Study On Interface Reactions Of Iron And Manganese Oxides And Their Implication In Environmental Mineralogy

Nowadays, the application of mineralogy in environmental sciences is a major aspect of mineralogical studies. Reactions at the mineral-water interface play an important role in the cycling of matter in the environment as well as the geochemical processes of elements. Iron and manganese oxides are ubiquitous in soils. Natural oxides of iron and manganese with surface charges and variable valence elements have favorable surface activities. Being the typical and potential oxidants, they can decompose and oxidize reducing phenolic compounds in sedimentary environment, and the oxidative degradation abates poison to fauna and flora. Focusing on the reactions at the mineral-water interface, this dissertation takes iron and manganese oxides as a main subject of investigation. It gives, at first, a brief review of internal and external contributing factors of contaminated soil and various remediation methods, and then the interface reactions between five species of phenolic compounds and iron and manganese oxides in detail. This includes the determination of gross reducible iron and manganese oxides, their soluble behavior and the kinetics of redox reaction between iron and manganese oxides and phenolic compounds. Finally, the reductive dissolution of natural minerals in soils in tropic and subtropic zones by phenolic compounds in comparison with corresponding synthetic minerals it also given.Conclusions of this work were drawn as follows:(1) The magnitude of reaction rate between iron and manganese oxides in soils and phenolic compounds is as follows: LZ > XW1 > XW2 > HA > ZJ > YS for iron oxides in soils, and HA > XW1 > XW2 > LZ > YS > ZJ for manganese oxides in soils. The pH value of buffer solution affects the degree of degradation of phenolic compounds by iron and manganese oxides.(2) The reductive dissolution of natural and synthetic goethite in the presence of phenolic compounds follows the kinetic equation of the zero-order reaction when pH value is invariant and phenolic compounds are superfluous. The dissolution intensity is negatively correlated to the pH value of buffer solution, and the variation of pH value has more effect on the dissolution of natural goethtie than that of the synthetic.Under the same condition, the reductive dissolution of manganese oxide follows a pseudo-first-order kinetic rate law at its initial stage. Deviations from pseudo-first-order behavior are also observed when the reactions are monitored over a longer period. These deviations may attribute to the changes of apparent rate constant k. With the decreasing of pH in solution or increasing of the reaction temperature, the k value of phenolic compounds goes up with no exception.(3) Natural goethite has the ability to degrade phenolic compounds better than synthetic goethite. With the increasing of reaction temperature, the mass-normalized zero-order dissolution rate coefficients of natural and synthetic goethite go up when pH value is invariant, but go down with the increasing of pH value at the same reaction temperature. In general, the mass-normalized dissolution rate coefficients of natural goethite is larger than that of synthetic goethite. The smaller the pH value, the greater the difference of their coefficients. However, when pH value is invariant, the difference goes up with the increasing of reaction temperature, and it becomes more obviously when the pH value is getting lower.(4) During the kinetic redox reaction between phenolic compounds and iron and manganese oxides, adsorption process by soil, iron and manganese oxides and their impurity is happened. It is revealed that the oxidation rate of phenolic compounds follows the pseudo-first-order reaction at its initial stage if the influence of adsorption and other processes is ignored.(5) Experiments show that reducing of pH value will increase the reductive dissolution of manganese oxides. The variation of dissolution intensity with pH value follows the first-order exponential decay equation magnificently. It is also found that the influence of pH...