Using thermal imaging to prevent and forecast particulate emissions from mine tailings - Research Outreach
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Josée Maurais
E: Josee.Maurais@USherbrooke.ca T: +1 819 674 6373 T: +1 819 821 8000 ext 63424
Using thermal imaging to prevent and forecast
particulate emissions from mine tailings
Detail Research Objectives
Département de chimie Josée Maurais and her team examine the drying kinetics of bauxite
Université de Sherbrooke residues to improve forecasting of fugitive dust emissions.
Sherbrooke, J1K 2R1
Canada
Bio
References
Josée Maurais studied chemistry at the Université de Sherbrooke Maurais, J., Beaumont, E., Bourret, J., Dauphinais, E., Bouchard,
(UdeS), where she completed her bachelor’s degree in 2017 N.-A., and Ayotte, P. (2020). A thermal imaging methodology to study
and her master’s degree in physical chemistry in 2019 on drying evaporation kinetics in mine tailings. Environ. Sci.: Water Res. Technol.,
kinetics in mining residues. She is currently a doctoral student
6, 1456–1464. Available at: https://doi.org/10.1039/D0EW00104J
in atmospheric chemistry at UdeS in collaboration with Seoul
National University in the Republic of Korea and the Institute
of Low Temperature Science in Japan. Her research focuses on
the study of the kinetics and mechanisms of heterogeneous
Personal Response
reactions of various atmospheric pollutants at the ice interface. What inspired you to conduct this research?
Maurais is involved in several activities for the promotion of Snow albedo feedback is a process by which dust
science and next-generation researchers, in particular through particles decrease snow albedo which, in turn, enhances snow
the organisation of an Undergraduate Chemistry Colloquium metamorphism, resulting in further decrease in its albedo. This
as director (2017) and through her participation in the popular process has major implications on radiative transfer properties
science TV show GÉNIAL! She also contributes to various in an evolving climate, as well as glacier dynamics and melting.
governmental and academic governance instances whose goals Understanding the effect of fugitive dust emissions from bauxite
are to identify strategies to make funding for graduate studies residues can offer environmental researchers a convenient case
more accessible, promote excellence of student researchers, to further our understanding of snow albedo feedback.
and take part in efforts for the outreach and promotion of
student research. What are you looking to study next?
Fugitive dust emissions can also emanate from frozen bauxite
Funding
residues during winter. Their impacts on neighbouring communities
• Ministère de l’Énergie et des Ressources Naturelles (MERN) du
is exacerbated when deposition occurs over a fresh snow cover.
Québec
These episodes are much more unpredictable as the underlying
• Le Fonds de recherche du Québec — Nature et technologies
mechanisms and rates for water transport within frozen mine
(FRQNT)
tailings are mostly unknown. As evaporation rates from mine
• Le Conseil de la Recherche en Sciences Naturelles et en Génie
tailings are expected to be strongly suppressed during winter as
(CRSNG) du Canada
capillary flow is mostly ineffective when water solidifies in frozen,
• Le Centre Québécois de Recherche et de Développement de
wet bauxite residues, the risks of fugitive dust emissions can be
l’Aluminium (CQRDA)
strongly enhanced as a result of ice sublimation in the dry and
• Le Ministère de l’Économie et de l’Innovation (MÉI) du Québec
• Rio Tinto-Alcan cold conditions typical of winter in Boreal and Polar regions.
Collaborators
• Nicholas-Alexandre Bouchard
• Simon Gaboury and Jonathan Bernier (Rio Tinto-Alcan)
• Étienne Morin (Vision Météo)
Physical Sciences︱Josée Maurais
Using thermal imaging
Josée Maurais used thermal imaging to monitor a bauxite
residue storage area.
to prevent and forecast
particulate emissions
from mine tailings water and air streams and harm the need for efficiency of evaporation can be influential on our ability to
aquatic life. Monitoring the conditions kinetics monitoring, accuracy on the control the fugitive dust emissions
T
Fugitive dust emissions from he aluminium mining and refining when fugitive dust emissions occur of mine tailings, especially their surface monitoring of the surface layer, ability from mine tailing, helping solve a big
dry mine tailings surfaces is business provides valuable from mine tailing surfaces as they dry. drying state and rates, can improve for in situ application, and ease of use environmental issue regarding the
an environmental concern aluminium metal and alumina Indeed, exposed surface layers dry understanding on how they evolve as a for routine, on-site risk assessments. mining industry.
