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Transformation of arsenic in Yima coal during fluidized-bed pyrolysis

机译：流化床热解过程中义马煤中砷的转化。

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摘要

Arsenic is one of the most concerned trace elements in coal because of its toxicity and environmental persistence. Little information about the transformation behavior of arsenic under pyrolysis conditions was reported. In this paper, the volatilization behavior of arsenic and the influence of coexisting mineral matters and additive CaO were investigated during pyrolysis of Yima coal in a fluidized-bed reactor at temperatures ranging from 350 to 900℃. The modes of occurrence of arsenic in Yima raw coal and its two char samples are determined using four methods including density fractionation, demineralization, X-ray diffraction (XRD) and sequential chemical extraction. It is found that arsenic in Yima coal is mainly associated with pyrite, and changes greatly during coal pyrolysis. Staged volatility behavior of arsenic is observed during Yima coal pyrolysis. From 350 to 500℃, arsenic volatility increases with increasing temperature, while it changes little from 500 to 800℃. Arsenic behavior in YimaD (demineralized sample of Yima) and CaO additive reveal that the vaporization of arsenic in Yima coal during pyrolysis is retarded by its coexisting mineral matters or added CaO to form thermally stable forms of arsenic. These forms might be generated through the formation of As-Ca complexes such as calcium arsenate, or through absorption and capture reactions with aluminosilicate mineral matters and trapped into their lattices.
机译：砷是煤中最受关注的微量元素之一，因为它具有毒性和对环境的持久性。关于热解条件下砷的转化行为的报道很少。本文研究了伊马煤在350-900℃温度下的热解过程中砷的挥发行为以及矿物质和添加剂CaO共存的影响。义马原煤及其两个焦炭样品中砷的发生方式采用密度分级，脱矿质，X射线衍射（XRD）和顺序化学萃取四种方法确定。研究发现，义马煤中的砷主要与黄铁矿有关，并且在煤热解过程中变化很大。在义马煤热解过程中观察到砷的分阶段挥发性行为。从350到500℃，砷的挥发性随温度的升高而增加，而从500到800℃变化不大。 YimaD（Yima脱矿质样品）和CaO添加剂中的砷行为表明，Yima煤在热解过程中的砷汽化受其共存的矿物质或添加CaO形成热稳定形式的砷的阻碍。这些形式可能是通过形成砷化钙复合物（例如砷酸钙），或通过与铝硅酸盐矿物质的吸收和捕获反应而生成的，并被捕获在其晶格中而产生的。

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