GEOCHEMISTRY A - GEOCHEMISTRY B
Learning outcomes of the course unit
Consolidate the base chemistry knowledge, give to the student the competence for the description of the natural systems by the quantitative analysis of the natural geochemical processes and of anthropic meaning.
Course contents summary
General concepts of system and phase, equilibrium state and transformation of a system. Chemical reaction: definition and meaning. Chemical components. Chemical equilibrium: generality, the chimica potential and the condition of equilibrium. Phase equilibrium, chemical reaction equilibrium. Concentrations: mass concentration, molar fraction, molality, molarity. The chemical potential dependence from composition. Fugacity, activity. The standard state. The equilibrium constant, equilibrium constant and chemical potential. Standard free energy of formation. Ionic force and activity coefficients in aqueous solutions. Acids, bases; water dissociation, dependence of KW from T and P. Dissolution-deposition in aqueous solution. CO2 and carbonates. Dissolution of CO2 in fresh water and the influence on pH. Carbonic species in solution as a function of pH. Equilibrium aqueus solution-carbonates (calcite). The calcite-water system. The calcite-water-CO2 system: system open to atmosphere. The role of T and P on the calcite-aqueous solution equilibrium. The role of the ionic force on the calcite solubility. Mixing of water equilibrated at different PCO2 and the influence on the solubility of carbonates. Soil and karst phenomena. Silica phases, silicates, hydroxides. The silica phases-aqueous solution system: aqueous solution concentration of the Si species in equilibrium with the silica phases. The gibbsite-aqueous solution system: aqueous solution concentration of the Al species in equilibrium with gibbsite. The kaolinite-aqueous solution system: aqueous solution concentration of the Al and Si species in equilibrium with kaolinite. Dissolution of the Mg-silicates. The K-feldspar-muscovite-quartz-kaolinite-gibbsite-water system and the chemical evolution of the aqueous solution with the progress of the aqueous solution-mineral interaction. Redox processes in aqueous solution. Redox reactions and redox potential (Eh). Definition and H2O stability. Eh-pH diagrams: solid phase-solution equilibrium. Stability of the Fe-phases (eg: goethite, hematite, magnetite). Stability of the Mn-phases (eg: pirolusite, hausmannite). Eh-pH diagrams: equilibrium of species in solution (isoactivity diagrams). Nitrogen species (N2, NO3-, NO2-, NH4+). Sulphur species (H2S, HS-, HSO4-, SO42-). Environmental importance. Interaction of water and solid phases. Geochemisatry of the waters. Species in solution, colloids and particle suspension. Temperature, pH. Conductivity, Alkalinity. The redox potential and its meaning. Components in solution (eg: Si, Fe, Al, Mn, K, Na, Ca, Mg): origin and speciation. Residence time of a chemical component in a system. Classification of the waters. The diagrams of Piper, Langelier-Ludwig. Oxidation state of the groundwaters. The reduction of nitrates and sulphates by interaction with the rocks of the aquifer. Redox sequences. Oxidation of sulphides and the ambiental impact. Ocean waters. Composition and compositional homogeneity. Continental waters. Composition and compositional heterogeneity. Composition dependence on water-rock interaction. Example: waters from carbonates, from ultramafic rocks, from granitoid rocks.Definition of isotope. Stable isotopes. Isotope fractionation. Isotope ratio and the definition of (delta). The expression of fractionation (the fractionation factor, the enrichment factor, the separation value, their relationships and some exemples). Condensation of the gas. The Rayleigh equation for condensation. Evaporation. Relative humidity. Evaporation and Rayleigh fractionation. Stable isotopes of the waters. Stable isotopes of oxigen and hydrogen. Oceans. Meteoric waters (equation of Craig of meteoric waters, temperature.isotopic ratio relationships, main isotopic variations). Surface waters and groundwaters (isotopes as tracer of the nutrients in the surface and ground waters, water-rock interaction). Other stable isotopes of environmental importance. Carbon, sulphur, nitrogen and strontium isotopes.
Venturelli G (2003) Acque, minerali e ambiente. Pitagora editrice, Bologna
Fornaseri M (1984) Lezioni di Geochimica, Libreria eredi V. Veschi, Roma
Clark I e Fritz P (1997) Environmental Isotopes in Hydrogeology. CRC Press LLC
Fergusson JE (1990) The heavy elements: chemistry, environmental impact and health effects. Pergamon press
Stumm W e Morgan JJ (1996) Acquatic chemistry. Wiley & Sons
ex cathedra teaching
Assessment methods and criteria