Upper oxidizing zone

The geochemical environments within the upper 1.5 meters of reservoir sediments were first described by Moore et al. (1988). They found an upper oxidized zone in only the upper few centimeters of subaerially exposed sediment, beneath which saturated sediment was dominated by anoxic conditions. Udaloy (1988) found that the anoxic zone extended to the base of... 

There are over 65 known vanadium-bearing minerals, some of the more important are Hsted in Table 1. Patronite, bravoite, sulvanite, davidite, and roscoehte are classified as primary minerals, whereas all of the others are secondary products which form in the oxidizing zone of the upper Hthosphere. 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

Preliminary work (10) on the transition from oxidized surface sediment to reduced subsurface sediment in Milltown Reservoir showed that the redox transition occurs in the upper few tens of centimeters. Strong chemical gradients occur across this boundary. Ferrous iron in sediment pore water (groundwater and vadose water) is commonly below detection in the oxidizing surface zone and increases with depth. Arsenic is also low in pore water of the oxidized zone, but increases across the redox boundary, with As(III) as the dominant oxidation state in the reduced zone. Copper and zinc show the opposite trend, with relatively high concentrations in pore water of the oxidized surface sediment decreasing across the redox boundary. 

FeS2 distribution in sediments is primarily controlled by (1) sedimentation of detrital FeS2, (2) FeS2 oxidation in the upper root zone, and (3) FeS2 formation at the interface between suboxic and anoxic zones. 

Discussion. Nitrate is seen to decrease at a water depth of 8 m (15 m below the surface), whereas iron is low at this depth and rises beneath. This indicates the existence of an oxidizing zone in the upper 8 m of water and a reducing zone below. The nitrate was reduced by ferrous iron to N2, which was expelled into the atmosphere. The tritium data were most informative ... 

Upper reducing zone (e) Hottest portion of flame (b) Lower oxidizing zone (c) Lower reducing zone (f)... 

The alteration of all but the most resistant primary minerals occurs in the mid- to upper saprolite zones in addition, less stable secondary minerals such as smectite are also destroyed. Serpentine, magnetite, ilmenite and chlorite are progressively weathered through the zone. Ferromagnesian minerals are the principal hosts for transition metals such as Ni, Co, Cu and Zn in mafic and ultramafic rocks they become leached from the upper horizons and reprecipitate with secondary Fe-Mn oxides in the mid- to lower-saprolite. 

In 2002 twelve groundwater samples were taken from 6 different wells (see Fig. 1). The wells were chosen to represent different areas of the groundwater contamination Sample A was taken in a region upstream of the potential emission source, sample B was located directly in the emission area, whereas samples C to F were situated downstream of the local contamination. With respect to changing chemical conditions within different vertical layers (e.g. varying oxidation-zones) half of the samples were taken from the upper (samples a-f) and the lower (samples A-F) part of the aquifer, respectively. The position of the investigated wells relative to the emission source as well as the depth of the sample points are shown in Tab. 2. Each well was pumped at all horizons simultaneously for 30 minutes at 2 m3/h to avoid vertical mixing. 

Upper intermediate zone Spodumene, quartz, amblygonite MicrocUne—perthite, pollucite, Uthiophilite (albite, Li-muscovite), (petaUte, eucryptite, Ta-oxide minerals) Giant crystal size of major and most of the subordinate minerals Li, P, F (K, Na, Cs, Ta)... 

The oxygen in the blast penetrates but a short distance above the tuyere level. It is all consumed in burning the carbon of the coke to CO. Most of the carbon in the coke descends through the shaft of the furnace until it reaches the tuyere zone, where it is met by the blast and burned to carbon monoxide. The high temperature precludes the formation of carbon dioxide. Some of the carbon, however, through actual contact with iron oxide, is oxidized (either to CO or C02) in the upper part of the furnace. This oxidation, of course, liberates heat above, instead of in, the smelting zone where it is most needed and likewise tends to decrease the proportion of carbon fully oxidized to C02 in the furnace and thereby the quantity of heat developed in the furnace. 

This type contains a variety of ores, including(a) gold-pyrite ores, (b) gold-copper ores, (c) gold-polymetallic ores and (d) gold oxide ore, usually upper zone of sulphide zones. The pyrite content of the ore varies from 3% to 90%. Other common waste minerals are quartz, aluminosilicates, dolomite etc. 

In general, the calceous-dolomitic rocks from the Cambrian age are affected by their upper beds, by sulphide mineralization of lead, zinc and iron contemporaneous with sedimentation. The oxide lead and zinc minerals are disseminated through dolomitic limestone. As a consequence of the action of the descending process, these formations may assume different types of mineralization. According to the intensity of the oxidation process, which is associated with the different characteristics of the country rock, this country rock may be (a) principally calceous, (b) calceous with dolomitized zones and (c) primarily dolomitized. 

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