8 research outputs found
Accelerated Carbonation of Brucite in Mine Tailings for Carbon Sequestration
No full textAtmospheric CO2 is sequestered within ultramafic mine
tailings via carbonation of Mg-bearing minerals. The rate of carbon
sequestration at some mine sites appears to be limited by the rate
of CO2 supply. If carbonation of bulk tailings were accelerated,
large mines may have the capacity to sequester millions of tonnes
of CO2 annually, offsetting mine emissions. The effect
of supplying elevated partial pressures of CO2 (pCO2) at 1 atm total pressure, on the carbonation
rate of brucite [Mg(OH)2], a tailings mineral, was investigated
experimentally with conditions emulating those at Mount Keith Nickel
Mine (MKM), Western Australia. Brucite was carbonated to form nesquehonite
[MgCO3·3H2O] at a rate that increased linearly
with pCO2. Geochemical modeling indicated
that HCO3– promoted dissolution accelerated
brucite carbonation. Isotopic and aqueous chemistry data indicated
that equilibrium between CO2 in the gas and aqueous phases
was not attained during carbonation, yet nesquehonite precipitation
occurred at equilibrium. This implies CO2 uptake into solution
remains rate-limiting for brucite carbonation at elevated pCO2, providing potential for further acceleration.
Accelerated brucite carbonation at MKM offers the potential to offset
annual mine emissions by ∼22–57%. Recognition of mechanisms
for brucite carbonation will guide ongoing work to accelerate Mg-silicate
carbonation in tailings
Bioleaching of Ultramafic Tailings by <i>Acidithiobacillus</i> spp. for CO<sub>2</sub> Sequestration
No full textBioleaching experiments using various acid-generating substances, i.e., metal sulfides and elemental sulfur, were conducted to demonstrate the accelerated dissolution of chrysotile tailings collected from an asbestos mine near Clinton Creek, Yukon, Canada. Columns, possessing an acid-generating substance colonized with Acidithiobacillus sp., produced leachates with magnesium concentrations that were an order of magnitude greater than mine site waters or control column leachates. In addition, chrysotile tailings were efficient at neutralizing acidity, which resulted in the immobilization of metals (Fe, Cu, Zn) associated with the metal sulfide mine tailings that were used to generate acid. This suggests that tailings from acid mine drainage environments may be utilized to enhance chrysotile dissolution without polluting “downstream” ecosystems. These results demonstrate that the addition of an acid-generating substance in conjunction with a microbial catalyst can significantly enhance the release of magnesium ions, which are then available for the precipitation of carbonate minerals. This process, as part of a carbon dioxide sequestration program, has implications for reducing net greenhouse gas emissions in the mining industry
A Greenhouse-Scale Photosynthetic Microbial Bioreactor for Carbon Sequestration in Magnesium Carbonate Minerals
No full textA cyanobacteria dominated consortium
collected from an alkaline
wetland located near Atlin, British Columbia, Canada accelerated the
precipitation of platy hydromagnesite [Mg5(CO3)4(OH)2·4H2O] in a linear flow-through
experimental model wetland. The concentration of magnesium decreased
rapidly within 2 m of the inflow point of the 10-m-long (∼1.5
m2) bioreactor. The change in water chemistry was monitored
over two months along the length of the channel. Carbonate mineralization
was associated with extra-cellular polymeric substances in the nutrient-rich
upstream portion of the bioreactor, while the lower part of the system,
which lacked essential nutrients, did not exhibit any hydromagnesite
precipitation. A mass balance calculation using the water chemistry
data produced a carbon sequestration rate of 33.34 t of C/ha per year.
Amendment of the nutrient deficiency would intuitively allow for increased
carbonation activity. Optimization of this process will have application
as a sustainable mining practice by mediating magnesium carbonate
precipitation in ultramafic mine tailings storage facilities
Accelerating Mineral Carbonation Using Carbonic Anhydrase
No full textCarbonic anhydrase (CA) enzymes have
gained considerable attention
for their potential use in carbon dioxide (CO2) capture
technologies because they are able to catalyze rapidly the interconversion
of aqueous CO2 and bicarbonate. However, there are challenges
for widespread implementation including the need to develop mineralization
process routes for permanent carbon storage. Mineral carbonation of
highly reactive feedstocks may be limited by the supply rate of CO2. This rate limitation can be directly addressed by incorporating
enzyme-catalyzed CO2 hydration. This study examined the
effects of bovine carbonic anhydrase (BCA) and CO2-rich
gas streams on the carbonation rate of brucite [Mg(OH)2], a highly reactive mineral. Alkaline brucite slurries were amended
with BCA and supplied with 10% CO2 gas while aqueous chemistry
and solids were monitored throughout the experiments (hours to days).
In comparison to controls, brucite carbonation using BCA was accelerated
by up to 240%. Nesquehonite [MgCO3·3H2O]
precipitation limited the accumulation of hydrated CO2 species,
apparently preventing BCA from catalyzing the dehydration reaction.
Geochemical models reproduce observed reaction progress in all experiments,
revealing a linear correlation between CO2 uptake and carbonation
rate. Data demonstrates that carbonation in BCA-amended reactors remained
limited by CO2 supply, implying further acceleration is
possible
Microbially Mediated Mineral Carbonation: Roles of Phototrophy and Heterotrophy
No full textUltramafic mine tailings from the Diavik Diamond Mine, Canada and
the Mount Keith Nickel Mine, Western Australia are valuable feedstocks
for sequestering CO2 via mineral carbonation. In microcosm
experiments, tailings were leached using various dilute acids to produce
subsaline solutions at circumneutral pH that were inoculated with
a phototrophic consortium that is able to induce carbonate precipitation.
