CaCl2-PAC工艺处理酸性高氟废水

以湖南某氟化盐厂排放的酸性高氟废水为研究对象,提出CaCl2-PAC处理酸性高氟废水新工艺,确定了最佳工艺条件,并对比了晶种添加前后对除氟效果、沉渣含水率的影响及沉渣中氟化钙的纯度;结果表明:在钙盐沉淀阶段, pH≈9, n (Ca/F)=0.75,搅拌45 min、沉降90 min;在絮凝沉淀阶段,pH≈7.5,PAC投加量为350 mg/L,最后出水氟离子浓度可降至10 mg/L以下,达到了《污水综合排放标准(GB8978-1996)》的一级标准。在钙盐沉淀阶段按照10 g/L添加大颗粒氟化钙后,氟去除率进一步提高,处理后所得的沉渣氟化钙纯度可达到85%,沉渣含水率较晶种添加前降低20%,有利于实现高效除氟和氟化钙的回收利用。

Treatment of acidic and highly concentrated fluoride wastewater using calcium chloride-poly aluminum chloride

A new removal process by using calcium chloride together with poly aluminum chloride (PAC) was reported for the treatment of the acidic and highly concentrated fluoride wastewater which was discharged from a fluoride salt plant in Hunan.The optimum process conditions were determined.Compatative studies were carried out on the fluoride-removal effect as well as the moisture content and the CaF2 purity of the sediment,with or without adding the seed crystal of CaF2.Results showed that (i) in the first stage of precipitation with calcium salt,the optimum conditions were as follows:the pH was adjusted around 9 using a calcium hydroxide solution,and the dosage of the 5% calcium chloride solution was determined according to the mole number of CaF2 (herein,n=0.75),stirring for 45 min and precipitating for 90 min,and then (ii) in the second stage of flocculation with PAC,the optimum conditions were as follows:the pH was around 7.5 and the dosage of PAC was 350 mg/L.Then,the residual mass concentration of fluoride ion in the wastewater could be controlled under 10 mg/L,meeting the first class of Integrated Wastewater Discharge Standard (GB-8978-1996).Besides,in the first stage by adding the seed crystal of CaF2 with a dosage of 10 g/L,in the sediment the moisture content was found to decrease by 20% while the CaF2 purity increased up to 85%,which indicates a better fluoride-removal effect and benefits for CaF2 recovery and reuse.