| The secondary zinc oxide dust comes from lead, zinc, copper fire smelter. It has the following characteristics: Firstly, it belongs to the hazardous waste. Secondly, it has wide range of sources and large output. Thirdly, the secondary zinc oxide dust enriches a variety of valuable elements in raw materials such as zinc, lead, cadmium, tin, arsenic and so on that it is worth recovery. However, as the elements of lead, cadmium and arsenic from the secondary whose composition is complicated can destroy environment, it increases the difficulty in enriching Cd. A lot of information shows that mineral resources in our country are decreasing day by day. So it is widly concerned to utilize the valuable waste and convert it into resources. The secondary zinc oxide dust is listed as the hazardous waste by "National Hazardous Wastes List". If it is dumped randomly, it will cause tremendous harm to the environment, so it is necessary to seek appropriate approaches about the secondary zinc oxide dust.Through analysing and comparing the research development of recycling valuable metal element from various zinc slag in conjunction with the characteristic of Cd in the secondary zinc oxide dust, this paper got a method that could leach Cd from the secondary zinc oxide dust efficiently with low cost and less environmental pollution. It can reduce the waste residue from industry released to environment. The main contentes the paper studied were as followings:(1)The paper took the secondary zinc oxide dust as research object and simulated three different environmental terms with three different extraction solvents to analyze extaction toxicity in them. The experiment results of extaction toxicity showed that the dust was typically hazardous waste and had strong extaction toxicity. The strongest extaction toxicity was by using the acetic acid method, the next was by using the nitrate-sulfate mixed acid method, the smallest was by using the ionized water method.(2)It studied the leaching kinetics property of the secondary zinc oxide dust in the system of sulfuric acid. It also studied the leaching condition of Cd in that systerm by the single factor and orthogonal experiment. The leaching process of the dust was liquid to solid chemical reaction in the systerm of sulfuric acid. The leaching Cd was controlled by the chemical reaction. An empirical equation for the leaching kinetics was established, which expressed by equaion 1-(1-η)1/3=Kτ, the apparent activation energy of the leaching process was 51.93 KJ/mol.(3)Phase composition and element occurrence in zinc oxide dust were analyzed by XRD instrument. According to leaching kinetics and the single factor experimental results, the optimal leaching condition was studied by orthogonal experiment considered all the affecting factors: the end pH, ratio of liquid and solid, temperature, leaching time and oxidant. With the optimal leaching condition, the leaching rate of Cd could reach up to 99%. the primary and secondary order that was influenced by every factors on leaching rate was: L/S >time >end pH> temperature.
|
PDF Full Text Request