含砷、铬废水处理条件对沉渣稳定性的影响

Impact of the sewage with arsenic and chromium content on the sediment stability of the treating conditions

通过TCLP毒性程序浸出试验,以砷、铬浸出质量浓度为控制指标,对含砷、铬废水处理产生的沉渣稳定性进行了研究,并结合废水中砷、铬去除率,确定该废水的最佳处理条件。在常温下,通过调节pH值、Fe^(2+)/Cr^(6+)物质的量比、Ca/As物质的量比、曝气时间等条件对处理工艺进行优化,考察不同处理条件对废水砷、铬去除率及沉渣砷、铬浸出质量浓度的影响。结果表明,pH值为6、Fe^(2+)/Cr^(6+)物质的量比为8、Ca/As物质的量比为5、曝气时间为50 min时,不仅Cr(Ⅵ)、总铬、总砷的排放质量浓度达到了GB 8978—1996《污水综合排放标准》的要求,总砷、总铬的浸出质量浓度也分别降低到0.78 mg/L、0.59 mg/L,远低于GB/T 5085.3—2007《危险废物鉴别标准:浸出毒性鉴别》规定的质量浓度,达到了安全堆放要求。对曝气产生的絮体进行XRD测试,结果表明,余留的Fe^(2+)经曝气氧化后产生的絮体是一种无定型态的氢氧化铁或水合氧化铁,其富含阳离子空位和OH-基团,能增加砷、铬的去除率。对优化前后的沉渣进行SEM扫描,结果表明,对各因素进行优化能增大沉渣的粒径,提高沉渣的稳定性。

The paper is intended to study the impact of the sewage with arsenic and chromium content on the sediment stability of the treating conditions. For the said study purpose, we have made the toxic characteristic leachate procedure （TCLP） test over the sediment process by taking the leaching concentration of the arsenic and chromium as the control index, in combination with an investigation of the removal rate of the said two metals in hoping to determine the optimum conditions for the sewage treatment. In proceeding with our investigation, we have adjusted the different treatment conditions by regulating the room temperature and the relative parameters, such as the pH value, the Fe2＋/Cr6＋ molar ratio, the Ca/As molar ratio, and aeration time so as to optimize the treating process and find the likely effects of the different treating conditions on the removal rate of arsenic and chromium in the sewage and those on the leaching concentration of the above mentioned metals in the sediment. The results of the above investigation and exploration show that, on the condition when the pH value is 6 and the mole ratio of Fe2＋/Cr6 ＋ ： 8, whereas the mole ratio of Ca/As = 5 with the aeration time being of 50 minutes, not only the emission concentration of Cr （ VI ）, but also that of As （V）, can meet the requirements of the Integrated Sewage Discharge Standard （GB 8978-1996）. In addition, the leaching concentration of the total amount of arsenic and chromium can respectively be reduced to 0. 78 mg/L and 0. 59 mg/L, which should be considered far below the prescribed concentration of the identification standard for the hazardous wastes, i.e. the Identification for Extraction Toxicity （GB/T 5085. 3-2007 ）, and, therefore, can meet the safety stacking demands. Furthermore, the results of our experiments prove that the flock generated from the oxidation of the remaining Fe2＋ is by nature a kind of amorphous form of the iron hydroxide or hydrated ferric oxide, which is rich in cationic vacancy and hydroxyl and can help to enhance the removing rate of the two metals content. Finally, the SEM analysis of the sediment gained from the treatment before and after being optimized indicate that it is of great potentiality to increase the size of the sediment and improve its stability through optimizing the various influential factors.