铁岭煤中重金属元素的赋存形态及其在热解过程中的挥发行为研究

OCCURRENCES OF TRACE METALS IN TIELING COAL AND THEIR VOLATILITY BEHAVIORS DURING PYROLYSIS

采用密度分离、脱灰处理和逐级化学提取等间接方法,考察了铁岭煤中Pb,Cr,Co,Ni,V五个重金属元素的宏观结合形态,并在Φ25mm小型石英流化床反应装置上考察了上述五个重金属元素在热解过程中的挥发行为。研究发现,铁岭煤中Pb,Cr,Co,Ni,V均主要与非黄铁矿类矿物质相伴生,且高达40%～60%赋存在硅酸盐类矿物质中。Pb的碳酸盐结合态和有机束缚的离子可交换态600℃前即可分解转化,而其硫化物和硫酸盐结合态在较高的热解温度下才能分解挥发;Co、Ni的硫化物和硫酸盐结合态在高温下可部分转换为有机结合的离子可交换态;而Cr、V的硫化物和硫酸盐结合态在高温下部分转化生成了新的热稳定相。在500℃～900℃范围内,Pb属半挥发性元素,Cr,Co,Ni,V属难挥发性元素。微量元素的挥发性极大地受其伴生环境、共存活泼元素等的影响,硅铝酸盐类矿物质对重金属元素的挥发有一定的抑制作用。

Modes of occurrence of Pb, Cr, Co, Ni, V in Tieling raw coal and two char samples were determinedusing density fractionation, demineralization and sequential chemical extraction methods. Volatilization behaviors of Pb, Cr, Co, Ni and V were investigated during pyrolysis of Tieling coal in a fluidized-bed reactor at temperatures ranging from 500?℃ to 900?℃. Pb, Cr, Co, Ni, V in Tieling coal are mainly associated with mineral matters such as silicates, sulfates, sulfides, and about 40%～60% of them are associated with alumino-silicate mineral matters. Lead associated with carbonates and organic bonded ion exchangeable forms has already decomposed below 600?℃. Forms of Pb, Cr, Co, Ni, V associated with sulfates and sulfides are unstable, whereas the transformation behaviors of them are different. Thermally stable phases of Cr and V are formed under high pyrolysis temperatures. In the temperature range studied, Pb belongs to semi-volatile elements, while Cr, Co, Ni and V belong to non-volatile elements.