中国部分城市铂族元素环境地球化学特征研究

自上世纪90年代起,汽车工业中大量引入铂族元素催化剂,将有害气体转变为二氧化碳和氮气,以降低这些温室气体的排放。但铂族元素催化剂释放的Pt,Pd和Rh等元素在城市道路尘土和路边土壤中聚积,其含量大大的超过正常背景值。本次研究在深圳,广州,北京和贵阳等城市的主要交通路段采集了尘土、土壤及新鲜土壤样品,采用改进的卡洛斯管法和蒸馏法对样品中的全部铂族元素进行了分析。结果表明,所有样品的铂族元素含量均高于背景值,尘土样品中铂族元素含量明显高于土壤样品,其中Pt,Pd,Rh含量明显高于其它铂族元素,并呈正相关,表明汽车尾气催化剂的主要组成为Pt,Pd,和Rh。所有样品Ru,Ir和Os的含量都明显高于背景值,具有高含量的Os、低的187 Os/188 Os比值特征,表明Ru,Ir和Os也来源于汽车尾气催化剂,并且可能以杂质的形式存在于汽车尾气催化剂中。

Environmental Geochemical Characteristics of Platinum-group Elements in Some Major Cities of China

The platinum-group elements(PGEs)(mostly,Pt,Pd and Rh) have been used as automobile catalytic converters in automobile industry to transform greenhouse gases,such as carbon monoxide,nitrogen oxides(NOx) and hydrocarbons to carbon dioxide,nitrogen,and water since 1990.Although automobile catalytic converters can reduce the exhaust of greenhouse gases,the emission of PGEs has led to the concentration of PGE in road dusts and roadside soils in urban areas that are well above natural background levels.Reported in this paper is the evaluation of contamination of all the PGEs and Au recorded in road dusts and roadside soils from the four major cities: Beijing,Shenzhen,Guangzhou and Guiyang in China.Samples were digested with a carius tube and analyzed by isotope dilution ICP-MS,Os was separated by distillation and the other PGEs by Te-coprecipitation.PGE concentrations of all the samples have been elevated above the background values of uncontaminated soil,and higher Pt,Pd and Rh contents than the other PGEs.There are clearly positive correlations between Pt and Pd,Pt and Rh and Pd and Rh for all the samples,indicating that the compositions of automobile catalyst are Pt,Pd and Rh.The concentrations of Ir,Ru and Os in all the samples are higher than the background values of uncontaminated soil.Dust samples with higher Os contents have lower 187Os/188Os ratios,suggesting that Ir,Ru and Os come also from automobile catalytic converters,and may be present as impurities of the automobile catalysts.