褐煤粉煤灰中污染物砷的真空硫化脱除机理及锗的还原提取

In Yunnan and Inner Mongolia (China), a large amount of coal fly ash is produced in the process of incineration power generation of lignite. The coal fly ash not only contains toxic pollutants but also rare metals of germanium. In this study, to achieve the removal of arsenic and the extraction of germanium in coal fly ash, separation process based on vacuum sulfuration and reduction characteristics of arsenic and germanium in coal fly ash and the difference of evaporation characteristics of their products under vacuum have been proposed. Firstly, the thermodynamics of vacuum sulfuration reaction in coal fly ash and the kinetics of product evaporation separation are studied to determine the type of sulfide product and the removal of arsenic. The vacuum migration, transformation of sulfide products and the removal mechanism of arsenic are revealed. In turns of the extraction of germanium in the coal fly ash by vacuum reduction, the thermodynamic mechanism of vacuum carbon reduction reaction of germanium and the mechanism of carrier airflow on the formation, evaporation and condensation of metallic germanium molecules are revealed. The molecular dynamics model of molecular evaporation and condensation of germanium are established. Finally, based on the chemical morphological changes of arsenic and germanium in the reaction, the crystal structure transformation, and the chemical composition analysis of the product, the theoretical criterion for the vacuum separation of arsenic and germanium are established with the calculation of the thermodynamic equilibrium simulation of the reaction, the density functional function of electron migration and the calculation of evaporation kinetics. This research aims to solve the key theoretical problems in the reaction, separation, and extraction of arsenic and germanium under vacuum condition. And this would provide a theoretical basis for the development of detoxification of coal fly ash and move current technology towards a green, efficient and low-cost recovery of valuable resource.

我国云南、内蒙等地的褐煤在焚烧发电过程中产生了大量的粉煤灰，这些粉煤灰既存在有毒污染物砷又含有稀散金属锗。本研究提出利用粉煤灰中砷、锗的真空硫化和还原特性及产物真空蒸发性质的差异，实现砷的脱除和金属锗的提取。首先，研究粉煤灰中砷的真空硫化反应热力学及产物蒸发分离动力学过程，确定砷硫化产物类型和砷脱除的影响，揭示砷硫化产物的真空迁移转化规律及脱除机理。然后，通过真空还原提取粉煤灰中锗，阐明锗的真空碳还原反应热力学过程，载气流对金属锗分子生成、蒸发与冷凝分离作用机制，建立锗分子蒸发和冷凝过程分子动力学模型。最后，结合反应中砷、锗化学形态变化、晶体结构转变和产物化学组分分析，通过反应热力学平衡模拟、电子迁移的密度泛函数及蒸发动力学计算，建立砷、锗真空分离的理论判据。研究旨在解决真空下砷、锗反应和分离提取过程中的关键理论问题，为开发粉煤灰的解毒，有价资源绿色、高效、低成本回收关键技术提供理论基础。

在实现我国可持续发展的过程中，废弃资源高效循环利用是关系到国计民生的重要课题。粉煤灰是煤炭在燃煤电厂锅炉中燃烧后产生的固体废渣，是我国目前最大的单一固体污染源。在云南、内蒙等地采用褐煤焚烧发电来利用其中的能源，褐煤中的有毒元素砷在高温焚烧过程中以砷氧化物和砷化物形式挥发、气化，并富集于细小的粉煤灰中。除了有毒元素砷外，褐煤粉煤灰中还含有约0.1%-0.3%的稀散金属锗。目前，对褐煤粉煤灰中锗的分离方法仍采用传统湿法冶金技术，即在酸性或碱性溶液中，通过化学试剂的氧化和络合等作用，将金属锗转化成水溶性离子，再通过化学沉淀、离子交换、萃取、吸附等还原方式实现锗的分离和提取。本研究基于褐煤粉煤灰中砷、锗在真空条件下所具有的不同反应特性及其产物蒸发性质等物理化学特性差异，提出了真空下褐煤粉煤灰中砷的硫化脱除和稀散金属锗的还原提取新方法。通过一系列实验，验证了在最佳条件下砷的去除以及锗和钨的富集。结果表明，在550℃的反应温度下，加入50 wt.%的硫化剂，系统压力为1Pa，反应时间为240 min，As的去除率为96±1%，Ge和W的含量分别为0.75±0.023 wt.%和0.24±0.016 wt.%。EDS光谱显示S和As的含量分别为99.56 wt.%和0.41 wt.%。这表明冷凝管远端的冷凝产物主要是硫磺粉和少量砷。在蒸发过程中，砷以As2S3和As4S4的形式蒸发。我们提出了从煤灰中释放砷、真空硫化、蒸发和冷凝的潜在机制。两级反应系列模型（1-（1-α）2）在这些动力学机制函数中具有最佳拟合。拟合度（r2）可达0.995，表明反应系列的动力学机理函数符合砷氧化物的硫化反应。可以计算出表观活化能（Eα）为31.24KJ mol-1。对锗的真空还原过程，温度为920.53 oC，压力为259.63 Pa，还原剂用量为16.64 wt.%，锗的分离率为93.35%。通过GeO2的还原反应制备纯金属锗。还原反应炉为无氧炉，炉内瓷舟为无盖瓷舟。反应条件是将制备的纯GeO2与10 wt. % 焦炭作为还原剂，温度为 800 oC，反应时间为 40 min。生成的金属锗呈气相，在高温下充满于炉内。通过ICP-AES测量，锗的纯度为98.12 ± 0.54 %。