Hydrothermal processing process water, composition

Minerals derived from evaporation of saline solutions have not been extensively examined. Evaporitic salts from the western U.S. Great Basin concentrated Li (5 Li = +31.8 to +32.6 Tomascak et al. 2003). Evaporation of thermal waters from Yellowstone yielded travertine with extremely low 5 Li (-4.8 Sturchio and Chan 2003), offset from its coexisting fluid by -ll.l%o. Such evaporites, where preserved in the sedimentary record, could afford an opportunity to examine variations in spring water compositions and hence information on hydrothermal processes over time. 

Clnysotile belongs to the serpentine group of minerals, v arieties of which are found in most of the important mountain ranges and precambrian shields (8). Only a small part of these serpentine occurrences are in the asbestiform clnysotile variety. Chrysotile fibers are found as veins in serpentines or related minerals in serpentinized ultramafic rocks and in serpentinized dolomitic marbles (9). It has been suggested that the ultrabasic rocks (forsterite, Mg-rich pyroxenes, and ampliiboles) are first attacked in an hydrothermal process and transformed in serpentines in a later hydrothermal event, the serpentines are partially redissolved and crystallized as chrysotile fibers (9). (Heady, the genesis of each chrysotile deposit must have involved specific features related to the composition of the precursor minerals, the stress and defomiations in the host matrix, the water content, the temperature cycles, etc. Nonetheless, it is generally observed that the chemical composition of the fibrous phase is closely related to that of the surrounding rock matrix (9). 

In this chapter, we aim to provide an overview of the status of hydrothermal processing technologies and recent research. The chapter includes a description of associated process chemistry including a description of how the properties of water change when heated under pressure and the reaction steps in each of the hydrothermal routes. The impact and influence of different feedstocks on process operation and product distribution and composition is reviewed. Recent advances in reactor design, product upgrading, commercialization and techno-economic and Ufecycle analysis are presented before conclusions are drawn on the status of the technology. 

Oxygen isotopes. 5 0 in ocean-crust studies is typically dehned as the per mil deviation in 180/1 0 ratio of a rock relative to a standard mean ocean water (S Osmow) and it is widely used to understand ocean-crust alteration processes. Fresh MORB has an S Osmow value of - -5.7%o, and water-rock interaction with seawater (S OsMow = at low temperatures increases the value, while high-temperature alteration decreases it. Muehlenbachs and Clayton (1972) drew attention to this relationship and suggested that hydrothermal alteration of the crust may buffer the oxygen isotopic composition of seawater. Oxygen is the major component in the oceanic crust, and therefore, changes in 5 0 are a rather profound indicator of hydrothermal alteration. 

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