Geochemical modeling of the experimental solutions indicates that
up to 2.5% and 16.7% of the annual emissions for Diavik and Mount
Keith mines, respectively, could be sequestered as carbonate minerals
and phototrophic biomass. CO2 sequestration rates are mainly
limited by cation availability and the uptake of CO2. Abundant
carbonate mineral precipitation occurred when heterotrophic oxidation
of acetate acted as an alternative pathway for CO2 delivery.
These experiments highlight the importance of heterotrophy in producing
sufficient DIC concentrations while phototrophy causes alkalinization
of waters and produces biomass (fatty acids = 7.6 wt.%), a potential
feedstock for biofuel production. Tailings storage facilities could
be redesigned to promote CO2 sequestration by directing
leachate waters from tailings piles into specially designed ponds
where carbonate precipitation would be mediated by both chemical and
biological processes, thereby storing carbon in stable carbonate minerals
and potentially valuable biomass
Subarctic Weathering of Mineral Wastes Provides a Sink for Atmospheric CO<sub>2</sub>
No full textThe mineral waste from some mines has the capacity to trap and
store CO2 within secondary carbonate minerals via the process
of silicate weathering. Nesquehonite [MgCO3·3H2O] forms by weathering of Mg-silicate minerals in kimberlitic
mine tailings at the Diavik Diamond Mine, Northwest Territories, Canada.
Less abundant Na- and Ca-carbonate minerals precipitate from sewage
treatment effluent deposited in the tailings storage facility. Radiocarbon
and stable carbon and oxygen isotopes are used to assess the ability
of mine tailings to trap and store modern CO2 within these
minerals in the arid, subarctic climate at Diavik. Stable isotopic
data cannot always uniquely identify the source of carbon stored within
minerals in this setting; however, radiocarbon isotopic data provide
a reliable quantitative estimate for sequestration of modern carbon.
At least 89% of the carbon trapped within secondary carbonate minerals
at Diavik is derived from a modern source, either by direct uptake
of atmospheric CO2 or indirect uptake though the biosphere.
Silicate weathering at Diavik is trapping 102–114 g C/m2/y within nesquehonite, which corresponds to a 2 orders of
magnitude increase over the background rate of CO2 uptake
predicted from arctic and subarctic river catchment data
Carbon sequestration in biogenic magnesite and other magnesium carbonate minerals
No full textThe stability and longevity of carbonate minerals make them an ideal sink for surplus atmospheric carbon dioxide. Biogenic magnesium carbonate mineral precipitation from the magnesium-rich tailings generated by many mining operations could offset net mining greenhouse gas emissions, while simultaneously giving value to mine waste products. In this investigation, cyanobacteria in a wetland bioreactor enabled the precipitation of magnesite (MgCO ), hydromagnesite [Mg (CO ) (OH) ·4H O], and dypingite [Mg (CO ) (OH) ·5H O] from a synthetic wastewater comparable in chemistry to what is produced by acid leaching of ultramafic mine tailings. These precipitates occurred as micrometer-scale mineral grains and microcrystalline carbonate coatings that entombed filamentous cyanobacteria. This provides the first laboratory demonstration of low temperature, biogenic magnesite precipitation for carbon sequestration purposes. These findings demonstrate the importance of extracellular polymeric substances in microbially enabled carbonate mineral nucleation. Fluid composition was monitored to determine carbon sequestration rates. The results demonstrate that up to 238 t of CO could be stored per hectare of wetland/year if this method of carbon dioxide sequestration was implemented at an ultramafic mine tailing storage facility. The abundance of tailings available for carbonation and the anticipated global implementation of carbon pricing make this method of mineral carbonation worth further investigation
Data_Sheet_1_Cation Exchange in Smectites as a New Approach to Mineral Carbonation.docx
No full textMineral carbonation of alkaline mine residues is a carbon dioxide removal (CDR) strategy that can be employed by the mining industry. Here, we describe the mineralogy and reactivity of processed kimberlites and kimberlite ore from Venetia (South Africa) and Gahcho Kué (Canada) diamond mines, which are smectite-rich (2.3–44.1 wt.%). Whereas, serpentines, olivines, hydrotalcites and brucite have been traditionally used for mineral carbonation, little is known about the reactivity of smectites to CO2. The smectite from both mines is distributed as a fine-matrix and is saponite, Mx/mm+Mg3(AlxSi4−x)O10(OH)2·nH2O, where the layer charge deficiency is balanced by labile, hydrated interlayer cations (Mm+). A positive correlation between cation exchange capacity and saponite content indicates that smectite is the most reactive phase within these ultramafic rocks and that it can be used as a source of labile Mg2+ and Ca2+ for carbonation reactions. Our work shows that smectites provide the fast reactivity of kimberlite to CO2 in the absence of the highly reactive mineral brucite [Mg(OH)2]. It opens up the possibility of using other, previously inaccessible rock types for mineral carbonation including tailings from smectite-rich sediment-hosted metal deposits and oil sands tailings. We present a decision tree for accelerated mineral carbonation at mines based on this revised understanding of mineralogical controls on carbonation potential.</p
