灌注重金属稳定剂对复合重金属污染河道底泥的修复效能与机理研究

Effect and mechanism of injection of heavy metal stabilizers for remediation of multiple heavy metals comminated river sediment

为探索原位灌注重金属稳定剂修复重金属污染河道底泥的可行性,以电子拆解区重金属污染物河道底泥为对象,考察了灌注Na_(2)S、CaSx和FeSO_(4)对底泥中Cr、Cd、Pb、As和Sb五种高毒性重金属的稳定化效果。结果表明:对于Cd、Pb, 3种药剂在投加30%时能完全抑制底泥中二者的浸出,而对于Cr、As和Sb, FeSO_(4)的稳定化效果最好,其次为CaSx,Na_(2)S效果最差。在FeSO_(4)投加量为3%、5%、8%和10%(质量比)时,底泥中总Cr、Cr^(6+)、As和Sb的浸出质量浓度分别降低了90%、97%、100%和100%。3种药剂处理后第7 d底泥总Cr和Cr6+浸出均出现反弹,而对于As、Sb,仅Na_(2)S和CaSx出现反弹。还原剂稳定底泥重金属的机理主要通过促进重金属由弱酸可溶态向可氧化态和残渣态转变。在3%FeSO_(4)处理基础上进一步投加5%Ca(OH)_(2),7 d后底泥Cr(VI)浸出质量浓度低于地表水Ⅲ类标准值,14 d后浓度进一步降低,效果持久。Ca(OH)2强化FeSO_(4)稳定底泥Cr的机理主要是通过促进Cr由弱酸可溶态向残渣态转变。

To explore the feasibility of in-situ pouring heavy metal stabilizers to remediate heavy metal-polluted river sediment,a comparative study of injection of Na_(2)S,CaS_(x),and FeSO_(4) on stabilization of Cr,Cd,Pb,As and Sb in the sediment from electronic waste polluted river was conducted.The three kinds of heavy metals stabilizers were added to the sediment individually with increasing concentrations from 3%to 10%.The results show that the leaching of Cd and Pb is completely inhibited by the addition of each of the three kinds of stabilizers at a dosage ratio of 30%.For stabilization of Cr、As and Sb,FeSO_(4) exhibits the best performance followed by CaS_(x) and Na_(2)S.The leaching concentrations of Cr,Cr^(6+),As and Sb are reduced by 90%,97%,100% and 100% by the addition of 3%,5%,8%,and 10%of FeSO_4,respectively.Therefore,the addition of 3%of FeSO_(4) is recommended based on the consideration of the stabilization effect of heavy metals,economic cost,and sediment compatibilization.The rebound of leaching concentrations of Cr and Cr^(6+)was found for all the three kinds of stabilizers,but the rebound of leaching concentrations of As and Sb was only found for Na_(2)S and CaS_(x).The mechanism of reducing agent stabilizing heavy metals in sediment is mainly by promoting the transformation of heavy metals from a weak acid soluble state to an oxidizable state and residue state.The leaching concentration of Cr^(6+)is reduced by lower than the threshold values for the third-grade water quality of China environmental quality standards for surface water after the sediment is treated by combined use of 5% Ca(OH)_(2) and 3%FeSO_(4) and reaction for 7 days.The leaching concentration of Cr^(6+)is found to be further decreased after reaction for 14 days,indicating a long-term persistence for Cr^(6+)stabilization.The mechanism of Ca(OH)_(2) for strengthening FeSO_(4) to stabilize Cr in sediment is mainly by promoting the transformation of Cr from a weak acid soluble state to a residual state.