that undermines the mining from bauxite ores in various locations much more rapidly than the deeper function of environmental parameters Thermal imaging was suggested as
industry’s social acceptability. worldwide. Recent incidents at mine layers, thereby increasing the risks of and meteorological conditions, an excellent candidate, covering all THERMAL IMAGING TO
Aluminium refining waste tailing storage facilities exposed the particulate matter emissions. Wind the physico-chemical and surface these requirements, and providing MONITOR WATER EVAPORATION
material management involves environmental challenges facing red erosion causes dispersion and saltation properties of mine tailings, as well as information to improve understanding The principle behind thermal imaging
intensive mud farming activities mud management. Mine tailings refer of particles that become airborne. their thermal history and hygroscopy. of water adsorption on mineral is based on the fact that all objects
intended to accelerate to the leftovers after the valuable Fugitive dust scattering events can surfaces, water evaporation kinetics and emit infrared radiation. Depending
drying prior to the residue’s fractions have been extracted from the indeed be triggered by updrafts and/ MINE TAILING evaporative fluxes, and the influence on the morphology, structure and
permanent storage and site rock. Following gibbsite extraction by or blowing winds conditions when they MONITORING STRATEGIES of environmental factors on them. chemical composition of the object,
remediation. Throughout the hydrothermal Bayer process, waste interact with dry mine tailings surfaces Monitoring of fugitive dust emissions Information on all these parameters the infrared light it radiates can vary;
this process surface products from bauxite ores, composed at storage facilities. The meteorological from mine tailings can be done via
evaporation occurs much
faster, requiring continuous
of crushed rock and solid particles,
mostly iron oxides, are suspended in
conditions and surface moisture
content of mine tailings that make
several available methods, mostly
focusing on water evaporation kinetics Monitoring the conditions of mine
tailings can improve understanding
and in-situ monitoring of mine water effluents. The so-called red mud them prone to cause particulate matter and evaporative fluxes. By ‘looking’ at
tailings’ drying state and
must be left to dry over vast open to be dispersed over neighbouring the rate with which water evaporates
rate to prevent fugitive dust
emissions. Josée Maurais from
expanses prior to site remediation and communities as well as the from the mine tailing surface, on how they evolve as a function
of environmental parameters and
restoration. This is achieved through environment are often poorly known researchers try to predict the impact
the Université de Sherbrooke,
mud farming treatments of mine and difficult to predict. In addition to evaporation and tailing dryness will
Canada, developed a
methodology using thermal tailings performed by heavy machinery
at storage facilities; these are costly
contamination by particulate matter,
acute health and environmental
have on the risk of dust emissions.
Mine tailing monitoring can been
meteorological conditions.
imaging to monitor and
quantify evaporation rates, operations that can last for up to concerns may also result from the done using various techniques
allowing the underlying several years. dispersion of heavy metals or other such as reflectometry (measuring however, given appropriate calibration
mechanisms and their kinetics toxic pollutants that can be carried by the reflection of wet surfaces), and validation, the thermal irradiance
to be elucidated. What many people are not aware of fugitive particulate matter emissions. permittivity and ground-penetrating intensity and spectrum can also reveal
are the environmental issues that arise These could potentially contaminate measurements, electrical conductivity, its temperature. This non-invasive
and visual inspection. method uses a specialised camera
and relevant software for image
However, these methods cannot analysis. When applied to mine tailing
be easily applied for continuous evaporation monitoring, thermal
field monitoring, and cannot easily imaging can indicate differences
differentiate between the surface layer in surface temperature caused by
(which is the one of importance here, evaporative cooling, as, easily put, the
cesar loayza acero/Shutterstock.com
as it is responsible for the formation infrared radiation emanating from a
of dust upon evaporation of the dry parcel of the tailing will reveal that
water that holds dust particles to the it is hotter than that radiating from the
ground by capillary forces arising from cooler, wet parcels.
its surface tension) and the bulk of A thermal imaging camera renders infrared
the mine tailing. Hence, a different radiation as visible light. Based on this idea, doctoral student
method had to be developed to cover Josée Maurais and her colleagues from
researchoutreach.org researchoutreach.org
the Université de Sherbrooke in Canada Based on known information such on the thickness of the layer examined
used thermal imaging to monitor as the examined sample thickness, as well as on the ambient relative
bauxite mine tailings and develop the initial water content, the material humidity. Past this initial stage, the
understanding on the water vapour structure of bauxite residues and evaporation regime changes, with
diffusion and capillary flow within mine their ability to retain water in their temperatures rising (as they were
tailings, as well as on water adsorption pores, their research highlighted the lowered during the initial stage, as
on mineral surfaces. In the team’s most main features that control the drying significant cooling results from rapid
recent publication, “A thermal imaging kinetics of the surface layer of the evaporation) until equilibrium between
methodology to study evaporation tailing. Transforming data from raw the bulk and the surface layer of the
kinetics in mine tailings”, Maurais collected thermal images to surface sample and the ambient air is reached.
