Reactive transport modeling is a process-based approach that accounts for advection, diffusion, dispersion and a multitude of biogeochemical reactions. The occurrence of these reactions, by nature, tends to affect the properties of porous media in many ways (Tenthorey and Gerald 2006). If these alteration reactions are significant, then feedback mechanisms could occur that influence the flow of groundwater

Biogeochemical processes are of tremendous importance for determining the fate of many organic and inorganic compounds in the subsurface. Most global elemental cycles involve biogeochemical transformation, and the recycling of carbon and nutrients relies almost exclusively on biogeochemical processes. In particular, the majority of natural organic compounds are biogeochemically reactive, but also a

Nanoporous media consist of homogeneous or heterogeneous porous material in which a significant part of the pore size distribution lies in the nanometer range. Clayey rocks, sediments or soils are natural nanoporous media, and cementitious materials, the most widely used industrial materials in the world, are also nanoporous materials. Nanoporous materials also include compounds present at the interface

A watershed (also drainage basin, river basin, or catchment) is defined as “… the area that topographically appears to contribute all the water that passes through a specified cross section of a stream (the outlet)” (Dingman 2015). In this chapter, I choose to use the term “watershed” as it is a broadly used one; it should be understood more as small watersheds or catchments. Watersheds are the fundamental

Power generation plays an important role in global warming (Audoly et al. 2018) and although the use of nuclear power in the energetic mix can be seen as sustainable (Brook et al. 2014; Knapp and Pevec 2018), nuclear energy is debated in many countries (Meserve 2004; Cici et al. 2012). Over 50 years of nuclear energy and the use of radioactive material in nuclear research and in industrial, medical

Upon injection into a reservoir, CO2 migrates and interacts with the host rock and pore water (Benson et al. 2005, 2012). Supercritical or gaseous CO2 dissolves in the pore aqueous solution as a function of the pressure, temperature, and salinity conditions. This process changes the local chemistry; in that it significantly decreases the pH and promotes geochemical reactions such as the dissolution

This chapter addresses the use of multicomponent reactive transport modeling (MCRTM) in an attempt to understand and quantify the interaction between acid water and rocks or Portland cement (mortar, concrete) during and after the injection of CO2 in deep aquifers (geological CO2 storage) and in the treatment of acid mine drainage (AMD). Anthropogenic acidification of water occurs in the two cases (Gunter

Of the 92 elements naturally present on modern Earth, only 21 are monotopic. The remainder are composed of multiple isotopes, many of which are either stable or decay over such extraordinarily long timescales that they may be considered effectively stable for appropriate applications. These isotopes of a given element are distinguished by the number of neutrons within their nucleus, resulting in subtle

The field of reactive transport lies at the intersection of several disciplines in the Earth and Environmental sciences, including hydrology, geochemistry, biology and geology. The processes in natural and engineered media that are the focus of study of these disciplines take place over a wide range of spatial and temporal scales. Specifically, geological media are characterized by their physical and

The interplay between mixing and reactive processes plays a pivotal role in a range of biogeochemical processes controlling the transport, transformation and turnover of chemical elements (McClain et al. 2003; Dentz et al. 2011; Valocchi et al. 2018). The study of these processes is of primary importance in many scientific disciplines and technical applications, including fluid mechanics, geochemistry

The development of reactive transport soared during the 1990's, driven by the necessity to demonstrate the long-term efficiency of radioactive waste repositories (Bildstein et al. 2019; Claret, 2019; Cama et al. 2019, both this volume). The approach, based on a rigorous description of processes and their coupling, provides a basis of confidence to bridge the gap in time and space between knowledge

Reactive transport in the Earth and Environmental Sciences is at a crossroads today. The discipline has reached a level of maturity well beyond what could be demonstrated even 15 years ago. This is shown now by the successes with which complex and in many cases coupled behavior have been described in a number of natural Earth environments, ranging from corroding storage tanks leaking radioactive Cs

Fractures are ubiquitous and important features in the Earth subsurface (Berkowitz 2002; Pyrak-Nolte et al. 2015). They are created as a result of rock failure when the critical stress (i.e., fracture toughness) is exceeded, or in the case of subcritical crack growth, when cracks propagate under stress conditions below fracture toughness, facilitated by chemical reactions (Atkinson 1984). The necessary

Chemical weathering, or the breakdown of rock to form regolith, occurs within an interface between the highly dynamic atmosphere and the comparably quiescent bedrock boundary known as the Critical Zone (Amundson et al. 2007; Anderson et al. 2007). The Critical Zone hosts a complex biosphere that redistributes water and nutrients while injecting carbon into the regolith as gas, dissolved compounds and

The vadose zone (often called the unsaturated zone) is commonly defined as the geologic media spanning from the land surface to the groundwater table of the first unconfined aquifer (Stephens 2018). The vadose zone is known to play a critical role within the biosphere: (1) as a storage medium to supply water to the plants and atmosphere, and (2) as a controlling agent in the transmission of recharging

Soil organic matter (SOM) represents the single largest actively cycling reservoir of terrestrial organic carbon, accounting for more than three times as much carbon as that present in the atmosphere or terrestrial vegetation (Schmidt et al. 2011; Lehmann and Kleber 2015). SOM is vulnerable to decomposition to either CO2 or CH4, which can increase atmospheric greenhouse gas concentrations (GHGs) and

