Leaching hydrothermal

A commercial process which uses hydrothermal leaching on a large scale is the Bayer process for production of aluminum oxide (see Aluminum compounds). This process is used to extract and precipitate high grade alurninum hydroxide (gibbsite [14762-49-3]) from bauxite [1318-16-7] ore. The hydrothermal process step is the extraction step in which concentrated sodium hydroxide is used to form a soluble sodium aluminate complex ... 

Altenhein, F. K., Lutze, W. Malow, G. 1981. The mechanisms for hydrothermal leaching of glass and glass-ceramic nuclear waste forms. In MOORE, J. G. (ed) Scientific Basis for Nuclear Waste Management III. Plenum Press, New York, USA, 363-370. 

Mai.ow, G. 1982. The mechanisms for hydrothermal leaching of nuclear waste glasses properties and evaluation of surface layers. In Lutze, W. (ed)... 

Deposits of massive cryptocrystalline magnesite occur in serpentized ultra-basic rock that has undergone a hydrothermal leaching of magnesium from the serpentine see reaction (2.5). The hydrothermal solution... 

By hydrothermal leaching of granitic rocks containing uranium and subsequent deposition, veins with uranium contents of several percent can be formed. This is the case in deposits at Joachimsthal in Bohemia, at Port Radium in Canada, and at Chin-golobwe in Zaire (Congo Kinshasa). 

Diluted iodate solution is obtained by hydrothermal vat leaching of caUche ore during nitrate recovery. Concentrated iodide solutions are obtained by heap leaching of old waste dumps (tailings) and low grade nitrate caUche, such as blasted overburden, left over by former nitrate producers. 

Copper ore minerals maybe classified as primary, secondary, oxidized, and native copper. Primaryrninerals were concentrated in ore bodies by hydrothermal processes secondary minerals formed when copper sulfide deposits exposed at the surface were leached by weathering and groundwater, and the copper reprecipitated near the water table (see Metallurgy, extractive). The important copper minerals are Hsted in Table 1. Of the sulfide ores, bornite, chalcopyrite, and tetrahedrite—teimantite are primary minerals and coveUite, chalcocite, and digenite are more commonly secondary minerals. The oxide minerals, such as chrysocoUa, malachite, and azurite, were formed by oxidation of surface sulfides. Native copper is usually found in the oxidized zone. However, the principal native copper deposits in Michigan are considered primary (5). 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

At the stage of Kuroko mineralization, evolved reacted seawater enriched in Eu, Ca, and Sr formed at low seawater/rock ratio (ca. 1 by mass) and at relatively reduced condition (Eu +/Eu + greater than 1). Selective leaching of Eu, Ca and Sr occurred from the dacitic rocks underlying the Kuroko ores. The hydrothermal solution enriched... 

Considerable changes in the chemical composition of rocks occur during the advanced argillic alteration. For example, Si02 content of highly silicified rocks of the Ugusu silica mine reaches 99% (Iwao, 1962). This silicification is caused by the considerable leaching of elements from the rocks by acid hydrothermal solution except Si and addition of Si from hydrothermal solution. 

D and 8 0 data on fluid inclusions and minerals at main stage of epithermal Au-Ag mineralization clearly indicate that the dominant source of ore fluids is meteoric water. Meteoric water penetrates downwards and is heated by the country rocks and/or intrusive rocks. The heated water interacts with country rocks and/or intrusive rocks and extracts sulfur, Au, Ag and other soft cations (e.g., Hg, Tl) from these rocks. If hydrothermal solution boils, it becomes neutral or slightly alkaline, leading to the selective leaching of soft cations such as Au, Ag, Hg and Tl from country rocks. However, a contribution of sulfur gas and other components from magma cannot be ruled out. 

D and 5 0 data on fluid inclusions and minerals, 8 C of carbonates, salinity of inclusion fluids together with the kind of host rocks indicate that the interaction of meteoric water and evolved seawater with volcanic and sedimentary rocks are important causes for the formation of ore fluids responsible for the base-metal vein-type deposits. High salinity-hydrothermal solution tends to leach hard cations (base metals, Fe, Mn) from the country rocks. Boiling may be also the cause of high salinity of base-metal ore fluids. However, this alone cannot cause very high salinity. Probably the other processes such as ion filtration by clay minerals and dissolution of halite have to be considered, but no detailed studies on these processes have been carried out. 

The studies on the hydrothermal systems at midoceanic ridges during the last three decades clearly revealed that the seawater-basalt interaction at elevated temperatmes (ca. 100-400°C) affects the present-day seawater chemistry (Wolery and Sleep, 1976 Edmond et al., 1979 Humphris and Thompson, 1978). For example, a large quantity of Mg in seawater is taken from seawater interacting with midoceanic ridge basalt, whereas Ca, K, Rb, Li, Ba and Si are leached from basalt and are removed to seawater (Edmond et al., 1979 Von Dammet al., 1985a,b). 

Some trace metals are transported into the ocean as a component of hydrothermal fluids. This process is discussed further in Chapter 19- To briefly summarize, hydrothermal fluids are produced when seawater penetrates into cracks in the crust near tectonic spreading centers. The seawater is heated as it comes into contact with magma. The hot seawater leaches a number of trace metals from the magma. The resulting hydrothermal fluids are acidic and do not contain O2, so most of the metals are present in reduced form. Because of their high temperatures, the hydrothermal fluids have a lower density than cold seawater. Their increased buoyancy causes them to rise until they are emitted into the deep sea. Admixture with cold, oxic, alkaline seawater causes the hydrothermal metals to undergo various redox and precipitation reactions. 

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