锌冶炼烟尘中铅汞分布及形态研究

锌精矿脱硫焙烧烟气降温过程中,烟尘的性质及其中铅汞存在形态的变化规律是冶炼烟气重金属(Pb和Hg)污染控制的重要依据。通过电感耦合等离子体-原子发射光谱(ICP-AES)、激光粒度分析及筛分分析了不同降温收尘环节烟尘元素成分及粒度变化。烟尘主要含Zn、Fe、Ca、Cd、S、Pb元素,其累积质量分数达69.90%~77.62%,而Hg含量较低。烟尘粒径随烟气温度降低呈先增大后减小的变化规律,中位径由沸腾焙烧炉排出的28μm升至经余热锅炉降温后的36μm,再逐级降至经电收尘器后的5.6μm。据此,重点分析了Pb和Hg在烟气中的分布,并借助X射线光电子能谱(XPS)分析了其存在形态。结果表明,随烟气温度降低,烟气中Pb和Hg含量呈上升趋势,Pb由2.8%增至9.2%,Hg由4.8μg/g增至109.1μg/g。不同工艺环节的烟尘中Pb均以PbSO_4和含Pb—O键的复杂Pb配合物的形式存在。Hg变化较为明显,仅沸腾焙烧炉烟尘样品中能够检测到HgS与HgSO_4,其余工艺环节烟尘样品中无含Hg化合物的特征峰。

Distribution and species of lead and mercury in flue dust from zinc smelting

The paper is inclined to make an investigation of the properties and configuration variations of Pb,and Hg in flue dust boiling-roasting process of zinc smelting.For the research purpose,we have collected samples from the outlet of boiling-bed roaster (900-950 ℃),the waste heat boiler (at the temperature of 300-450 ℃),the inlet and outlet of a cyclone dust collector (200-300 ℃) and the ash storage warehouse of an electric dust collector (below 2.30 ℃) in a large traditional zinc smelter in Hunan,which are expected to provide significant information and data in controlling the contents of heavy metals (Pb,Hg) in the metallurgical off-gas.When we analyzed the composition of the flue dust samples by using an inductively coupled plasma-atomic emission spectrometry (ICP-AES),we have found the flue dust mainly consisting of Zn,Fe,Ca,Cd,S and Pb that accounts for 69.90％-77.62％ with a low concentration of Hg.In addition,we have also analyzed the particle size distribution of the flue dust samples both by the laser particle size analysis method and the traditional screening particle size analysis method.The results show that the particle size of the flue dust samples tend to increase and then decrease,and the median diameter increases from 28 μm of particles discharged from the boiling-bed roaster to 36 μm of particles discharged from the waste heat boiler,and then gradually reduces to 5.6 μm with the falling of temperature at different stages of dust removal.Furthermore,we have also analyzed the content distribution of Pb and Hg in the flue dust and tested their species via X-ray photoelectron spectroscopy (XPS) analysis.The results of the aforementioned testing and experiment with the entire XPS scanning spectra show that with the decrease of the temperature,the contents of Pb and Hg both in the flue dust tend to show an ascending trend,varying from 2.8％ to 9.2％ and from 4.8 μg,/g to 109.1 μg/g,respectively.Furthermore,XPS fine spectra show that the species of Pb have no obvious variation in different flue dust samples,which exist mainly in the form of PbSO4 and complexes containing Pb—O bond.However,Hg species tend to vary noticeably,though it is easy to find HgS and HgSO4 only in the flue dust of boiling furnace,there can not be found the characteristic peaks of compounds containing Hg in other processes.