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    磁选联合加压酸浸法脱除粉煤灰中重金属元素

    Removal of heavy metal elements in coal fly ash by magnetic separation-pressurized acid leaching

    • 摘要: 粉煤灰是大宗工业固废,其露天堆存不仅占用土地,还会造成粉尘污染等问题。粉煤灰含有微量重金属元素,可通过雨水淋浸进入到土壤和水体,造成重金属污染。因此,重金属元素脱除是粉煤灰循环再利用的关键环节。为脱除粉煤灰中重金属,以山西某煤电公司粉煤灰为原料,采用磁选法联合加压酸浸法对粉煤灰中的重金属进行脱除。分析了粉煤灰及处理产物的重金属含量,并评估了粉煤灰处理前后的潜在生态风险指数,结果表明:磁选可以初步实现对粉煤灰中的重金属元素的脱除。对磁选后的非磁性组分采用加压酸浸,深度脱除其中的重金属元素。通过正交试验和单因素试验发现,当加压酸浸的酸浓度为2.5 mol/L、液固比为10∶1、酸浸温度为160 ℃和酸浸时间为3 h时,粉煤灰中重金属实现了有效脱除,其中Cd、Cr和Pb元素的脱除率分别为79.9%、61.7%和57.6%;而As、Se和Hg元素脱除率则达到96.6%、99.2%和93.3%。磁选−加压酸浸后,粉煤灰中的Cd、Cr、Pb、As、Se残渣态的质量分数升至92%、95%、97%、88%和59%。磁选法联合加压酸浸法可以有效脱除所选粉煤灰中大部分可迁移态重金属,显著提高粉煤灰中残渣态重金属的占比,从而降低粉煤灰中重金属元素的环境迁移性和提高样品的环境安全性。为粉煤灰中重金属的脱除提供了新思路,为粉煤灰污染治理和资源化利用提供了理论基础。

       

      Abstract: Coal fly ash (CFA) is a bulk industrial solid waste. Its open-air stockpiling not only occupies land but also causes problems such as dust pollution. CFA contains trace amounts of heavy metal elements, which can leach into soil and water bodies through rainfall, causing heavy metal pollution. Therefore, the removal of heavy metal elements is a crucial step for the resource recovery and recycling of CFA. To remove heavy metals from CFA, this study utilized fly ash from a coal-fired power plant in Shanxi Province as the raw material and employed a combined method of magnetic separation and pressurized acid leaching for heavy metal removal. The heavy metal content in the raw CFA and the treated products was analyzed, and the potential ecological risk index before and after treatment was assessed. The results showed that magnetic separation could preliminarily remove some heavy metal elements from the CFA. Further applying pressurized acid leaching to the non-magnetic fraction after magnetic separation could deeply remove the heavy metals within it. Through orthogonal experiments and single-factor experiments, it was determined that under pressurized acid leaching conditions of an acid concentration of 2.5 mol/L, a liquid-to-solid ratio of 10∶1, a leaching temperature of 160 ℃, and a leaching time of 3 h, the removal of heavy metals was significantly effective: the removal rates of Cd, Cr, and Pb were 79.9%, 61.7%, and 57.6%, respectively; while the removal rates of As, Se, and Hg reached 96.6%, 99.2%, and 93.3%, respectively. After the combined magnetic separation-pressurized acid leaching treatment, the proportion of residual fractions for Cd, Cr, Pb, As, and Se in the fly ash increased to 92%, 95%, 97%, 88%, and 59%, respectively. This combined process effectively removed most of the mobile fractions of heavy metals from the target CFA, significantly increased the proportion of residual heavy metals, thereby reducing the environmental mobility of heavy metals and enhancing the environmental safety of the sample. This study provides a new approach for heavy metal removal from fly ash and lays a theoretical foundation for CFA pollution control and resource utilization.

       

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