三段石灰法处理重金属酸性废水的工艺改进

Process improvement of sulfuric acid containing heavy metal ion treated by three—stage lime

通过实验对三段石灰法处理重金属硫酸废水的工艺进行了改进,提出石灰消化时间由原来的4 h延长到24 h以上,一段硫酸废水混凝反应的p H由原来的3~5变为10~11,弃用一段沉淀污泥回流;二段处理把原工艺采用石灰乳调节p H改用氢氧化钠和磷肥厂的磷酸废水,出水p H控制在8~9;二段出水过滤设备把原来纤维球过滤装置改为砂滤,砂滤出水回用于工艺,滤料反冲洗采用硫酸废水,清洗采用清水池循环水。实验表明：通过改进,出水中Zn2＋,Pb2＋,Cd2＋,Cu2＋浓度小于1.0 mg/L,废水中重金属达标排放,同时大大降低了出水中Ca2＋浓度,缓解了出水循环利用工艺严重结垢问题,也解决了原工艺处理出水p H高形成较高浓度重金属配合物污染土壤河流问题。

The process of treating acidic wastewater containing heavy metals by three - stage lime is improved by small - scale test. The results show that the time of lime digestion is extended from 4 h to 24 hour. pH of flocculation reaction may change from the original 3 - 5 into 10 - 11 in first stage. Precipitation back -flow is not adopted. The pH is adjusted to adopting phosphoric acid wastewater and sodium hydroxide and the pH of effluent in the second stage is controlled within 8 and 9. Filter equipment with fiberball replaced with sand filter. The effluent is reused to process. Acidic wastewater is used to backwashing of filter and recycled water is used for cleaning. The results show that the concentrations of Zn^2＋ , Pb^2＋ , Cd^2＋ and Cu^2＋ ion less than 1.0 mg/L, which meet effluent standard, and the concentration of Ca^2＋ ion is reduced remarkably in effluent. The problem of serious scaling is solved and the problem of soil pollution resulted from high concentration heavy metal clathrate is solved as well.