伴矿景天汁液中重金属形态及絮凝沉淀效果优化

超积累植物伴矿景天在镉污染土壤修复方面展现出广泛的应用前景,而收获后鲜样的快速脱水处置是目前急需解决的问题。采用连续浸提法研究了伴矿景天植株中重金属浓度及形态,正交实验探讨了汁液在絮凝沉淀过程中重金属及化学需氧量(COD)的去除效果及其影响因素,Cd离子选择电极测定了汁液处理前后镉形态变化。结果表明,伴矿景天植株中Cd、Pb主要以活性较低的盐提取态和酸提取态存在,Zn主要以活性较高的乙醇提取态和去离子水提取态存在；汁液中离子态Cd约占总浓度的20%,其余主要为非离子态；絮凝沉淀可有效去除汁液COD和重金属,优选条件pH为10,聚合氯化铝(PAC)投加量2%,搅拌速度为400 r·min-1,该条件下汁液Cd、Pb、Zn和COD去除率分别为81.9%、77.0%、76.4%和55.0%。汁液经絮凝沉淀后,Cd总浓度降低到0.23 mg·L-1,且主要为非离子态。伴矿景天汁液中重金属的形态对汁液的絮凝沉淀效果有较大影响,有机螯合态重金属难以通过絮凝沉淀彻底去除,而离子态重金属在絮凝沉淀中更容易被去除。

Fractions of heavy metals in Sedum plumbizincicola juice and their flocculation precipitation optimization

Sedum plumbizincicola(S. plumbizincicola), a hyperaccumulator, has been potentially used in the remediation of cadmium (Cd) polluted soil. However, it is necessary for the quick dewatering and deposition of fresh biomass. The concentrations of heavy metals in S. plumbizincicola tissues were studied by sequential extraction procedures. Besides, the key parameters that affect removal rate of heavy metals and chemical oxygen demand (COD) during the process of flocculation precipitation were investigated. The change of Cd fraction in S.plumbizincicola juice was acquired by Cd ion-selective electrode. The results revealed that NaCl, HAc and HCl soluble forms were main fractions for Cd and Pb in plant tissues, while water and ethanol soluble forms which possess high chemical activity were main fractions for Zn. Furthermore, Cd2+ concentration accounted for roughly 20% of the total Cd in the juice, while the dominating forms of Cd were non-ionic. The effects of pH, dosage of polyaluminium chloride (PAC) and agitation speed on precipitation efficiency of heave metals and COD in S.plumbizincicola juice were analyzed by orthogonal experiment. The optimal conditions of precipitation were pH 10, PAC 2% and agitation speed at 400 r·min-1. At this condition, removal rate of Cd, Pb, Zn and COD were 81.9%, 77.0%, 76.4% and 55.0%, respectively. After flocculation precipitation, the total concentration of Cd in S. plumbizincicola juice declined to 0.23 mg·L-1. The forms of heavy metals in S. plumbizincicola juice greatly influenced their removal rate. Heavy metal in ion form was easier to be removed by flocculation precipitation than that in organic chelated form.