An Experimental Study On Kinetic Oxidation-dissolution And Reactive Transference Of Thallium Minerals In Hypergene Condition

The Lanmuchang thallium deposit in Xingren County, Guizhou Province, is the unique independent thallium deposit in the world. For many years, amounts of unpicked up and unutilized thallium minerals have been stacked on the Earth's surface in that region. Thallium entered into local water and soil by weathering and leaching process, and were exposed in body of local people by food chain. During the period of 1960s and 1970s, a population of approximately 1000 people in Lanmuchang had been affected by Tl poisoning. They suffered poisoning and causal hair loss, reduced vision, lost labor force even blindness. The thallium poisoning case is one of the most serious health problems resulting from environmental pollution. Thallium is not necessary element to human body, trace thallium in the body will be harmful. The current China Maximum Contaminant Level (MCL) is lug/L in drinking water. It is very important to carry out the kinetic study of the oxidation and reactive transference of Tl in hypergene condition.From the oxidation-dissolution experiment of Lorandite in acidic mine water, the photochemical reaction of Tl in aqueous solution and Tl adsorption experiment by iron in acidic mine water, some conclusions can be drawn as follows:I . The results from the kinetic study of the oxidation-dissolution of Lorandite showed that the rate of oxidation of Lorandite was affected by the temperature of solution, the concentration of oxidant and kinds of anion in the oxidant. The rate of oxidation of Lorandite was increased or decreased along with the increasing of the temperature and the concentration of oxidant, respectively. This is because that the surface of Lorandite will form the film formed by sulfur and iron when concentration of iron is high, and this film will prevent from dissolution of Lorandite. Tl minerals polluted severely the environment when they were exploited early days, but the pollution will decrease after weathering-leaching. The pollution will increase againafter the oxidative film of Lorandite being destroyed.The oxidation-dissolution of Lorandite in acid mine water is one of the important sources of thallium pollution in Lanmuchang regions, Xingren County, Guizhou Province in according to the total thallium contents of soluble Lorandite in 24 hours.II. A photooxidation experiment of thallium showed that Tl( I) can be oxidized to Tl(III) under photoirradiation of the high-pressure mercury arc lamp and solar light. The photooxidation rate of thallium can be affected by the pH of the solution, intensity and wavelength of the light source. Lowering of the pH and increasing of the light intensity have the effect of increasing of the photooxidation rate. UV radiation (UVB and UVC regions) played an important role in the photooxidation of Tl( I). However, the microbial effect was not obvious in comparison with photooxidation effect in this experiment.III. The results of Tl adsorption by iron showed that the absorption of Tl by ferrous hydrate could be affected by pH of solution and the concentration of iron, especially the valence state of Tl. T1(I) can be absorbed by ferrous hydrate, especially in the Cl" solution, and the absorption rate is about 50%, but less than 20% in the SO42" solution. T1(I) absorbed by iron in alkaline (pH= 10)solution is stronger than that of the neutral solution. Tl(III) and Fe(III) coprecipitation and Tl(III) can be completely absorbed by iron in the neutral or alkaline (pH= 10) solution and different anion solution because of the hydrolysis of Tl(III).This study has provided a good method handing with thallium pollution. We combined the experiment of photooxidation. T1(I) can be oxidized to Tl(III) by light, then fixed Tl(III) by utilizing the characters of Tl absorption or coprecipitation. This can reduce thallium mobility and make effects on the aquatic environment.