干湿交替对碱性煤矸石中重金属释放潜能影响及风险评价

Release potential and risk assessment of heavy metals from alkaline coal gangue under drying-wetting cycles

为探究干湿交替对碱性煤矸石中重金属释放潜能和赋存形态的影响,以陕西省榆林市某矿区碱性煤矸石为试验对象,通过静态浸泡和动态淋滤试验,研究了干湿交替作用对碱性煤矸石中重金属Fe、Cu、Cr释放潜能的影响规律。同时通过五步提取试验,探讨了各重金属的赋存形态变化规律,并通过风险评价准则(Risk Assessment Code,RAC)对重金属进行了潜在生态风险评价。结果表明:碱性煤矸石中重金属释放主要以动态淋滤过程为主,经干湿交替处理后的煤矸石样品,在静态浸泡条件下各重金属元素的释放潜能均小于动态淋滤过程;在动态淋滤试验中,不同含水率、不同干湿交替周期处理后的煤矸石样品其碱度和和重金属元素的释放潜能均会出现不同程度的下降,且含水率为30%条件下较60%下降更为明显。在含水率30%条件下,碱度和Fe、Cu、Cr的累积释放率最高,分别降低了0.0124%、0.0098%、5.4802%、1.4285%;Fe、Cu、Cr的赋存形态发生转化,在含水率60%条件下,干湿交替14次时,Cu的残渣相较空白组降低了18.76%;RAC潜在生态风险危险评价表明未经干湿交替处理的煤矸石Fe、Cu、Cr的风险等级分别为无污染、中度污染、轻度污染,经处理后的煤矸石中Fe、Cu、Cr活性形态质量比都有不同程度的提高,Cu的潜在风险等级由轻度风险提高到中度风险。

To research the effect of drying-wetting cycles on the release potential and speciation of heavy metals in alkaline gangue,we studied the effect of drying-wetting cycles on the release potential of heavy metals Fe,Cu,and Cr in alkaline gangue by static soaking and dynamic leaching test in a mining area in Yulin,Shaanxi Province.Besides,through Tessier's sequential extractions,the changes in the speciation of each heavy metal were explored,and the potential ecological risk of heavy metals was evaluated by the RAC risk evaluation method.The results show that:the release of heavy metals in alkaline gangue is mainly based on the dynamic leaching process.After drying-wetting cycles treatment of gangue samples,the release potential of each heavy metal element is smaller than that of the leaching process under static soaking conditions;in the dynamic leaching test,the release potential of the alkalinity and heavy metal elements of gangue samples with different drying-wetting cycles decrease in different degrees,and the water content of 30%is more obvious than the water content of 60%decline;under the condition of 30%water content,the cumulative release rate of alkalinity and Fe,Cu,and Cr are reduced by 0.0124%,0.0098%,5.4802%,and 1.4285%,respectively;the speciation of Fe,Cu,and Cr is significantly transformed,under the condition of 60%water content,the proportion of residual state of Cu decreased by 18.76%compared with the control group after drying-wetting cycles 14 times;risk assessment code shows that the potential ecological risk level of Fe,Cu,and Cr of coal gangue in the blank group are no pollution,moderate pollution,light pollution,and the proportion of Fe,Cu,and Cr active speciation in coal gangue after dryingwetting cycles have different degrees of improvement,and the potential risk level is increased,and the potential risk level of Cu is increased from light risk to moderate risk.