Mineralization partial oxidation products

When an oxidizable organic species R is present in the solution, the physisorbed active oxygen causes predominantly its complete mineralization (reaction (8)), and the chemisorbed active oxygen participates in the formation of partially oxidized products RO (reaction (9)) ... 

The early literature on monoterpene biotransformation was highly influenced by the approach used in steroid biotransformations and mainly focused on terpenoids accumulated by fungal strains which do not mineralize the substrate but partly oxidize it by fortuitous cometabolism. These studies often resulted in the accumulation of a mixture of different products in low yields and at low concentrations [1]. Several bacteria which completely mineralize monoterpenes have been described more recently. It has become obvious from the later studies that multiple pathways are involved in the degradation of monoterpenes in many of these microorganisms, and consequently it has been difficult to obtain mutants allowing the accumulation of partially oxidized products. 

Theoretical calculations [43] based on first principles molecular dynamics discussed in Sect. 3.2.6 have suggested that Mg Al LDHs are most stable for n = 3 (i.e. x = 0.25) and indeed many minerals, including hydrotalcite itself, have this stoichiometry [4]. It has been reported that the synthesis of LDHs (with benzoate or terephthalate anions in the interlayers) from solutions containing Mg/Al = 2, leads to LDHs having the same composition when the synthesis is carried out at moderate temperatures but LDHs with Mg/Al = 3 (plus AlOOH) when the reaction is carried out under hydrothermal conditions [44]. It was proposed that the latter ratio represents the thermodynamically most favorable product. A similar observation has been reported [45] for solutions with Ni VPe = 2, where hydrothermal preparation led to segregation of an LDH with Ni VPe = 3 and Ni Fe 204. An attempt to synthesize a Co sAl LDH resulted in partial oxidation of the Co and formation of a Co o.yCo o.s LDH with complete migration of Al " from the layers to generate interlayer aluminum oxy-species [46]. 

In another study (Watwood, White Dahm, 1991), benzene mineralization occurred in soils incubated under an inert gas for 4 weeks. No attempt was made to remove residual oxygen from these soils and the possibility exists that benzene mineralization may have been linked to the consumption of oxygen. Alternately, it may have been that benzene was partially oxidized by microorganisms and the resulting product was amenable to anaerobic decay. An earlier study (Van Beelen Van Keulen, 1990) showed an extremely rapid rate of benzene mineralization 2% mineralized in 1 h and 5% in 7 days. No samples were taken between 1 and 7 days and further benzene mineralization was not observed. 

Our discussion of mineral surfaces will be restricted to simple oxide and hydroxide minerals that are widely used in adsorption studies (Table 9-1). Under strong weathering conditions, these minerals may comprise a substantial fraction of the available surface area in soils and aquifers. More complex minerals, including parent material and partially weathered products (especially aluminosilicates), are of equal or greater importance in most other subsurface environments. Excellent reviews of the equilibrium and reaction chemistry of aluminosilicate surfaces are available (Voudrias and Reinhard, 1986 Mortland, 1970). 

In an oversimplified way, it may be stated that acids of the volcanoes have reacted with the bases of the rocks the compositions of the ocean (which is at the fkst end pokit (pH = 8) of the titration of a strong acid with a carbonate) and the atmosphere (which with its 2 = 10 atm atm is nearly ki equdibrium with the ocean) reflect the proton balance of reaction 1. Oxidation and reduction are accompanied by proton release and proton consumption, respectively. In order to maintain charge balance, the production of electrons, e, must eventually be balanced by the production of. The redox potential of the steady-state system is given by the partial pressure of oxygen (0.2 atm). Furthermore, the dissolution of rocks and the precipitation of minerals are accompanied by consumption and release, respectively. 

The production of copper from sulphide minerals is accomplished with a preliminary partial roast of die sulphides before reaction widr air in the liquid state, known as mattes, to form copper metal (conversion). The principal sources of copper are minerals such as chalcopyrite, CuFeSa and bornite CuaFeSa, and hence the conversion process must accomplish the preferential oxidation of non, in the form of FeO, before the copper metal appears. As mentioned before, tire FeO-SiOa liquid system is practically Raoultian, and so it is relatively easy to calculate the amount of iron oxidation which can be canned out to form this liquid slag as a function of the FeO/SiOa ratio before copper oxidation occurs. The liquid slag has a maximum mole fraction of FeO at the matte blowing temperatures of about 0.3, at solid silica saturation. 

Dissolution of CaCOs is a congruent reaction the entire mineral is weathered and results completely in soluble products. The above reaction is driven to the right by an increase of CO2 partial pressure and by the removal of the Ca and/or bicarbonate. Any impurities present in the calcareous rock, such as silicates, oxides, organic compounds, and others, are left as residue. As the calcium and bicarbonate leach... 

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