Investigation into the nutritional status and heavy metal forms in acid-alkali modified fly ash
酸碱改性粉煤灰的养分与重金属赋存特征研究

摘要

为实现粉煤灰固体废弃物资源化利用，降低其直接施用于土壤带来的环境风险，本研究以新疆准东电厂粉煤灰（Fa）、氢氧化钠改性粉煤灰（NFa）和柠檬酸改性粉煤灰（CFa）为研究对象，系统开展改性粉煤灰的养分与重金属赋存特征研究。采用扫描电子显微镜（SEM）表征粉煤灰改性前后的微观结构特征，测定其有机质、速效磷、速效钾、全氮、氨氮等核心养分指标；结合 Tessier 连续提取法分析粉煤灰改性前后重金属的赋存形态变化，并运用内梅罗综合污染指数评价其环境安全性。结果表明：原始粉煤灰（Fa）养分含量极低（如速效钾仅18.92 mg/kg）。酸碱改性均能显著提升其养分供给能力，其中NFa的速效钾含量增至514 mg/kg，为Fa的26.2倍；CFa的速效磷含量亦增幅显著。酸碱改性可有效降低粉煤灰中Cr、As等重金属的活性态比例，实现重金属的有效钝化；NFa和CFa的内梅罗综合污染指数分别为 0.537和0.540，均处于清洁水平。综上，酸碱改性可同步实现粉煤灰的养分提升与重金属钝化，有效降低其施用的环境风险，研究结果为粉煤灰在土壤改良领域的安全、合理资源化利用提供了重要科学依据。

Abstract

This study aimed to realize the resource utilization of coal fly ash and reduce the environmental risks of its direct application in soil. Raw fly ash (Fa) from Zhundong Power Plant in Xinjiang, NaOH-modified fly ash (NFa), and citric acid-modified fly ash (CFa) were used as research materials. The microstructure was characterized by scanning electron microscopy (SEM). Key nutrient indexes including organic matter, available phosphorus, available potassium, total nitrogen, and ammonia nitrogen were determined. The chemical fractions of heavy metals were analyzed by the Tessier sequential extraction procedure, and the environmental safety was evaluated using the Nemerow integrated pollution index. The results showed that the nutrient content of raw fly ash (Fa) was extremely low, with available potassium of only 18.92 mg/kg. Both acid and alkali modification significantly improved the nutrient supply capacity. The available potassium content of NFa reached 514 mg/kg, which was 26.2 times that of Fa, and CFa also showed a remarkable increase in available phosphorus. Meanwhile, modification effectively reduced the proportion of active fractions of Cr, As and other heavy metals, achieving efficient immobilization. The Nemerow integrated pollution indices of NFa and CFa were 0.537 and 0.540, respectively, both at a clean level. In conclusion, acid and alkali modification can synchronously improve nutrient availability and immobilize heavy metals in fly ash, thus effectively reducing environmental risks. The results provide an important scientific basis for the safe and rational resource utilization of fly ash in soil improvement.