Oxidation reactions, mineral

There are numerous synthetic and natural compounds called antioxidants which regulate or block oxidative reactions by quenching free radicals or by preventing free-radical formation. Vitamins A, C, and E and the mineral selenium are common antioxidants occurring naturally in foods (104,105). A broad range of flavonoid or phenoHc compounds have been found to be functional antioxidants in numerous test systems (106—108). The antioxidant properties of tea flavonoids have been characterized using models of chemical and biological oxidation reactions. 

Kinetic mles of oxidation of MDASA and TPASA by periodate ions in the weak-acidic medium at the presence of mthenium (VI), iridium (IV), rhodium (III) and their mixtures are investigated by spectrophotometric method. The influence of high temperature treatment with mineral acids of catalysts, concentration of reactants, interfering ions, temperature and ionic strength of solutions on the rate of reactions was investigated. Optimal conditions of indicator reactions, rate constants and energy of activation for arylamine oxidation reactions at the presence of individual catalysts are determined. 

Oxidation of H2S (reaction (1-35)) occurs under the near-surface environment. Oxygen may be supplied from oxygenated groundwater. These oxidation reactions liberate H+ ion, leading to a decrease in pH. Under low pH conditions intermediate argillic alteration minerals (e.g., kaolinite, sericite) are stable. 

In the leaching process, bacteria such as Thiobacillus ferroxidans and those belonging to the Sulfolobus genera, play a major role in the oxidation reactions at moderate and higher temperatures respectively. The oxidation of sulfides by bacteria is typified by the reactions of pyrite, a common accessory mineral in primary copper ore bodies this reaction can be considered to proceed through two stages ... 

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. 

Rates of reductive dissolution of transition metal oxide/hydroxide minerals are controlled by rates of surface chemical reactions under most conditions of environmental and geochemical interest. This paper examines the mechanisms of reductive dissolution through a discussion of relevant elementary reaction processes. Reductive dissolution occurs via (i) surface precursor complex formation between reductant molecules and oxide surface sites, (ii) electron transfer within this surface complex, and (iii) breakdown of the successor complex and release of dissolved metal ions. Surface speciation is an important determinant of rates of individual surface chemical reactions and overall rates of reductive dissolution. 

Coordinative Environment. The coordinative environment of transition metal ions affects the thermodynamic driving force and reaction rate of ligand substitution and electron transfer reactions. FeIIIoH2+(aq) and hematite (a-Fe203) surface structures are shown in Figure 3 for the sake of comparison. Within the lattice of oxide/hydroxide minerals, the inner coordination spheres of metal centers are fully occupied by a regular array of O3- and/or 0H donor groups. At the mineral surface, however, one or more coordinative positions of each metal center are vacant (15). When oxide surfaces are introduced into aqueous solution, H2O and 0H molecules... 

Photocatalysis over oxide semiconductors has been proposed as an effective, mild and environmental friendly technique for the abatement of (refractory) organic contaminants with oxygen as electron acceptor [15]. In this case the reaction is normally exoergonic, as the overall reaction (mineralization) is organics + yC>2 = xCC>2 + ZH2O. 

For the case that the hydrophobic entity is disulphide, the mineral will be depressed when the reaction of the type (2-3) or (2-4) occurs before the reaction (1-3). Thus for the pyrite /diethyl dithiophosphate (DTP) system, pyrite will be depressed if the oxidation reaction... 

The density of the corrosive current of jamesonite in NaOH solution is basically the same as that in Ca(OH)2 solution, but it is minimal in Na2C03 solution, about a fraction of the fourth of the former. There are obvious appearances of passivation and its breaking-down in strong polarization area in NaCOa solution Because COj ion is easier to form insoluble alkaline carbonate than OH ion, the carbonate salts are passive on the mineral surface to inhibit oxidation reaction. 

Abstract The flotation mechanism is discussed in the terms of corrosive electrochemistry in this chapter. In corrosion the disolution of minerals is called self-corrosion. And the reaction between reagents and minerals is treated as inhibition of corrosion. The stronger the ability of inhibiting the corrosion of minerals, the stronger the reagents react with minerals. The two major tools implied in the research of electrochemical corrosion are polarization curves and EIS (electrochemistry impedance spectrum). With these tools, pyrite, galena and sphalerite are discussed under different conditions respectively, including interactions between collector with them and the difference of oxidation of minerals in NaOH solution and in lime. And the results obtained from this research are in accordance with those from other conventional research. With this research some new information can be obtained while it is impossible for other methods. 

In batch kinetic tests, Yan and Schwartz (1999) investigated the oxidative treatment of chlorinated ethylenes in groundwater using potassium permanganate. 1,1-Dichloroethylene reacted more quickly than cis- and /ra/ 5-l, 2-dichloroethylene, trichloroethylene, and tetrachloroethylene. The reaction rate decreased with an increasing number of chlorine substituents. The pseudo-first-order rate constant and half-life for oxidative degradation (mineralization) of 1,1-dichloroethyene were 2.38 x 10 Vsec and 4.9 min, respectively. 

The preparation of 1,3-azoles (benzoxazoles, benzimidazoles and benzothiazoles) from oximes using oxidants on mineral supports such as Ca(0Cl)2/Al203 or Mu02/Si02 or by fusion in dry media has been described. Eor instance, benzoxazoles 232 can be obtained by reaction of o-aminophenols (R, R = H, N02,C1) with substituted beuzaldehyde oximes 231 in the presence of Ca(0Cl)2/Al203 under microwave irradiation (equation 100). ... 

Thermal decomposition yields copper(II) oxide. Reactions with mineral acids yield the corresponding copper(II) salts ... 

Several nickel salts are obtained by reactions of nickel oxide with mineral acids. Thus, the reaction of black nickel oxide with hot dilute sulfuric acid forms nickel sulfate, NiS04 6H2O. Similarly, dilute nitric acid, hydrochloric, and hydrobromic acids when heated react with the black form of nickel oxide to yield corresponding nickel salts as hexahydrates. 

An oxidation reaction is so named because it used to refer to chemical activities involving oxygen, such as combustion. The term combustion is presently used in a broader sense, and it describes a process by which an element increases its oxidation number. An oxidation number is an abstraction—chemists assign this number based on a set of rules, which helps them understand reactions. Oxidation corresponds to a loss of electrons. Reduction, on the other hand, corresponds to a gain in electrons. Miners and metal producers have long used reduction... 

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