低浓度含砷污酸处理工艺的比较研究

比较研究了石灰中和法和石灰-铁盐法对硫化后含低浓度砷(20～50 mg/L)污酸的处理效果。结果表明,单纯采用石灰法,废水难以达标排放;而两段石灰-铁盐(氯化铁)法满足达标排放的同时,一段及二段沉淀物的浸出液中砷、镉、铜、铅和锌含量均低于危险废物鉴别标准要求(GB 5085.3-2007);其最优工艺参数为一段终了pH=2,反应时间为2 h,二段终了pH=8、Fe/As=8、反应时间为60 min、氧化剂投加量(Ca(ClO)2/As)为6∶1;正交实验结果中各参数对铁盐除砷效果影响顺序为终了pH>反应时间>Fe/As>氧化剂投加量。

A comparative study on treatment of impure acid with low-concentration arsenic

The arsenic removal efficiency from low concentration acid wastewater was evaluated by lime neutralization and the combination of lime with ferric iron in the present study. It was found that the level of arsenic, copper, lead and zinc could satisfy the limits specified by the hazardous waste discharge standard (GB 5085.3-2007) leached out of the arsenic-containing solid waste from the combination of lime with ferric iron treatment process. Therefore, the combined utilization was the preferred process because of its higher efficiency and innocuous compared with single lime neutralization. The corresponding parameters were also evaluated to achieve the optimized arsenic removal efficiency. The results indicated that the acid solutions were neutralized with lime in two hours to a final pH value of 2 in the first stage; the second-stage involved with Ca(ClO)₂ oxidation with a Ca(ClO)₂/As molar ratio of 6, ferric flocculation with a Fe/As molar ratio of 8, and lime neutralization to a final pH of 8 within an hour. After the two stages, the residual concentration of arsenic could below the tolerance level (0.3 mg/L) without any hazardous precipitates. The orthogonal design showed that the significance of the contribution of the above four factors to arsenic removal is ranked as: final pH of reacted solution > reaction time > Fe/As mole ratio > content of oxidant.