INTEGRATED FIELD, ANALYTICAL, EXPERIMENTAL, AND THEORETICAL APPROACHES IN UNDERSTANDING LARGE, COMPLEX GEOSYSTEMS: A TRIBUTE TO AND THE LEGACY OF DON RIMSTIDT

In a brilliant treatise on the kinetics of silica-water reactions, J. Donald Rimstidt’s first professional publication became one of the more influential geochemical papers ever written. Together with co-author and Penn State Ph.D. advisor Hubert Barnes, this paper explored silica-water interactions and reaction characteristics over a wide range of temperatures, from Earth surface to hydrothermal conditions, and presented a differential rate equation for silica-water reactions from 0 to 300°C together with corresponding equilibrium constants for these reactions with quartz, cristobalite, and amorphous silica. This paper has been referenced nearly 600 times, and perhaps even more remarkably, its citation rate has remained nearly constant for the last 30 years! This shows the astonishing staying power of this publication, achieved by choosing the most common geochemical component in the Earth’s crust (silica), conducting meticulous experiments, deriving a comprehensive theoretical assessment of the system, and presenting numerous examples of wide-ranging applications.

Work like this has inspired our group over the last decade to tackle the complexities of toxic metal geochemistry in the largest civilian contaminated site in the United States, the Clark Fork River Superfund Complex. Due to very large-scale based metal mining in the upper reach and headwaters of the Clark Fork River in western Montana, USA since the 1860’s, tens of thousands of tons of Cu, Zn, As, and Pb have moved well over 500 kilometers down this river basin entrained in bed, hyporheic, and floodplain sediments, and ground- and river water, resulting in 1,600 square kilometers in Superfund designated lands. Our team has established the geochemical behavior of these toxic metals in this vast system using: 1) extensive water and sediment sampling; 2) a large array of sample preparation and analytic methods, particularly TEM and associated techniques; 3) thermodynamic and kinetic considerations; and 4) experimental work designed to simulate bulk, surface/interface, and nanoscale/nanoparticle processes. The metal behavior in this system is driven by the presence of newly discovered crystalline and amorphous nanoparticles, striking heterogeneity, and kinetically influenced system components along with thermodynamic disequilibrium.