臭氧微气泡氧化三价砷形成臭葱石沉淀除砷方法的研究

A great deal of toxic arsenic bearing wastes is produced in hydrometallurgy plants of China, which cannot be treated safely and economically. Solidification and stabilization are currently considered as the best treament of arsenous wastes. Scorodite is accepted as the best compound for arsenic disposal for its low solubility and high chemical stability. However, scorodite has to be formed in autoclave under high pressure and cannot be applied widely. Some research showed that scorodite formation can be realized at atmospheric pressure with the addition of crystal seeds by a reaction between As(V) and Fe(III). Aimed at the fact that As(III) is very hard to be oxidized to As(V) under acidic condition at atmospheric pressure, in this project, ozone microbubble is proposed to be used to oxidize As(III) for its high oxidizing power, so the formation of scorodite can be realized by adjusting the rate of As(III) oxidizing. The characteristics of reaction and mass transfer of ozone microbubbles in the heavy metal salts solution with high concentrations will be investigated. The kinetic rate constants and transfer rate constants will be measured under different ion concentrations and the rate controlling step will be determined. The process of scorodite crystalization will be monitored online, the rate of As(III) oxidizing on the nuclearation will be disscussed and the influence of the microbubbles on growth of the crystal particles will be investigated. Finally, based on this study, a technical prototype of scorodite formation at atmospheric pressure will be proposed and the operating conditions will be established.

我国有色冶金工业每年产出大量的剧毒含砷废弃物，目前尚缺乏安全有效的处理手段。实现砷的固定化和稳定化，被公认为是目前最佳的砷处理方式，臭葱石(FeAsO42H2O)结晶因为性质稳定被认为是最适合的固砷化合物。但是现有臭葱石的生产必须采用高压条件，成本高、难以推广应用。已有研究表明：常压下可以由五价砷与三价铁在晶种诱导的情况下合成臭葱石晶体。本项目针对常压酸性条件下三价砷难以氧化的问题，提出采用臭氧微气泡强化氧化过程，通过控制三价砷的氧化速度来实现臭葱石的常压制取，并对臭氧微气泡在高浓度重金属溶液这一特殊条件下的反应和传质特性进行研究，测定不同离子和不同离子浓度下臭氧微气泡氧化三价砷的反应动力学和传质速率常数，确定反应的控制步骤；探讨三价砷氧化速度对成核过程的影响规律，考察微气泡对臭葱石晶体生长动力学的影响。最终给出新的常压下臭葱石除砷净化工艺的反应操作条件和技术原型。

我国有色冶金工业每年产出大量的剧毒含砷废弃物，目前尚缺乏安全有效的处理手段。臭葱石(FeAsO42H2O)结晶因为性质稳定被认为是最适合的固砷化合物。但是现有臭葱石的生产必须采用高压条件，成本高、难以推广应用。本项目详细研究了常压臭葱石除砷方法，并提出了常压臭葱石除砷技术原形。首先研究了酸性条件下臭氧氧化三价砷过程，结果显示与空气相比，臭氧能够快速氧化三价砷，在pH1-5范围内，氧化速度随pH上升而升高。在23—53℃，氧化速度随温度上升而减慢；其次研究了臭葱石结晶反应动力学，结果发现提高二价铁氧化速率和初始pH，可以促进砷沉淀，另一方面，实验结果表明添加三价铁离子会导致在加热过程中形成无定形砷酸铁，但生成的无定形砷酸铁可以转化为臭葱石。最终提出了一个两段法用于废水除砷，在此过程中首先在pH 2条件下通过空气氧化二价铁与砷形成臭葱石沉淀，然后提高pH至3-4，使残余的砷吸附到无定形水铁矿上彻底去除。TCLP浸出毒性测试证明产生的沉淀产物是稳定的。