revealed a By this point,
simple, portable,
non-invasive
Maurais revealed a simple, portable, non- water transport
from the sample
methodology invasive methodology based on thermal bulk to the surface
imaging to study water evaporation
based on is much slower,
thermal imaging with temperature
to study water
evaporation
kinetics in mine tailings. gradients
approaching zero
kinetics in mine as evaporation
tailings, which could assist with the temperatures, Maurais was able to slows down significantly when water
forecast of fugitive dust emissions, calculate heat and evaporative fluxes, transport become strongly inhibited
based on a better understanding of the and, given structural information, by vapour diffusion through the dry
tailing’s surface drying state. she was able to identify water superficial layers.
WATER EVAPORATION KINETICS
transport mechanisms.
Based on the thermal imaging data, the
Pools of water
OF THE TAILING SURFACE LAYER The publication indicates that the transition between the first and second
Maurais and her colleagues studied initially dominant mechanism is capillary stages of mine tailing evaporation Thermal imaging can indicate differences in surface temperature caused by evaporative cooling. The infrared radiation emanating from a dry parcel of the
the temperature gradients observed in flow (flow through very narrow pores, was clear. Once the second stage is tailing will reveal that it is hotter than that radiating from the cooler, wet parcels (the pools of water).
mine tailings under given environmental passages of hair-like thickness), with completed, the temperature of the
conditions through thermal imaging. evaporation rates depending strongly bulk sample is almost equal to the ambient temperature, and the water how water molecules painstakingly could result in an increase in the
content of the sample is equilibrated find their way, from the deeper layers tortuosity of the pore structure by
with the atmospheric water content, to the surface of the mine tailings, obstructing the smaller pores, thereby
indicating that evaporation is no longer through a very inefficient random walk further hindering water diffusion from
taking place, as the drive for it (water process through the tortuosity of their the bulk to the surface. All these
content differences, temperature interconnected porous microstructure. phenomena may thus contribute to
gradients) does not exist anymore. In Based on experimental work, Maurais various extents to lowering the diffusion
an effort to quantify how much water found that the effective diffusion coefficients displayed by water vapour
was evaporated from the mine tailing, coefficient for water through bauxite through the interconnected pore
Maurais worked backwards, measuring residues decreases with increasing structure of bauxite residues.
the uptake of water from dry bauxite relative humidity of the external
samples under the same environmental ambient air. The effective diffusion Overall, what Maurais showcased
conditions used during evaporation. coefficients were also observed to be with her work was that using thermal
This process is called an “adsorption considerably smaller than expected imaging, an easy, portable, and
isotherm”, as under standardised for gas phase diffusion. These small industrially relevant method, to
temperature and humidity, water diffusion coefficients were attributed in monitor water evaporation kinetics
adsorbed (stuck) on a specified sample parts to the morphology and chemical and evaporative fluxes of mine tailings
is quantified at the point where there is composition of the bauxite residues, allowed for improved understanding
no more water able to be adsorbed on which allowed water molecules to on the evaporation mechanisms and
the porous structure (equilibrium). strongly adsorb onto its surface. rates. This knowledge, combined with
Another potential contribution was information on the structure of bauxite
EFFECTIVE DIFFUSION invoked: diffusive transport through the residues, led to explanations for the
COEFFICIENT IN POROUS MEDIA narrow and tortuous interconnected observed behaviour, and the ability
Using the isotherms to quantify water pore structure may hinder diffusive to improve waste management of
content in mine tailings at equilibrium, transport of water vapour even further. mining facilities. Despite the limitation
Maurais went on to characterise the Finally, the decreasing effective of thermal imaging to only provide
evaporation kinetics by defining diffusion coefficient with increasing average evaporation fluxes rather
the effective diffusion coefficient of relative humidity of ambient air meant than finer details of the sample area,
water vapour in bauxite residues. that, when there was more water this technique can be a great start
The interpretation of an effective vapour available on the ambient, for continuous field monitoring and
Snapshots from a time series showing thermal images of evaporating wet bauxite residue. diffusion coefficient should reveal surface side, capillary condensation support risk assessment efforts.
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