Most of energy consumed in China, now and in the near future, is coal. China is the largest coal producer and consumer in the world. In China coal accounts for 75% of the total consumption of primary energy , It is estimated that coal will take about 67% in the primary energy in 2020, dropping from the present 76%. However, the total consumed coal will be increased to 2.3 billion tons from 1.2 billion tons per year at present. The capacity of the coalfired power plants is 93% in the total thermal power plants. Increased coal consumption in large coal fired power plants and cities implies increased thermal pollution, particulate release (smog), sulfur emission, acid rain, greenhouse effect and hazardous trace elements emission.
When coals are mined and stored, most of hazardous trace elements in coal will be leached out and enter into water, soil environments . During beneficiation and the reduction in traceelement levels in the clean coal, there is an associated increase in traceelement contents in the reject material and washery water. The disposal of these washery rejects must be undertaken carefully because their increased contents of pyrite and others hazardous trace elements are a potential source of acidic solutions that could contaminate local waters with increased concentrations of trace elements.
During coal burning, the trace elements in coal will move or transform into following aspects: the first is that they volatilize out into air with smoking in forms of gas; the second is that they consist in fly ash or powder dust and other little matters and get into the air in forms of solid granule ; the third is that parts of them still reserve in coalashes . So when coal is used as fuel , not only do COx , NOx and SOx give out into atmosphere and form acid rain , but also do many hazardous trace elements volatile out in the forms of aerosols and gaseous products of smoke and fine particles and migrate in air , at last they will get into soil and water under function of rainfall . Most of hazardous trace elements will be volatilized out from coal (coal gangue and ashes) when coal is burnt. They will volatile into atmosphere in the forms of gas, aerosols and fine particles and into water with leaching solution , and recycle among air, water, soil and the living , at last, they do harm to human health.
Trace elements in coal are important because of their association with environmental issues and the health of plants, animals and humankind. Consideration must be given to essentiality, nonessentiality and toxicity that depend on concentrations, the form of the element, pH and oxidationreduction conditions and other factors. During process of coal formation, which began from plants growing to peat swamp and to types of coal rank, there were many factors of influence upon migration and concentration of minor elements. The factors mainly include plant types , chemical conditions, climate conditions , sea water aggression, magma hydrotherm fluid effect during coalification and matter exchange between coal and rocks of roof and floor. So the formation and concentration of minor elements in coal is the systhesizal results of many geological factors during coalification stages. The modes of occurrences of trace elements in coals control toxicity and giving off degree of difficulty of trace elements during coal utilizing and processing. It is very important to study on modes of occurrences of trace elements in coals for detail evaluating artistic characters, affecting environment, regarding as productions and using in geology. In this paper, on the basis of the research on data in the world, the history and developments of the study on the found, occurrence, formation of trace elements in coal are analyzed in detail. The important content and direction is environmental geochemistry in the future.