Planet Earth is facing numerous environmental problems such as water contamination, global warming, and growing quantities of hazardous and radioactive waste. Environmental Geochemistry utilizes geological and chemical tools for understanding environmental questions. This discipline investigates natural and anthropogenically-induced processes, which involve complex interactions between the solid Earth, water, dissolved inorganic and organic constituents and living organisms. These chemical and physical processes have profound effects on a wide variety of societal problems such as toxic waste, radioactive waste, acid rain and acid mine drainage. There is, therefore, a current need to understand the factors that govern the interactions between rocks and water-based solutions. Such understanding is also required in order to quantify natural processes such as weathering. In the research of my group, we use both laboratory experiments and theoretical modeling in order to explore the fundamental principles behind the mechanisms that control the three main processes of water-rock interactions, (sorption, dissolution and precipitation).
In nature, as well as during anthropogenic activities, there are many environmental factors that govern the thermodynamics and kinetics of water-rock interactions. In the laboratory the situation is somewhat simpler. One can conduct a series of experiments in which one factor is manipulated while all other factors are held constant. The outcome of such experiments is usually a simple rate law describing the effect of the manipulated variable on the rate of dissolution and precipitation reactions. Many such experiments investigating the effect of variables such as temperature, pH, ionic strength, catalysis and inhibition by inorganic and organic compounds and deviation from equilibrium are reported in the geochemical literature. A large effort has been made in recent years, to formulate a general form of the rate law to generalize the simple rate laws. Such general rate laws may be implemented in field studies of natural processes as well as of processes affected by anthropogenic activities.
Studies on weathering and mineral dissolution:
The ultimate goal of this part of my research is to study the full dissolution rate law of minerals at low temperature. The research involved both experimental and pure theoretical studies. In these studies we examined how the dissolution rate is affected by temperature, pH, catalysis and inhibition by organic and inorganic compounds, surface area and degree of saturation. The dissolution kinetics of the following minerals were studied: gibbsite, kaolinite, smectite, plagioclase, k‑feldspar, biotite, zeolite, gypsum and hashemite and muscovite. The theoretical work included postulating mechanistic models for the proton-promoted and hydroxyl-promoted dissolution reaction, for catalysis by organic substances and for inhibition of a dissolution reaction.
Studies on the coupling between dissolution and precipitation:
One important difference between field and laboratory conditions is that weathering product minerals are often intimately associated with the primary minerals in nature. In contrast, in laboratory experiments, the precipitation of product minerals was often avoided by adjusting the chemistry and recirculation rate of the fluid phase. In theoretical papers, we showed that there is a strong coupling between the kinetics of the dissolution of the primary minerals and the precipitation of the secondary minerals. Using literature data, we demonstrated that such strong coupling exists in experiments that were conducted under relatively high temperatures (300°C). Following these theoretical studies, we started to conduct laboratory experiments in order to demonstrate the existence of this predicted coupling under ambient conditions.
As precipitation of secondary minerals, is an inherent part of weathering processes, we are also studying the nucleation kinetics of clay minerals.
Studies on thermodynamics and kinetics of evaporites precipitation:
The major aim of this part of my research is to understand the mechanism of nucleation and crystal growth in general, and under evaporative conditions in particular. As a supersaturated solution evaporates and minerals precipitate, the solution's chemistry, thermodynamic state and precipitation kinetics are altered. During evaporation, the concentrations of the dissolved ions increase, including the concentrations of the dissolved lattice ions and possible catalysts and inhibitors. Precipitation, on the other hand, leads to a decrease in the concentrations of the dissolved lattice ions and may change their respective ratio in the solution. Since most variables that control precipitation kinetics are interrelated and occur simultaneously with evaporation and consequential precipitation, it is presently impossible to differentiate and quantify the relative impact of each variable. Therefore, it is not possible to predict a-priori the overall effect of evaporation and precipitation on precipitation kinetics. During the last decade, my research group conducted hundreds of experiments studying the thermodynamics and kinetics of nucleation and crystal growth from brines under different environmental conditions. Numerous experiments were conducted with Dead-Sea brines and mixture of seawater and Dead Sea brines as part of our attempt to understand the possible implication of the proposed Red Sea – Dead Sea conduit on gypsum precipitation in the Dead Sea. Other experiments were conducted with reject brines from desalinization plant as part of a study on the formation of gypsum scale.
