Scientific Development Research

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.

Coal fly ash; Nutrients; Heavy metals; Pollution risk