Mineral-Aqueous Solution Interfaces and Their Impact on the Environment

• Published in: Geochemical perspectives 2012-10, Vol.1, p.483-742
• Main Authors: Brown, Jr, Gordon E., Calas, Georges
• Format: Article
• Language: English
• Subjects: Earth Sciences; Mineralogy; Sciences of the Universe
• ISSN: 2223-7755; 2410-339X; 2224-2759; 2410-3403
• DOI: 10.7185/geochempersp.1.4

This Perspective describes an area of geochemistry that involves minerals, their surfaces, and the interactions of these surfaces with water and the ions and molecules present in water, some of which, like arsenic, are highly toxic to organisms. The importance of these interactions, together with those between microorganisms and mineral surfaces, cannot be overestimated, for they control the composition of our natural environment and mitigate some of the anthropogenic perturbations that are changing our environment in ways that are often unpredictable and sometimes detrimental. Following overviews of our scientific careers to date, including acknowledgments of our former and current students and research collaborators, we highlight some of the scientific contributions of Victor Goldschmidt, Irving Langmuir, Linus Pauling, Konrad Krauskopf, Werner Stumm, and others that led directly or indirectly to the evolution of this field, recalling personal interactions with some of these pioneers. In all fields of science, advances are made when new experimental methods, new characterisation and computational tools, and new theories become available. The field of mineralwater interface geochemistry is no different and has advanced significantly over the past 30-40 years due to enormous changes in molecular-level experimental methods, particularly those involving the extremely intense X-ray sources known as synchrotrons, in digital computers, and in molecular-level theories. We (GB and GC) offer our perspectives on the development of synchrotron radiation sources and their applications to mineral-water interface processes, based on our personal experiences starting in the early days of these major user facilities. We discuss some of these new methods and theories and their applications to mineral-water interface processes through various examples. Because of the complexity of mineral-water interfaces, particularly in natural Earth surface environments, where natural organic matter and microorganisms play very important roles, we adopt a reductionist approach and consider simple model systems of increasing complexity in our quest to understand the chemical processes occurring at these interfaces at the molecular level. We start with a discussion of the acid-base chemistry of metal-oxide surfaces in contact with bulk water and empirical models of the electrical double layer (EDL) that is thought to develop at solid-water interfaces. We then consider experimental and the