稀土元素在煤燃烧过程中形态演变规律模拟研究

Evolvement Law of Occurrence of Rare Earth Elements During Coal Combustion

针对目前煤和粉煤灰中稀土元素赋存状态关系不明确的问题,研究煤系稀土元素赋存状态在燃烧过程中的转化行为具有重要意义。选取煤系稀土赋存的模型矿物,通过滴管炉进行模拟燃烧,采用热重分析、XRD分析、SEM-EDS和逐级化学提取探究不同赋存形态稀土的演变规律,结果表明:以独居石为代表的磷酸盐稀土资源在燃烧过程中化学性质并未改变,仅粒度减小;以氟碳铈矿为代表的碳酸盐稀土资源在燃烧过程(350~580℃)发生分解和氧化反应,转化为铈的氧化物和氟化物,其中的稀土元素更易在温和条件下浸出;以离子型稀土矿为代表的黏土矿物中稀土资源根据燃烧温度可以两种状态,800℃时,石英和长石等存在其中,高岭石等发生脱氢反应,产物呈碎屑状、无规则状,逐级化学提取中稀土元素浸出率提高,1200℃,石英存在,铝硅酸盐矿物主要转化为莫来石,颗粒呈现球状和片状,不利于稀土元素浸出;以改性褐煤(通过离子吸附负载铈)为代表的有机质中稀土资源,燃烧后离子态的铈变成了铈的氧化物。

The relationship of occurrence of rare earth elements(REE)in coal and coal ash is not clear now so that it is significant to study the transformation of REE occurrence during coal combustion.This paper intends to investigate the evolvement law of REE occurrence via TGA-DSC and XRD analysis,SEM-EDS,and sequential chemical extraction(SCE)applied for model minerals and their combustion products by drop tube furnace.The conclusions are shown in the following.Monazite,as the proxy of REE resources in phosphate,is still monazite of which particle size only decreases.Bastnaesite,as the proxy of REE resources in carbonates,decomposed at 350~580℃and produced the oxide and fluoride of Ce.Cerium is easily leached by SCE in the product than bastnaesite.Ion-adsorption type REE mineral,as the proxy of REE resources in clay,has higher leachability of REE by SCE after 800℃combustion.Quartz and feldspar are still in the product and dehydro-kaolinite appears.However,the REE leachablity decreased after combusted at 1200℃due to the vitrification of aluminosilicate.The product contains mullite and quartz.Lignite coal absorbed Ce^(3+),as the proxy of REE resources in the organics,was combusted and the oxide of Ce was found in the product.