Environmental Geochemistry Of Antimony In Chinese Coals And Two Typical Mines

Antimony (Sb) is a trace element in the Earth's crust. Significant quantities of Sb are used by several industries in modern times. The toxicity of Sb compounds in the environment has been increasingly recognized recently. Sb is commonly enriched in practically all metal sulfide ores (especially those of Pb and Cu) as well as in coal. Major anthropogenic sources of Sb are fossil fuel combustion, non-ferrous metals refining, waste incineration, and incineration of sewage sludge. Coal is one of the most important sources of energy. Its worldwide use will continue to expand during next several decades, particularly in rapidly developing countries, including China. There is an urgency to enhance the knowledge of Sb in coals and related deposit.The distribution, modes of occurrence, geological processes and environmental effect of Sb in Chinese coals has been reviewed.1458 coal samples were collected from Chinese sources and the average Sb content in Chinese coals is 3.68μg g-1. Based on average Sb content, coal from provinces, cities and autonomous regions may be divided into three groups. Sb is extremely enriched in the Guizhou and Inner Mongolia Coals. The amount of Sb in coal varies with coal-forming periods and coal ranks. Environmental impact of a trace element in coal is related to its concentration and modes of occurrence. There are several modes of occurrence of Sb in coal. It occurs in discrete pyrite grains and is dispersed in the organic matter as tiny sulfide particles. During coal combustion Sb is partly released to the atmosphere and partly partitioned into the solid residues. Sb in the environment brings about definite harm to human health. The forms of Sb in five selected coals were studied by sequential solvent extraction. Results show that the silicate-bound Sb is the most abundant form in these coals. Silicate plus sulfide-bound Sb accounts for more than half of the total Sb in all coals. Bituminous coals are higher in organic matter-bound Sb than anthracite and natural coke, indicating that the Sb in the organic matter may be incorporated into silicate and sulfide minerals during metamorphism. Thirty-three soil samples were collected from the Luling, Liuer, and Zhangji coal mines, in the Huaibei and Huainan areas, Anhui Province, China. The average Sb content in 33 samples was 4.0μg g-1, which is lower than that recorded in coals from this region (6.2μg g-1). More than 75% of the soils sampled show a significant degree of Sb pollution (EFs 5-20). The soils collected near the gob pile and coal preparation plant were higher in Sb content than those collected from residential areas near the mines. The gob pile and tailings from the preparation plant were high in mineral matter content and high in Sb. They are the sources of Sb pollution in surface soils in the vicinity of coal mines. The spatial dispersion of Sb in surface soil in the mine region shows that Sb pollution could reach out as far as 350 m. Crops in rice paddies may adsorb some Sb and reduce the Sb content in soils from paddy fields. Vertical distribution of Sb in two soil profiles indicates that Sb is relatively immobile in soils. Sb distribution and accumulation in plants in Xikuangshan Sb deposit area, the only super-large Sb deposit in the world, Hunan, China, were investigated. Results show that soils were severely polluted with the average Sb concentrations up to 5949.20μg g-1. Sb widely occurred in 34 plants with various concentrations ranging from 3.92μg g-1 to 143.69μg g-1. Bioavailability of Sb was limited and varied with different soil types (sites) as well as plant species. Equisetaceae family has the highest concentration (98.23μg g-1) while Dryopteridacea family has the lowest one (6.43μg g-1). H. ramosissima species of Equisetaceae family had the highest average Sb concentration of 98.23μg g-1 and P. vittata species of Pteridaceae family showed high abilities of accumulating Sb from the contaminated environment (Biological Accumulation Coefficient, BAC=0.08). Almost all species enriched Sb in their upground part such as shoot, leaf and flower (Biological Transfer Coefficient, BTC>1). P. phaseoloides and D. indicum showed predominant accumulation of Sb in the upground part with BTC of 6.65 and 5.47, respectively. Those observations would be significant to the phytoaccumulation and phytoremediation of Sb in plants and ecological and environmental risk assessment of Sb in contaminated areas.