Study On The Regularity Of Leaching, Releasing And Transfer Of Carcinogen Chromium Of Coal And Its Products In Rich Coal Area Of Yunnan Province

Being one of common malicious trace elements in coal,chromium mainly takes two forms:chromium(â…¥)and chromium(â…¢),each of them displaying striking differences in mobility and toxicity for that the former is highly toxic,soluble and cancerogenic whereas the latter is much less toxic and has a strong affinity for soil particle surfaces.Xuanwei is an important coal producing area in Yunnan and it is also a high-incidence area of cancer in China.The malicious influences chromium has on the local environment can not be neglected for that the poisonous elements of chromium can leach and release from coal and its products(coal gangues and fly ash),resulting from rainwater's leaching and scouring of many fields of coal heaps,coal gangues as well as fly ash in Xuanwei.The chromium in leaching solution could transfer into and then pollute the soil and the groundwater, threatening badly the local people's health.The current research takes Laibin town in Xuanwei as the research area and by analyzing the samples of the coal,coal gangue and fly ash collected from the research area and then by making batch leaching and column leaching experiments,the author gained the data which showed that the pH value of the leaching solution,the shaking time,the existing form as well as the content of chromium were those factors which influenced chromium's leaching and releasing from coal and its products.By contrasting the leaching intensities of chromium among various samples,the author also found that Cr(â…¥)leached easier in fly ash than in coal and coal gangue.The leaching intensities of total Cr,however,were very low and of little difference,showing that Cr(â…¥)was the main leaching form from coal and its products.Based on the parameters gained from column leaching experiment,the leaching and releasing model of chromium in coal and its products was deduced and by predicting the annual average releasing concentration of Cr(â…¥)in coal and its products,the author found that the concentration of Cr(â…¥)in fly ash was 0.075mgL^-1which exceeded the current Chinese drinking water quality standard(GB5749-2006).The soil and groundwater, therefore,was threatened.In addition,the experiment on the adsorption and transfer of Cr(â…¥)in the soil of aeration zone confirmed that the adsorption capacity of Cr(â…¥)was very low in alkalescent soil of aeration zone.It also showed that the adsorption mode was Henry adsorption model and the adsorption coefficient was 1.1577.The transfer of Cr(â…¥)was somewhat delayed in alkalescent soil comparing to that in conservative matter.By using HYDRUS-1D software and convection-dispersion equation,the author respectively conducted several hypothetical experiments to find out the transferring and changing conditions of Cr(â…¥).The results showed that,when the thickness of the aeration zone was 4m,5m and 6m,the Cr(â…¥)concentration of leaching solution would all exceed the limit of 0.05mgL^-1with the fly ash's deposition time of 0.89a,1.4a and 2.01a.This amount of Cr(â…¥)concentration would pollute the groundwater and harm local people's health.The author,therefore,proposed the suggestion that anti-seepage measure should be adopted in both the temporary and permanent fly ash fields.In so doing,the pollution of Cr(â…¥)in the leaching solution towards the groundwater and the soil could be prevented.