The Method For Analyzing Mercury Form In Typical Solid Waste Of Coal-fired Power Plants

In recent years,the pollution of atmospheric pollution of mercury?Hg?had become increasingly serious and caused a global environmental problem.China is the world's largest coal producer and consumer.Therefore,fly ashes,desulfurized gypsums,slags and other coal-combustion by-products?CCBs?will also emit coal-fired solid wastes largely.In the fields of building materials,metallurgy,environmental protection,agriculture etc,the comprehensive utilization rate is high,but the coal-fired by-products have the risk of leaching and re-release during heat treatment or rainfall,especially in the building materials industry,It often need to calcine the materials,which means that the mercury enriched in the fly ash inevitably undergoes a change of the chemical forms during the heat treatment.Therefore,an innovative analytical method is needed to understand more clearly the merury form in coal-combustion by-products.The present study mainly established an equipment suitable for identifying the mercury compounds species in by-products of coal-fired power plants.This study established a new method for the analysis of mercury forms in coal-fired,namely the temperature-programmed pyrolysis-atomic fluorescence spectroscopy combined system to analyze the form of mercury of the coal-fired byproducts.The equipment mainly includes gas path unit,a pyrolysis unit,an atomic fluorescence analysis detection unit,and a data acquisition processing unit.The innovation of this study is to systematically study four solid matrices?fly ash,quartz sand and desulfurized gypsum,anhydrous calcium sulfate?,respectively summarizing the temperature of mercury compounds in the four solid matrices,summarizing the suitable matrix for the analysis of coal combustion.The suitable matrix of mercury for the coal-fired products is mercury-free of fly ash and desulfurized gypsum.The study continued to optimize the new device,and the results showed that the gas flow rate was 600 mL/min,and the second pyrolysis unit temperature was 800°C.The device analyzes the mercury chemical forms in the by-products?desulfurization gypsums,fly ashes,slags?of the coal-fired power plants.The experimental results show that the pyrolysis temperature of mercury compounds with fly ash as solid matrix is Hg₂Cl₂<HgCl₂<Hg₂SO₄<HgO<HgS?red?<HgSO₄,and the pyrolysis temperature of mercury compounds with desulfurization gypsum as solid matrix is sequentially ordered as Hg₂SO₄<Hg₂Cl₂<HgO<HgS?red?<HgCl₂<HgSO₄.Finally,three chemical forms?active mercury,semi-active mercury,inactive mercury?in coal-fired solid waste were analyzed by continuous chemical leaching method?EPA3200?.The species of mercury in fly ash from coal-fired power plants was semi-active mercury range 10.77.%⁸4.43%,the range of inactive mercury is 12.29%⁶0.36%,and the range of active mercury is 3.28%³4.38%.The proportion of mercury-formed active mercury,semi-active mercury and inactive mercury in desulfurization gypsum of coal-fired power plants ranges from 3.39%to 39.14%,6.37to 89.19%,and 32.44%to 89.35%,respectively,to verify the programmed temperature pyrolysis-atomic fluorescence.The results of the two methods together validated the mercury form in solid waste from coal-fired power plants.