Open system behavior is predicated on a fundamental relationship between the timescale over which mass is transported and the timescale over which it is chemically transformed. This relationship describes the basis for the multidisciplinary field of reactive transport. In the 20 years since publication of RiMG volume 34: Reactive Transport in Porous Media, reactive transport principles have expanded

High temperature gas–solid reactions interactions are ubiquitous in and on the Earth and other planetary bodies (Fig. 1). In these natural systems, gases are elusive. Like a hurricane’s wind that leaves a path of destruction but no trace of wind after the event, the gas that initiated a gas–solid reaction may be conspicuously absent. Because gases effectively escape from geologic systems, gas–solid

It has been 23 years (as we type) since Carroll and Holloway published the “Volatiles in Magmas” MSA volume (Carroll and Holloway 1994). The 1994 volume dealt with how to safely sample high-temperature gases and analytical methods for volatiles in glasses, which included secondary ion mass spectroscopy and vibrational spectroscopy. Since that time, some things have changed, and some have remained the

Gas–solid reactions result in changes in solid structure and composition including the formation of surface layers or thin films (Delmelle et al. 2018, this volume; Henley and Seward 2018, this volume; King et al. 2018, this volume; Palm et al 2018, this volume; Renggli and King 2018, this volume), dissolution-reprecipitation processes resulting in zoning or porosity and mineral replacement (Altree-Williams

Sulfur dioxide (SO2(g)) is an important gas species in most common volcanic settings on Earth including subduction zones (Shinohara 2013). The relative abundances of SO2(g) may vary at a volcano over time with the highest rates of SO2(g) emissions occurring during eruptive degassing and lesser amounts emitted continuously during quiescent degassing, resulting in a large total amount of SO2(g) integrated

Major and trace elements in igneous and metamorphic rocks are commonly used to infer their petrogenesis (e.g., Carmichael et al. 1974; Wilson 1989; Pearce and Parkinson 1993). To date, our understanding of element transport is informed by diffusion data (e.g., Zhang 2010; Spandler and O’Neill 2010) and partitioning measurements that quantify the fractionation of an element between a mineral and a melt

The common manifestation of an explosive volcanic eruption is the emission of a hot mixture of solid fragments and expanding magmatic gases, referred to as the eruption plume, into the atmosphere (Fig. 1, Sparks et al. 1997; Carey and Bursik 2015). Ash (the rock particles less than two millimeters across) usually dominates the plume’s solid load, whereas water vapor followed by CO2 and lesser amounts

Arc volcanoes are most commonly defined in terms of their magmatic and eruptive histories but the sustained flux of high temperature reactive gases through them, at all stages of their eruptive cycles, equally defines them as large scale, gas phase, chemical reactors (Fig. 1). Inside them, reactive mass transfer occurs continuously as magmatic vapor, released from crystallizing silicate melt at lithostatic

Gas–solid reactions on solar system bodies occur in the vicinity of their surfaces and in their interiors where gases are liberated through magma degassing or thermal devolatilization. The reactions are driven by chemical disequilibria created by exogenic (erosion, impacts) and endogenic processes (tectonics, magmatism) that change the composition of gas–solid systems and/or alter temperature and pressure

Despite its importance in geological sciences, our understanding of interactions between gas and condensed phases (comprising solids and liquids) remains clouded by the fact that, often, only indirect evidence remains for their occurrence. This arises from the tendency for the vapor phase to escape from the condensed phase with which it interacts, owing to its much lower density and thus greater volume

Evaporation and condensation of crystalline or amorphous materials at high temperature are the fundamental processes at low pressure in circumstellar environments such as protoplanetary disks and outflows around evolved stars and supernovae, where liquid is basically unstable. Condensation or evaporation of various dust species in a multi-elemental system causes elemental and/or isotopic fractionation

Chemical reactions involving both solid and gas species are pervasive not only in the natural world, but also in engineered systems. Many common, large-scale industrial processes involve chemical reactions and physical phenomena that occur at a gas–solid interface. The industrial scale production of chemical commodities, oil refining, metallurgy, minerals processing, pulp and paper production, food

Throughout the Earth’s crust from magmatic/volcanic to lower temperature hydrothermal environments, low density aqueous fluids play a fundamental role in its chemical evolution. These gas-like fluids contain a periodic table of elements but their molecular chemistry has been little studied. Even the gas-phase molecular chemistry of the solvent itself, steam or low density supercritical water, is poorly

Geochemistry was dominated by thermodynamic theory for much of its first century of existence (Anderson and Crerar 1993; Nordstrum 2006). Interest in high temperature igneous and metamorphic processes combined with the presumption of long time periods that are available for geochemical reactions justified the assumption of equilibrium thermodynamics. Consequently, geochemists were interested in reactants

Gas mixtures play a crucial role in distributing elements between different parts of Earth and planet-forming systems over a range of settings and temperatures. Despite the fundamental role of gases in geochemical cycles and their prevalence both in the crust and the early solar system, we are unaware of any reviews on this topic. This volume arose from an interest in promoting further research into