Georges Calas, Author at Elements Magazine

Improving Mitigation of the Long-Term Legacy of Mining Activities: Nano- and Molecular-Level Concepts and Methods

Mining activities over several millennia have resulted in a legacy of environmental contamination that must be mitigated to minimize ecosystem damage and human health impacts. Designing effective remediation strategies for mining and processing wastes requires knowledge of nano- and molecular-scale speciation of contaminants. Here, we discuss how modern nano- and molecular-level concepts and methods can be used to improve risk assessment and future management of contaminants that result from mining activities, and we illustrate this approach using relevant case studies.

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Mineral Resources and Sustainable Development

Mineral resources have been used for millennia and are a key to society’s development. With the growing importance of new technologies and the energy revolution, questions have arisen regarding the future availability of resources of metals and industrial minerals. As discovering large high-grade deposits has become increasingly rare, the concept of “sustainable development” will become viewed as essential to extract metals/minerals from new low-grade deposits. In addition to economic considerations, it is essential to reconcile mining activity with environmental protection and to allay the concerns of local populations. This issue of Elements highlights the progressive movement towards an active environmental and societal strategy for sustainably harnessing mineral resources.

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Environmental Mineralogy: New Challenges, New Materials

Societal and Economic Impacts of Geochemistry, Thematic Articles / Georges Calas

The close links between mineralogy and materials science are leading to major developments in how society deals more effectively with energy and environmental challenges. The fast expanding field of “environmental mineralogy” helps mitigate major environmental issues related to the impact of anthropic activities on the global ecosystem. Focusing on energy related materials and environmental cleanup, this article shows how minerals inspire us to design new materials for advanced technologies needed for energy production, managing contaminated areas, and disposing of nuclear waste. We illustrate the environmental importance of nanomaterials, non and poorly crystalline phases, and the interactions between minerals and ubiquitous microbial activity.

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Kaolin-Group Minerals: From Hydrogen-Bonded Layers to Environmental Recorders

Kaolin, Thematic Articles / Etienne Balan

Kaolin-group minerals typically form as a result of hydrothermal alteration and/or weathering processes. They occur in environments as diverse as tropical soils, continental sedimentary deposits, and altered crustal rocks. They have also been detected on the surface of Mars. Given their prevalence, they have attracted the attention of researchers in materials chemistry, environmental geochemistry, and high-pressure mineral physics. Their structure and related properties have been studied for about a century, and these studies reflect advances in experimental techniques, modeling approaches, and concepts in mineralogy. Among key features of their structure are the predominance of 2-D stacking defects and the peculiar role of H-bonding in the control of their polytypism.

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The Structure of Silicate Glasses and Melts

Glasses and Melts: Linking Geochemistry and Materials Science, Thematic Articles / Grant S. Henderson

Much progress has been made in elucidating the complex structures of silicate glasses and melts. X-ray and neutron scattering, spectroscopy, and theoretical calculations now provide a reasonably clear picture of many aspects of the short-range structure of glasses (which approximates the melt structure at the glass transition temperature). Critical effects of redox conditions and volatiles on structure have been clarified. Qualitatively, links between structure and properties such as molar volume, entropy, cation partitioning, and viscosity have been established, but quantitative connections remain challenging. Effects of temperature and pressure on structure have been the subject of much recent work.

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Glasses and Melts: Linking Geochemistry and Materials Science

Glasses and Melts: Linking Geochemistry and Materials Science, Thematic Articles / Georges Calas

Silicate melts are major components of magmatic activity and of its most spectacular expression, volcanic eruptions. The “hidden part” is even more fascinating, as silicate melts are directly involved in matter and heat transfer within the Earth and planets. Silicate glasses, often investigated as a frozen picture of their molten counterparts, are also materials of major importance in technology. Despite the difficulties in rationalizing physical and chemical properties of glasses and melts, due to an incomplete knowledge of their structure, major progress has been made recently in synthetic and natural systems. This issue of Elements reviews the properties of silicate glasses and melts from the molecular to the field scale. It includes insights into their technological applications and describes some recent advances this fast-evolving field.

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Arsenic in Soils, Mine Tailings, and Former Industrial Sites

Arsenic, Thematic Articles / Guillaume Morin

Much progress has recently been made on the relation between the crystal chemistry of arsenic and its speciation and distribution at the Earth’s surface. The investigation of As-impacted soils and acid mine drainages, using synchrotron-based techniques, shows the importance of As adsorption on, or coprecipitation with, hydrous ferric oxides in delaying the long-term impact of As on the biosphere. Arsenic mobility often depends on bacterial activity, with accompanying major seasonal modifications of As speciation, even at extreme As concentrations. Remediation technologies use geochemical affinities between arsenic and specific low-temperature phases to reduce the bioavailability of arsenic.

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Scientific Advances Made Possible by User Facilities

Thematic Articles, User Research Facilities in the Earth Sciences / Gordon E. Brown Jr.

National scientific user facilities are becoming increasingly available to many different scientific communities in a number of countries. There is a growing use of these facilities by Earth and environmental scien- tists to study a broad range of materials and processes under realistic P–T and environmental conditions at unprecedented levels of energy and spatial resolution and elemental and isotopic sensitivity. The results of these studies are providing new insights into biogeochemical processes operating at Earth’s surface as well as petrological, geochemical, and geophysical processes in Earth’s interior. The availability of national user facilities is changing scien- tific approaches and is leading to multidisciplinary studies that were not possible a decade ago.

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User Facilities around the World

Thematic Articles, User Research Facilities in the Earth Sciences / Gordon E. Brown Jr.

National and international communities of scientists from a variety of disciplines have been successful in convincing a growing number of countries to construct major user facilities that collectively serve these communities. These user facilities make possible experimental studies that cannot be done in individual investigator laboratories. In addition, they have created a new style of research, in which scientists working in shared facilities conduct studies that benefit from a merging of ideas and techniques from different disciplines. Earth science users of these facilities are growing in number and are benefiting greatly from the multidisciplinary interactions such facilities stimulate and from the unique experimental capabilities they provide.

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Author name: Gordon E. Brown Jr.