| Chromium (heavy metal) is an element widely used in industries, such as electroplate, pigment, paint, metal alloy, dying and so on. On the other hand, the unproper disposal of the wastes and rubbishes containing chromium is danger to plants, animals and human being. So, how to control and reduce the pollution of the environment from chromium has a strong appeal to the researchers of the environment defence. Chromium exists mainly in two forms of Cr(VI) and Cr(III). Cr(VI) is strong oxidization, high toxicity and is easily transferred in the environments; but Cr(III) is hard to transfer and low toxicity. So, people usually treat Cr(VI) to Cr(III) by reductants to reduce its toxicity to environment. The kinetics of reduction of Cr(VI) by pyrite(FeS2) and zero-valent ion and their impact factors were studied in this paper.In chapter one: The effects of temperature, pH and density of pyrite in suspension on Cr(VI) reduction by pyrite were studied. The results showed that rate of removal of Cr(VI) by pyrite increased with temperature, acidic degree and density of pyrite. Both Fe(II) and S2(-II), consisted of pyrite, reduced Cr(VI) to Cr(III) effectively. The dissolution of pyrite in acidic solution was relatively fast and easily reached to dissolution equilibrium. But, residue of pyrite after the reaction dissolved rather slowly, partially resulting from the covering of the product of CrxFe1-x(OH)3.In chapter two: The influence of pH, EDTA and NaF on the reduction of Cr(VI) by zero-valent ion was conducted under constant temperature and anaerobic condition. The results showed that pH played an important role in the reduction of Cr(VI) by zero-valent ion powder. The reaction rate between zero-valent ion powder and Cr(VI) was fast with pH less than 4.0 and very slow with pH>5.0 except for the initial phase of reaction. EDTA with a concentration of 0.40-4.0 mmol·L-1 accelerated the Cr(VI) reduction by zero-valent ion remarkablely. In the presence of EDTA, the reduction of...
|
PDF Full Text Request