Developing analytical methods for complex mixtures

Chemically complex mixtures, such as crude oil and its derivatives, biofuels and biomaterials, are prevalent in the environment. Their sources and environmental fates are often poorly understood, owing to the complexity in their composition. Our research group focuses on developing analytical techniques to characterize these environmental mixtures. We develop techniques to speciate organic compounds in atmospheric aerosol by carbon number, branching and cyclization on a laboratory scale. Through understanding the molecular characteristics of these mixtures, we can better constrain their sources, properties, and environmental fates.

Chemical characterization of semivolatile and particle-phase emissions

Organic aerosol is a major fraction of particulate matter, and has important effects on global climate change and local air quality. It can be directly emitted from sources (primary) or formed from oxidation of volatile or semivolatile emissions (secondary). One major focus of the research group is speciating in urban emissions of semivolatile and particle-phase compounds. Specific compounds unique to various sources are used to estimate the overall contribution to atmospheric organic aerosol.

Atmospheric oxidation chemistry of organic compounds

Most organic aerosol is secondary, formed from atmospheric oxidation of gas-phase and semivolatile emissions. We simulate the oxidation of primarily emitted compounds to form secondary products in a laboratory reactor. This allows us to control important environmental variables, such as temperature, oxidants and humidity. With detailed knowledge of the composition, we can probe the effect of molecular structures on aerosol formation mechanisms. The oxidative capacity of laboratory-generated aerosol is also linked to the effect of particulate matter on human health.

Aqueous and Environmental Process Engineering

The mining and metals industry is facing the need to develop novel technology that addresses the requirements for sustainability in the extraction and processing of natural mineral resources. The Aqueous Process Engineering and Chemistry (APEC) group is providing solutions in the processing of complex mineral resources by studying the fundamentals of aqueous process chemistry and engineering to recover and produce metals or metallic products by hydrometallurgical routes. The research focuses on developing novel chemical processing ideas to:

• Treat increasingly complex mineral deposits with low metal content including wastes, for the recovery and separation of base, precious and critical rare earth metals;
• Reduce the environmental impact (on water, land, and air), as well as minimize the use of energy and chemicals including water;

Specific project examples are:

1. Water purification by forward osmosis: Removal of soluble salts by lower energy consuming technologies compared to reverse osmosis and evaporation. Introduces low-cost bleed of salts and process water recycling to minimise fresh water intakes.
2. Bio-hydrometallurgy of sulphidic wastes for base metal recovery, and remediation:Bioleaching of sulphidic wastes to recover pay metals and discharge the acid-mine-drainage toxicity of tailings.
3. Aqueous chemistry and recovery of rare earth elements: Ion exchange leaching of ionic clays and production of a mixed oxide product by novel process configurations.
4. Recovery of metals by molten salt hydrate systems: Development of new chemistry that uses very little water and moderate energy input to extract metals from raw materials.
5. Pressure oxidation of metallurgical wastes (slags) for base metal recovery and remediation: Total remediation and cleanup of waste slags with simultaneous recovery of base metals by POX technology.
6. Development of sensors for acid and redox monitoring in aqueous streams at high temperatures: In situ monitoring by robust sensors in a variety of slurry streams in temperatures ranging from room to those in autoclaves
7. Chemical modeling of complex aqueous electrolyte solutions: Development of dedicated databases for modeling the chemistry (i.e., speciation, solubility, vapor-liquid equilibria) of salts and other compounds in complex multicomponent process solutions within very wide temperature ranges.

Surface waters regularly receive all kinds of contaminants with the potential to threaten ecosystem and human health. Some of these chemicals are “emerging” organic contaminants for which limited information is available, such as pharmaceuticals, compounds in personal care products, and current use pesticides. Typical loads of these anthropogenic chemicals in urban, industrial, and agricultural areas are presented in the attached figure.

To protect water quality from adverse effects due to these and other emerging contaminants, the research of our group is driven by three main objectives:

(1) to track the behavior of specific emerging contaminants in surface waters;
(2) to develop and evaluate novel cost-effective water treatment technologies based on ecological engineering principles;
(3) to develop a new application for stable isotope techniques to quantify trace levels of emerging contaminants in surface waters.

This information is vital for the development of appropriate policies and engineering solutions for use, disposal, and sustainable removal of these chemicals.

 

Sherwood Lollar’s pioneering research on the geochemistry of deep crustal fluids has focused on fracture fluids 1-3 km deep in Precambrian Shield rocks across Canada, Fennoscandian and South Africa. Continuing work in this area seeks to determine the extent and volume of this isolated hydrosphere; to determine the relationship of the free flowing fracture waters to trapped fluid inclusions; and to determine the habitability of this exotic realm of the deep subsurface and its implications for the search for extinct or extant life on Mars and elsewhere.

Dr. Sherwood Lollar’s research in groundwater quality and remediation – specifically investigations of degradation of toxic organic compounds using stable isotopes – led the field of stable carbon isotope analysis in environmental geochemistry of organic contaminants in groundwater.  Her research established the scientific principles involved in using compound specific stable carbon isotope signatures, rather than just concentration levels of contaminants, to determine the source of contaminants in groundwater and to track their movement, fate, and particularly, the effectiveness of proposed environmental clean-up strategies. A second important aspect and corollary of these results is that the degree of fractionation observed during transformation of a compound is controlled by the specifics of the reaction mechanisms, or which bonds are broken.  This second important feature of Sherwood Lollar’s research was explored in a series of impactful publications that demonstrated the ability to use CSIA to identify different reaction mechanisms at work at field sites. In situ degradation remediation schemes involving both biotic and abiotic processes are a major focus of R&D on site remediation for organic contaminants.