在分析石灰铁盐法含砷石膏渣的物相组成和浸出毒性基础上,开展石膏渣-煤粉的TG-DSC和固-固反应研究,探索石膏渣碳热还原分解行为及砷迁移规律.结果表明:石膏渣在1000℃时的质量损失率接近50％,石膏渣与煤粉质量比为40∶1时能够有效促进热分解,具有较高的质量损失率;石膏渣-煤粉反应过程中,分解残渣出现CaSO4→CaS→CaO的物相转变,还原分解后期CaSO4→CaO/SO2转变较为彻底,挥发率为45.29％、减容率为65.83％,气体产物成分为SO2和CO2,挥发性烟尘丰要成分为As2O3;分解残渣微观结构较为致密,砷浸出毒性为1.05mg/L低于《GB 5085.1--2007》限值,浸出率仅为原石膏渣的1/236,残留的63.38％砷被有效固化在分解残渣中.碳热还原分解实现石膏渣的无害化处置、硫资源利用和砷的富集.
On the basis of chemical composition,phase,leaching toxicity and thermal stability of arsenic bearing gypsum sludge obtained in lime/ferrous sulfate precipitation process,the reductive decomposition characteristics and arsenic migration rule were investigated by TG-DSC and solid-solid reaction between arsenic bearing gypsum sludge and coal.The results show that mass loss ratio of 50％ is obtained when temperature reaches to 1000 ℃.A sludge/coal mass ratio of 40∶1 can effectively promote the thermal decomposition and lead to a higher mass loss rate.The CaSO4→CaS→CaO phase transformation occurs during the reductive decomposition process of gypsum sludge/coal.The transformation of CaSO4→CaO/SO2 proceeds completely and a volatilization rate of 45.29％ and a volume reduction rate of 65.83％ are obtained in the final stage.The evolved gas is consistent with SO2 and CO2 while AS2O3 is the main phase of dust.The reacted residue is characterized with dense structure.The arsenic concentration in leaching toxicity test of the reacted residue is 1.05 mg/L which is lower than limit in GB 5085.1-2007.It is found that 63.38％ of total arsenic remained in the reacted residue but with a low arsenic leaching rate (1/236 of arsenic leaching rate in gypsum sludge).The reductive decomposition of arsenic bearing gypsum sludge realizes the harmless disposal,sulphur utilization and arsenic enrichment.
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