Study On Environmental Geochemistry Of Arsenic In Chinese Coals

Arsenic is ranked in Group I environment sensitive element, endangering to the ecosystem environment and human bodies healthily. The problems caused by arsenic contamination have been study widely. Endemic arsenic poisoning in China is widespread and locally very severe. It is very peculiar that the region of arsenism and the number of arsenism people caused by burning high arsenic coals. Based on the progress of study on the arsenic in coals, this dissertation mainly studies the arsenic content, its distribution in Chinese coals and control factors;discuss the mode of occurrence of arsenic in coals;study the arsenic reduction of coals mainly from southwest, which the air was polluted by arsenic;based on the simulative experiment of burning coals, study the mechanism of arsenic release. Based on the study, some conclusions can be drawn.1 , Arsenic content in these coal samples range between 0.24 mg/kg to 71 mg/kg. The average mean of Arsenic is 6.43mg/kg and the geometric mean of Arsenic is 3.96 mg/kg.2, Weighted by the reserves of the five main coal-cumulating areas, arsenic content is 5.28 mg/kg. This value is the arsenic content of whole coals of China, including the coalmine is mined and not mined;Weighted by the coal productions of 26 provinces in 2001, arsenic content is 6.0 mg/kg. This value is the arsenic content of whole coals that had mined;The influence of high arsenic coal from Guizhou Province can be ignored because the reserve is very small.3 , Compared with the coals from around the world, the average arsenic contents arelower. The health problems in China derived from in coal (arsenism) are duelargely to poor local life-style practices in cooking and home heating with coalrather than to high arsenic contents in the coal.4, The arsenic contents decreases with coal forming in the order: Tertiary > EarlyJurassic > Late Triassic > Late Jurassic > Middle Jurassic > Late Permian > Early Carboniferous > Middle Carboniferous > Late Carboniferous > Early Permian;The arsenic contents decreases with coal rank in the order: he>fei> chanyan > shou > pin > wuyan > jiao > qi. But it is meanlsss. The concentrations of arsenic in coals are affected by many factors. Source material, depositional environment, climatic and hydrologic conditions are the controlling factors of trace elements during the early stages of coal formation. However, rank, tectonic setting and geochemical nature of groundwater and country rocks have greater influence during the coalification stages. Most of these factors are regional. So it is difficult to found a relationship between arsenic contents of Chinese coals and coal-forming periods and coal ranks.5> There is not relationship between arsenic content and ash content in all coal samples. With the increase of ash content, arsenic content is not increase. When the ash content locate in 0 to 15%, the relationship between arsenic content and pyritic sulfur is very good;When the ash content range from 0 to 25%, the relationship between arsenic content and sulfate sulfur is found;There is good relationship between arsenic content and organic sulfur in high ash content coals. The arsenic probably presents mainly in organic matters.6> There is good relationship between arsenic content and sulfur, pyritic sulfur, sulfate sulfur, organic sulfur in all coal samples. With the increase of sulfur content, the number of high arsenic coal is increased too. When the sulfur content is lower than 0.5%, arsenic contents has no relativity with them;When the sulfur content locate in 0.5% to 1.5%, the relationship between arsenic content and pyritic sulfur, sulfate sulfur, sulfur is good;When the sulfur content is higher than 1.5%, only the relationship between arsenic content and sulfur is found. In lower sulfur and high sulfur coals, arsenic maybe presents in form of various matters. In other coals? although the mode of arsenic is very complicated, arsenic mainly presents in form of sulfur.7^ Physical coal cleaning techniques are effective in arsenic, ash and sulfur reduction. When arsenic content lower than 5.5 mg/kg, arsenic will mainly or wholly occursin organic matter and occurs in mineral which be enwrapped by organic matter, So it is difficult to remove arsenic and arsenic will enrich in washing coals. When arsenic content higher than 5.5 mg/kg, arsenic will mainly in mineral. The arsenic of coal can be wiped off easily.8> The volatility of arsenic increases along with the temperature. During 800 °C to 1200°C, the volatility of arsenic change greatly.