石灰-铁盐法除砷工艺及其在工业含砷酸性废水处理中的应用

Technology of arsenic removal with lime-iron salt process and its application in treatment of industrial arsenic-bearing acidic wastewater

石灰-铁盐法常用于含砷酸性废水的处理,具有投加药剂种类少、沉淀效率高、废水排放稳定达标、运行费用低、操作方便等优点,本文对该方法的反应机理和影响因素进行了阐述,并对工艺进行了总结。反应液pH值设定为7~8时,Fe^(2+)氧化反应效率高,除砷效果最佳;反应液Fe/As物质的量比一般为5~10,有利于砷酸铁的形成,同时可促进絮凝过程;采用沉渣部分回流法可以为反应过程起到晶核作用,不但能提高中和渣的沉降速度,还能节省药剂、减小中和渣体积。工程实践表明该方法可高效处理铜冶炼厂产生的含砷酸性废水,Cu、Pb、Zn以及As的去除率均可稳定达到99%以上,而且中和渣中As以五价砷酸盐存在,其毒性浸出浓度小于5 mg/L,可安全堆存于渣库内。

The lime-iron salt process is usually used in the treatment of arsenic-bearing acidic wastewater,and it has the advantages of fewer kinds of reagent to be added,high precipitation efficiency,stable and qualified discharge of wastewater,low running cost,easy operation,etc.In this paper,the reaction mechanism and influence factors of this process are elaborated and summary is made for this process.When the pH value of the reaction liquid is set as 7-8,the oxidizing reaction of Fe^(2+) is high with the best arsenic removal effect;the molar ratio of Fe/As of the reaction liquid is generally 5-10,which is conducive to iron arsenate formation and accelerates flocculation;the partial sediment returning method adopted can play a role of crystal nucleus for the reaction process;in this way,not only the precipitation velocity of the neutralized residue can be raised,but also the reagents can be saved with the volume of neutralized residue reduced.The engineering practice shows that this process can efficiently treat the arsenicbearing acidic wastewater from copper smelter,the efficiency for removing Cu,Pb,Zn and As can be stably up to 99%or more.In addition,the As in the neutralized residue is in form of pentavalent arsenate and the concentration of toxic leaching is less than 5 mg/L,which can be safely stored in residue pond.