Research On Species Of Heavy Metals In Typical By-products From Coal-fired Power Plants

It is obvious that heavy metals are wide spread in the environment,and most of them are toxic.Coal-fired power plants are playing a great roal in heavy metals emission.The amont of by-products from coal-fired power plant is increasing year by year,and most of them are beneficially utilized.Some heavy metals can be released into the environment during the utilization and cause secondary pollution.Thus,it is necessary to study species of As and Hg in by-products from coal-fired power plants.A HNO₃-HF system was utilizated to digested the samples and the contents of arsenic in coal,ash,gypsum and slag which were determined in the samples collected from 11 coal-fired power plants.The contents of arsenic varied among different samples.The concentration（m/m）of arsenic was 2.5-8.0 μg/g in coal,9.39-93.91 μg/g in ash,2.3-19.7 μg/g in slag,and 1.0-3.0 μg/g in gypsum.Correlation analysis showed that arsenic in gypsun mostly came from ash which was captured in desulfuration system.In order to quantify the species of arsenic in the samples,an online coulpling system of high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry（HPLC-HG-AFS）was developed.The method was sensitive,fast and stable for arsenic species analysis.The species and content of arsenic in the different gypsum samples were detected by this system.The results showed that most of water-soluble As in gypsum is in As（III）form.Another online system was also developed for mecury species analysis in gypsum.The pyrolysis tempretures of different compounds of mecury were meseared by the system.We found that the different compounds have their own pyrolysis tempretures.The temperatures were in the following order: HgCl2 < HgS（black）<HgO < HgS（red）< HgSO4.Tempreture programming was utilized to separate different mecury compounds,and the signal was detected by AFS.The gypsum samples from different power plants were analyzed using this system.HgO and HgS had greater signal than others,whitch meant that mecury compounds in gypsum mostly consisted of HgO and HgS.