“扩散渗析+三步沉淀”组合法资源化处理不锈钢酸洗废水

Recycling Treatment of Stainless Steel Pickling Wastewater by Combination of Diffusion Dialysis and Three-step Precipitation Processes

摘要

我国是全球最大的不锈钢生产国, 不锈钢生产过程会产生大量的酸洗废水, 包含高浓度的强酸和重金属盐, 若直接排放会严重污染环境, 且造成资源浪费. 本文采用“扩散渗析+三步沉淀”组合法对不锈钢酸洗废水进行资源化处理. 首先, 采用扩散渗析过程将废水中的高浓度混酸(包括硝酸和氢氟酸)与废水中的重金属盐(包括铁、铬、镍重金属盐)进行分离以回收混酸; 之后采用三步沉淀过程对扩散渗析残液中的重金属(包括铁、铬和镍)进行回收; 并考察了离子交换膜种类、废水进料流量及扩散侧/渗析侧流量比对扩散渗析过程混酸回收率和重金属截留率的影响, 同时优化了三步沉淀工艺(沉淀剂组成、沉淀温度和pH值等). 结果表明, 扩散渗析的最佳工艺为: 采用TWDDA3S型阴离子交换膜, 废水进料流量为6 mL/min, 扩散侧与渗析侧流量比为1.5∶1. 在此条件下, 硝酸与氢氟酸的总回收率最高可达69.5%, 同时铁、铬和镍3种重金属离子的截留率分别达到97.0%, 98.0%和96.4%; 第一步沉淀的最佳工艺为: 复合沉淀剂组成为c(KOH)∶c(KF)=7∶1, 沉淀温度为15 ℃, 在此条件下重金属铁和铬的回收率分别达到96.2%和90.7%; 第二步沉淀的最佳工艺为: 采用0.02 mol/L HNO₃和0.30 mol/L KF对第一步沉淀滤液进行深度处理, 在此条件下镍离子的保留率和纯度分别达98.7%和89.6%; 第三步沉淀的最佳工艺为: 通过KOH将滤液pH值控制在11左右, 在此条件下可实现镍的全部回收.

Abstract

China is the largest producer of stainless steel in the world. The production process of stainless steel generates a large amount of pickling wastewater, which contains high concentrations of strong acids and heavy metal salts. If discharged directly, it will seriously pollute the environment and cause resource waste. Therefore, this study designs a combined method of "diffusion dialysis + three-step precipitation" for the recycling treatment of stainless steel pickling wastewater. Firstly, the diffusion dialysis technology was adopted to separate the high-concentration mixed acids (including HNO₃ and HF) from the heavy metal salts (including iron, chromium, and nickel heavy metal salts) in the wastewater to recover the mixed acids. Subsequently, a three-step precipitation method was used to recover heavy metals (including iron, chromium, and nickel) from the residual liquid of diffusion dialysis. The influence of ion-exchange membrane type, feed flow of the wastewater and the flow ratio of the diffusion side to the dialysis side were investigated on both the mixed acid recovery rate and heavy metal retention rate in the diffusion dialysis process. Meanwhile, the three-step precipitation technics was optimized (including the precipitant composition, precipitation temperature and pH value, etc). The research results showed that the optimal process for diffusion dialysis is: TWDDA3S anion exchange membrane was adopted, the feed flow of wastewater was 6 mL/min, and the flow ratio of the diffusion side to the dialysis side was 1.5∶1. Under these conditions, the total recovery rate of nitric acid and hydrofluoric acid could reach up to 69.5%. Meanwhile, the retention rates of the three heavy metal ions including iron, chromium and nickel reached 97.0%, 98.0% and 96.4%, respectively. The optimal process for the first-step precipitation is as follows: the mole concentration ratio of the composited precipitants of KOH and KF is 7∶1, and the precipitation temperature is 15 ℃. Under these conditions, the recovery rates of heavy metals of iron and chromium reach 96.2% and 90.7%, respectively. The optimal process for the second-step precipitation is as follows: 0.02 mol/L HNO₃ and 0.30 mol/L KF are used to conduct advanced treatment on the filtrate from the first-step precipitation. Under these conditions, the retention rate and purity of nickel ions reach 98.7% and 89.6%, respectively. The optimal process for the third-step sedimentation is to control the pH value of the filtrate at around 11 with KOH, under which all nickel could be recovered.

关键词

不锈钢酸洗废水 / 扩散渗析 / 三步沉淀 / 酸回收 / 重金属回收

Key words

Stainless steel pickling wastewater / Diffusion dialysis / Three-step precipitation / Recovery of acid / Recovery of heavy metal

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基金资助

浙江省自然科学基金-联合基金-联合重点项目(LHZ22E080004)

浙江省“尖兵领雁+X”科技计划项目(2025C02241)