【作者】 李莉；

【导师】 李启厚；

【作者基本信息】 中南大学 ， 有色金属冶金， 2009， 硕士

【摘要】 砷是有色金属矿产中一种常见的伴生元素,而含砷化合物中,As³⁺的毒性和移动性均远远超过As⁵⁺,因此As³⁺的氧化成为常规除砷过程中必不可少的处理步骤。以往探索三价砷氧化过程,多处理的是酸性体系,而对碱性体系探讨不足。本文研究的是碱性环境中三价砷的空气氧化过程,讨论了不同试剂对该过程的催化效应,确定了高锰酸钾试剂对反应具有显著的促进作用。实验考察了溶液pH值、总砷浓度、空气流量、反应温度等因素对三价砷氧化速率的影响,并采用X射线衍射、扫描电镜、化学物相分析等方法对反应产物进行了表征。结果表明:高锰酸钾在和三价砷的反应过程中具备超计量氧化的特点,在体系As/Mn摩尔比升至21:1时仍能高效地将As³⁺氧化,其对空气氧化过程的促进作用主要表现在:高锰酸钾直接氧化As³⁺;体系有空气通入的情况下,锰离子或锰氧化物可表现出一定的催化作用;高锰酸钾反应产物K_0.27MnO₂（H₂O）_0.54对As³⁺存在较强的吸附作用,可促进As³⁺的催化氧化过程。锰-砷反应过程存在着两种反应速率,初始反应速率极快,而后变缓,这主要受反应机理以及反应物、反应产物的扩散过程控制。体系pH值通过影响产物性质而对氧化效果有显著的影响,体系初始pH=12.5～13范围内反应将生成富钾新生态二氧化锰K_0.27MNO₂（H₂O）_0.54;初始pH=12时反应产物以液态存在;最适宜的体系pH值为13。体系总砷浓度升高可影响固体产物形貌,同时减慢氧化速率,最适宜的总砷浓度为0.0667～0.2002mol/L,其中总砷浓度为0.0667mol/L时,反应2h即可完全氧化体系中的As³⁺。增加体系空气流量或者升高温度会显著加快As³⁺的氧化速率,最适宜的气流量为0.2m³/h,最佳的反应温度为80℃。以高锰酸钾作催化剂,空气氧化三价砷,具有试剂用量少、操作简单、氧化效率高等优点,具备良好的工业应用前景。更多还原

【Abstract】 Arsenic is a ubiquitous associated element in nonferrous metallic minerals, As³⁺ is more toxic than As⁵⁺, thus the oxidation of As³⁺ is an absolutely necessary process in normal arsenic-removing process. Former researches on arsenic oxidation were mainly dealing with acidic system, and few achievements had been made in alkaline system. In this article, the arsenic air oxidation process was systematically studied in basic system. Analyzed and compared the catalytic effects of different catalysts, potassium permanganate was confirmed the most effective catalyst in this system. Influences of experimental conditions on arsenic oxidation rates were also discussed, such as solution pH value, arsenic concentration, air flow and reaction temperature. Reaction products were characterized by x-ray diffraction analysis, SEM paragraph analysis and chemical phase analysis.The results showed that potassium permanganate could oxidize far more arsenic than simply calculated from chemical reaction equations, As³⁺ were effectively oxidized when system As/Mn molar ratio exceeded 21:1. Potassium permanganate could promote As³⁺ oxidation by the following mechanisms: potassium permanganate directly oxidized As³⁺; manganese ions or manganese compounds could catalyze the air oxidation process; potassium permanganate reacted product K_0.27MnO₂（H₂O）_0.54 could adsorb As³⁺, thus promoting the catalytic oxidation process. There existed two different reaction rates in Mn-As reaction process, the fast reaction rate in the beginning would slow down when reaction progressed for about 30min, controlled by variations in reaction mechanism and diffusion process. The system pH values could significantly influence oxidation effects by changing product properties, K_0.27MnO₂（H₂O）_0.54 which belongs to potassium-richδ-MnO₂ would be produced when initial system pH values were 12.5～13, however liquid manganese product would be produced when initial pH changed to 12. The increase in arsenic concentration would influence product morphology and decelerate reaction rates, the optimum As concentrations were 0.0667～0.2002mol/L. It took 2h for the complete oxidation of As³⁺ when C_As=0.0667mol/L. The increase in air flow or temperature would accelerate As³⁺ oxidation, and the optimum conditions were 0.2m³/h and 80℃.Taking potassium permanganate as catalyst, the air catalization oxidation process of arsenic has the advantages as little reagent dosage, easy operation and high oxidation efficiency, thus it has wide application prospect in industry.更多还原