Catalysis Of Al(â…¢) And Fe(â…¢) On Cr(â…¥) Reduction By Organic Acid

Chromium (Cr) is widely used in industries, such as steel production, leather tanning, corrosion prevention, dye, tannery industry and galvanic. As a result of unproper disposal of the wastes containing chromium, chromium danger to human, animals and plants has become one of the most serious environmental contaminants. Chromium mainly exist in two forms in natural environments: Cr⁶⁺ and Cr³⁺. These two forms exhibit completely different mobility and toxicity. Cr⁶⁺ is high toxicit and solubile. However, Cr³⁺ is much less toxic and has a strong affinity for soil particle surfaces, displaying immobility. So, Cr⁶⁺ is often reduced to Cr³⁺ by chemical reduce agents to control chromium contamination. In the paper, we mainly discuss that the catalysis of Al³⁺ and Fe³⁺ with light. on the reduction of Cr⁶⁺ by organic acid.In chapter I, We study that the catalysis of Al³⁺ on the reduction of Cr⁶⁺ by citrate acid, tartaric acid, oxalate acid, butyric acid, laetrile acid and malic acid at different temperatures and pH. The results show that the reaction will be more quick in the presence of Al³⁺. Visibly, Al³⁺ can catalyze the reduction of Cr⁶⁺ by tartaric acid. This catalysis is more obvious when the temperature is higher, the pH is lower and the concentration of Al³⁺ is thicker. A zero-order kinetics is used to describe the reduction of Cr⁶⁺ by tartaric acid in the presences of Al³⁺. In addition, we study the effect of Al³⁺ on the reduction of Cr⁶⁺ by other organic acids, and discover that only the organic acid with oxhydryl inα-position can speed up the reduction of Cr⁶⁺. This is because these organic acid can easily form chelate with Al³⁺, which accelerate the reduction of Cr⁶⁺.In chapterâ…¡, The catalysis of Fe³⁺ with light or without light on the reduction of Cr⁶⁺ by organic acids. The results show that Fe³⁺ without light can not accelerate Cr⁶⁺ reduction by organic acid. However, Fe³⁺ with light can accelerate Cr⁶⁺ reduction by organic acid, which shows Fe³⁺ can photocatalyze organic acid to reduce Cr⁶⁺. This behaviour is very practical. The reason is that Fe³⁺ can combine with organic acid to form a new complex material quickly, which can produce Fe²⁺ and organic flee radical, The Fe²⁺ and organic free radical can reduce Cr⁶⁺ to Cr³⁺, and Fe²⁺ will be oxidized to Fe³⁺. The Fe³⁺ will combine with organic acid, and Fe²⁺ and organic free radicals are preduced again. So, in the reaction system circle catalysis system forms, which accelerate the reduction of Cr⁶⁺ by organic acid greatly.In chapterâ…¢, The effects of three minerals kaolinte, montmorillonite, illite on the reduction of Cr⁶⁺by citrate acids with light or without light are compared at the same temperature and pH. The results show that when the three minerals exist, the reduction of Cr⁶⁺ by citrate acid with light will be faster than that without light. Some Fe³⁺ attached on the minerals photocatalyzes the reduction of Cr⁶⁺ by citrate acid in light. However, the effects of minerals on Cr⁶⁺ reduction could be reduced remarkably when 0.1M NaF was intraduced to the reaction sqctere. This is because F^- and Fe³⁺ form FeF₆^{3_</sup>, which eliminates Fe3+ catalysis from minerals on the reduction of Cr6+ by organic acids with light.}