CaO和方解石钝化不同污染程度煤矸石性能与机理

Passivation performance and mechanism of coal gangue with different pollution levels based on CaO and calcite

煤矸石是一种典型的工业废弃物,大量的煤矸石堆积会造成各种环境问题以及资源浪费.在环境问题中,重金属污染最为严重.本文采用CaO和方解石对不同污染程度的煤矸石中重金属进行钝化,并探究其钝化机理.结果表明,CaO和方解石均有较好的钝化效果,能使中高度污染的煤矸石转化为轻度污染或无污染,CaO钝化Pb^(2+)、Zn^(2+)、Cu^(2+)的平均钝化率分别为37.4%、37.8%、25.5%;方解石钝化Pb^(2+)、Zn^(2+)、Cu^(2+)的平均钝化率分别为53.8%、43.5%、34.4%,方解石钝化效果略优于CaO.通过对钝化前后煤矸石的表征和Visual MINTEQ软件模拟,CaO可以通过提高煤矸石pH并提供OH^(−),与重金属离子结合生成难溶或不溶的氢氧化物沉淀;方解石不仅能提高体系的pH,还能提供CO_(3)^(2−),CO_(3)^(2−)与重金属离子结合生成难溶或不溶的碳酸盐.两者钝化均将煤矸石中可流动态重金属转化成残渣态重金属.对钝化前后的煤矸石进行模拟酸雨溶出实验,钝化后的煤矸石中各重金属成分较稳定,溶出风险明显低于原煤矸石,均在风险管控标准以下.综上,该方法能有效地钝化煤矸石中的重金属,为煤矸石的无害化,尤其是重金属污染的稳定化提供了有效的手段.

Coal gangue represents a substantial bulk solid waste, which is the main by-product of coal mining and processing, accounting for 10% to25% of the total mining output. Its current aggregate exceeds 6 billion tons, with an annual growth rate of 800 million tons. As aquintessential form of industrial waste, the extensive accumulation of coal gangue results in significant environmental concerns. Coalgangue harbors a multitude of pollutants with heavy metal pollution notably pronounced. Upon exposure to atmospheric, aquatic, and soilenvironments, heavy metals in coal gangue can dissolve, migrate, and transform into more hazardous forms, resulting in environmentalpollution and potential health risks to humans. Particularly for communities residing near coal mines, prolonged exposure to heavy metalsin coal gangue markedly elevates their health risks. Consequently, the detoxification of coal gangue prior to its resourceful utilizationholds paramount importance.Typically, two approaches are employed to diminish the bioavailable forms of heavy metals in coal gangue. One strategy involves theextraction of heavy metals through the application of leaching agents. Although this method is effective, this approach may lead topotential secondary pollution. Alternatively, heavy metals can be passivated. Passivation effectively reduces the bioavailable state ofheavy metals, rendering them more stable and less prone to migration. Passivation stands out as an efficacious approach for heavy metalpollution treatment, notable for its large-scale applicability, straightforward procedure, and significant remediation results. This researchutilized CaO and calcite for the passivation of coal gangue contaminated at different levels. Experimental results revealed that both CaOand calcite had decent passivation performances on heavy metals in coal gangue, effectively reducing moderate or high level pollution ofcoal gangue to a slight or clean level of pollution. The passivation effect of calcite was slightly better than that of CaO, with the averagepassivation efficiency of CaO on Pb^(2+), Zn^(2+) and Cu^(2+) of 37.4%, 37.8% and 25.5%, and the average passivation efficiency of calcite onPb^(2+), Zn^(2+) and Cu^(2+) of 53.8%, 43.5% and 34.4%, respectively.Passivation processes using CaO and calcite convert the active heavy metals in coal gangue into residual form. Characterization wasconducted on coal gangue pre- and post-passivation. SEM analysis revealed that post-passivation coal gangue had a denser structure,more surface grooves, and a significant number of small particles adhering to its surface. The passivating agents successfully adhered tothe coal gangue surface or formed precipitates post-passivation. XRD results revealed insoluble substances containing heavy metals inthe post-passivation coal gangue. The formed precipitates within the system likely interact with other groups to form various insolubleminerals, contributing to the passivation effect.Visual MINTEQ software was utilized to simulate the passivation process, modeling the behavior of heavy metal ions under varyingpH levels and temperatures. Simulation findings indicated that CaO formed insoluble hydroxide precipitates by supplying OH^(−) ions andelevating pH levels, subsequently binding with heavy metal ions. Furthermore, calcite, in addition to increasing the system’s pH, alsocontributed CO_(3)^(2−), which leaded to the formation of insoluble carbonates that binded with heavy metal ions in the coal gangue.Under the post-passivation, the coal gangue exhibited favorable results in simulated acid rain leaching experiments. In the CaO-treatedsystem, heavy metal ions were undetected post-leaching due to the rise in overall pH of the coal gangue following CaO passivation, whichneutralized the effects of simulated acid rain, thereby inhibiting heavy metal ion leaching. Post-passivation with calcite, there was amarked reduction in leaching, demonstrating that passivation effectively impedes the mobility of heavy metals. The utilization of CaOand calcite for passivation is demonstrated to be effective in immobilizing heavy metals in coal gangue, offering significant implicationsfor detoxifying coal gangue and treating industrial heavy metal pollution.