The Occurrence Characteristics And Environmental Effects Of Trace Elements In Fly Ash

Fly ash is the by-product of coal combustion and the main solid waste discharged from coal-fired power plants.In the process of reclamation,backfilling and storage of fly ash,trace elements enriched in fly ash are easily released into the environment under external forces such as weathering,leaching and so on,which harms the ecological environment.pH is an important factor affecting the leaching behavior of trace elements.Therefore,it is of great significance to study the transport and change characteristics of environmental substances in fly ash under different pH leaching conditions by indoor sandbox simulation test.Taking a fly ash sample of Hefei power plant as the research object,the morphology,mineral composition and element content distribution of fly ash were analyzed by chemical experiment and high precision analysis test.The migration characteristics of environmental substances in fly ash under different pH leaching conditions were discussed.The main research results are as follows:(1)Most of the original fly ash particles are irregular or flaky,at the same time,there are some unburned carbon particles and rough spherical particles.The fly ash particles after leaching are mainly irregular and other morphology was not observed,and there was no significant difference in the micro-morphology of fly ash after leaching with different pH conditions.(2)The basic mineral composition of the original fly ash mainly consists of quartz,calcite,kyanite,dolomite,oblique silica,etc.The basic mineral composition of fly ash after leaching has not changed obviously,and the above five minerals are still the main minerals.Then there was no significant difference in the XRD profiles of fly ash after leaching with different pH conditions.(3)Chromium,zinc,nickel,lead,cobalt and copper are enriched in different degrees in the fly ash,and the enrichment times are above 10 times.The content of six trace elements in fly ash decreased after leaching.The variation trend of element content was similar with the increase of pH value.The release amount was higher in strong acid and strong alkaline condition,but lower in near neutral condition.(4)It is found that the concentrations of Zn,Ni,Pb,Cu and Co elements in groundwater first decrease and then increase with the increase of pH,while the concentration of Cr in groundwater increases first and then decreases with the increase of pH,and reaches its peak when pH=10.In longitudinal distribution,there isno clear regularity of Cr,Cu in groundwater,the concentration of Zn,Ni,Co is higher at pH=2 at 10 cm and at pH=13 at 30 cm,Pb concentration is higher at 10 cm under acidic condition,but no clear rule is found in neutral and alkaline conditions.(5)The contents of Cr in soil decreased at first and then increased with the increase of pH value,and the changes of Zn,Ni,Pb,Cu and Co contents were similar with the increase of pH value.When the pH value was in the range of 2~6.8,the contents of these five elements all decreased.With the continuous increase of pH value,the content of elements increased first to pH=10 and then decreased,and the decrease of Cu content was relatively small.The contents of six trace elements in different depth soil have no significant regularity.The effect of fly ash on soil eco-environment is small under short-term leaching,which can be ignored in general.