The carbonate system in the Dead Sea:
Aragonite precipitation in the Dead Sea and in its precursor, the last glacial Lake Lisan, is a result of the common ion effect, induced by the mixing of high bicarbonate freshwater runoff with the extremely Ca-rich Dead Sea brine (DSB). This work focuses on the alkalinity and buffer system of the DSB and its mixtures with freshwater in order to assess the fate of carbonates in the modern lake. The outcomes of this research are essential for the evaluation of past limnological/hydrological regimes under which aragonite laminae were deposited in the Holocene and Late Pleistocene, as well as for future modeling of the lake under different hydrological regimes. The basic thermodynamic properties of the brine’s buffer system are derived, and then combined with field and experimental data to yield a comprehensive description of the dynamics of the carbonate and buffer systems of the brine. The study focuses on three major aspects of the buffer system: (1) Precise determination of the pH of the DSB; (2) Determination of the dissociation constants (pK') of the buffer systems; and (3) The annual and long-term dynamics of the carbonate system in the lake and the role of CO2 degassing vs. aragonite precipitation in removing DIC from the lake.
Studying the kinetics of water-rock interaction, under environmental conditions of geological storage of CO2:
While alternative energy sources may be used to reduce CO2 emission, geological storage of CO2 is the only known mean of mitigating the contribution of fossil fuel emissions to global warming. Understanding the whole gamut of processes that will occur as a result of mixing CO2 and brine within the rock is essential for predicting changes with time at such storage sites. We built a new experimental system at the BGU Water-Rock interaction laboratory that will allow study of interactions between CO2, brine and minerals under CO2 supercritical conditions. Due to the high reactivity of the brine-CO2 mixture, most of the parts constructing the system (e.g., valves, pipes and reaction cell) is be made out of titanium alloy. Using the new experimental system, we study the thermodynamics and precipitation kinetics of sulfate-bearing minerals under environmental conditions of geological storage of CO2.
Although my research is of basic nature, some of its outcomes have important practical implications. The following are a few examples of studies that I conducted with my students and colleagues and their implications:
· We studied the rates of the decomposition of organic contaminants under the Ramat Hovav Industrial Zone. The results of this study imply that high concentrations of contaminant would persist in the aquifer for long periods even after eliminating all of its sources.
· Our studies of the rates of smectite dissolution are used in planning of radioactive waste storage facilities.
· We studied the sources of salinity in the ground-water of the Nubian Sandstone Aquifer (Negev, Israel). Understanding the mechanism of salinization is crucial in planning potential usage of this large aquifer.
· In cooperation with colleagues from the US, Jordan and the Palestinian Authority, we are currently studying the sources of naturally occurring radioactive material in the ground-water of some critical drinking-water aquifers in the Middle East.
· Israel and Jordan announced that they plan to build the “Peace Conduit”, a pipeline connecting the Dead Sea and the Red Sea, in order to controll the decline in Dead Sea water level and to desalinate seawater for distribution to Jordan. One of the critical processes that would be caused by such mixing, and that might affect the chemical composition of the Dead Sea as well as physical parameters (e.g., rate of evaporation) is gypsum precipitation. The results of our field and laboratory experiments would be incorporated in a model that would help understand the possible implications of this project.
Over the years, my research is based on collaborations with many colleagues, students and research groups in Israel and abroad. A partial list includes: J. Cama, X. Querol and C. Ayora (Institut de Ciències de la Terra, Barcelona); V. Metz, D. Bosbach and H. Pieper (Institut für Nukleare Entsorgung, Forschungszentrum Karlsruhe, Germany); Y. Erel, G. Anselmi and I. Bilkis (Hebrew University, Israel); J.D. Blum, L.M. Walter and T. Huston (University of Michigan, USA); A. Vengosh (Duke University, USA); Jose Luis Mogollon (INTEVEP, Venezuela); A. C. Lasaga (Yale University, USA); A. Luttge (Rice University); Peng Lu, Zuoping Zheng, and Chen Zhu (Indiana University, USA), Y. Zeiri (Nuclear Research Center Negev, Israel); S. Zmora-Nahum (Mekorot Israel National Water Co.); I. Gavrieli, Y. Harlavan, Y Yechieli and N. Lanski (Geological Survey of Israel), D. Markel (Water Commission, Israel); I. Bar Ilan (MIGAL, Israel), D. Meyerstein, A. Sivan, S. Feinstein, E. Adar, Y. Oren, Y Volkman, N. Weisbrod, S. Ezra (BGU).
