineralization
is both realistic and technically feasible
practice that may sequester large amounts of
carbon as stable carbonate minerals. In a
thermodynamic context, carbonate minerals
are the most stable form of elemental carbon.
This is extremely important in carbon
capture technologies since leakage, commonly
attributed to other CO2 sequestration
options, is prevented by forming naturally
occurring and inert by-products. Mineral
carbonation simply takes advantage of and
accelerates the natural weathering process of
silicate rock and its tendency to react with
ambient CO2 to form carbonate minerals.
This chemical reaction is represented as follows:
MgSiO2 + CO2 = MgCO3 + SiO2
Mg-silicates are ideal minerals for use
in mineral carbonation. The relatively low
solubility of alkaline earth metals promotes
the fact that sequestered carbon is stable on
a geologic time scale, thus reducing the risk
of CO2 leakage over time and increasing the
storage options available. These metals are
also relatively invaluable in other applications
and are abundantly found worldwide in
silicates.
Nickel mines with their associated
waste materials have proven to provide the

best material for carbon mineralization. That

being said other types of mines also have
significant sequestration potential.
How mine waste rock and tailings play
a role
Historically, materials that do not contain ore
minerals, industrial minerals, metals, coal or
mineral fuels, or when the concentration of
these materials is sub-economic, have been
considered mine waste. These materials
must also contain commodities with a concentration
great enough to be mined profitably.
The notion of cut-off is used to differentiate
waste rock from metalliferous ore.
Cut-off is determined by the market value of
the ore in each unit of rock that is mined
compared to the cost of mining that unit. As
a result, every mining operation has a different
cut-off and criteria for the separation of
waste from ore. Material that is not mineralized
or has had the valuable commodity
extracted from it is disposed of in an appropriate
manner.
The mass excavation of mineralized

material produces waste rock. This material
is commonly drilled, blasted, and hauled to
a permanent storage location and disposed
of in stockpiles. Generally, these stockpiles
or dumps are large and represent complex
geotechnical structures. The heterogeneous
nature of the material stored in waste dumps
and the method of placement favours material
segregation.
This process determines the geotechnical
and hydrogeological behaviour of the
pile. The internal architecture of the pile is
influenced by the material’s grain size,
porosity, hydraulic properties, alteration of
rock forming minerals, and the dynamics associated
with water (e.g. precipitation, evaporation,
runoff, seepage, and water retention).
The handling and storage of mine waste
constitutes a financial cost to the mine operator.
Estimates suggest around 1.5% – 3.5%
of the total operating costs are associated
with mine waste management. A direct, positive
impact on the project cash flow can be
realized from the revenue of a saleable mine
waste product.