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An advanced-level introduction to aqueous geochemistry, focusing on the behavior of chemical species in various geological systems, including the continental crust, upper mantle, seawater, sediments, oceanic crust, soil, biosphere, hydrothermal systems, and the atmosphere. Topics covered include open vs. Closed systems, species vs. Components, types of chemical reactions, and chemical components in natural waters. The document also discusses concentration units and minerals in equilibrium with natural waters, as well as ph values in the environment. Applications of aqueous geochemistry include understanding the coupling of the lithosphere, hydrosphere, and atmosphere, ore deposit formation, contaminant fate in soil and groundwater, deep-well injection schemes, and acid-mine drainage.
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Advanced Aqueous Geochemistry
Continental Crust
Upper Mantle
Seawater
Sediments
Oceanic Crust
Soil
Biosphere
Hydrothermal
Weathering
Magmatic/Hydrothermal
Scavenging
Magmatic / Hydrothermal
Atmosphere
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Open Systems can exchange matter with the surroundings. An open system will evolve to steady state. Closed Systems cannot exchange matter and have constant composition. A closed system will evolve to chemical equilibrium. No geochemical system is closed; however we can say a system is approximately closed on a particular time-scale.
The chemical species of a system are the atoms/ molecules/complexes etc. that form in the system. Ca +2^ , HCO 3 -^ , H 2 CO 3 , H+, CO 3 -2^ , H 2 O, OH - The chemical components of a system are the minimum set of chemical species needed to define all the other chemical species in the system: Ca +2^ , H 2 CO 3 , H 2 O, H +
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Complexation : (i) Cu +^ + 2Cl -^ = CuCl 2 - Ion Exchange : Na 2 -Montmorillonite + Ca +2^ (aq) = Ca-Montmorillonite + 2Na +(aq) Surface Complexation : Cu +2^ + 2 >FeOH-0.5^ = (>FeOH) 2 Cu +
Major components : Ca +2^ , Na +, K +^ and Mg + HCO 3 -^ , Cl - , SO 4 - Dissolved Gases : CO 2 (as H 2 CO 3 etc.), O 2 Important trace components : Fe +2^ , Mn+2^ , PO 4 -3^ , N (as NO 3 -^ or NH 4 +^ )
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Molality : moles of species/component per kg of water. Normality : equivalents of species per kg of water (usually based on charge) Molarity : moles of species/component per litre of water ppm : mg of component per kg of water ppb : μg of component per kg of water
Sulphates, Carbonates : Calcite CaCO 3 , Gypsum CaSO 4 .2H 2 O Clay Minerals : Smectites, Kaolinite, Illite, Chlorite Secondary Oxides: Goethite (α-FeOOH), Birnessite (δ-MnO 2 )
Note: primary igneous and metamorphic minerals (except for quartz) will almost never be in equilibrium with an aqueous solution at low P,T.
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