飞灰基胶凝固砷体长期稳定性风险评价

为明确酸雨条件下飞灰基胶凝固砷体的长期稳定性，模拟2种酸度的酸雨对3种粒径状态下的固砷体进行动态淋溶实验，并运用改进多级连续提取法(Sequential Extraction Procedure, SEP)和潜在风险评估指数对固砷体进行长期稳定性风险评价。结果表明，随着浸出时间的增加，固砷体中的Al³⁺溶出并与溶液中的OH⁻反应生成Al(OH)₃胶体，且废渣中的硫化矿物氧化生成H₂SO₄、Fe₂(SO₄)₃等氧化剂，进一步加剧硫化物的氧化溶解，使得浸出液pH呈下降趋势；而且，由于飞灰固砷体粒径大小不同，表面积大小和吸附位点变化，使砷浸出过程呈现出初始、快速释放和慢速释放3个阶段的浸出特征，最高浸出质量浓度为2.42 mg·L⁻¹，累计释放量达133.78 mg·kg⁻¹，累计释放率为2.32%。SEP实验发现，原渣中的还原态砷大幅度降低，酸可提取态砷和残渣态砷增加，有利于降低固砷体的风险。潜在生态风险评价表明，在Ⅰ类和Ⅱ类建设用地筛选值为背景时，潜在生态危害程度由中等危害转为轻微危害。本研究结果可为飞灰固砷体在不同侵蚀作用下的安全处置提供参考。

Risk assessment of long-term stability of fly ash-based cementitious material containing arsenic

This paper presents a dynamic leaching test of arsenic fixation in three particle sizes based on an innovative simulation of two acid rainfall conditions in southwest China to investigate the long-term stability of fly ash-based cementitious materials that contain arsenic under acid rain conditions. Furthermore, the long-term stability risk of arsenic fixation is evaluated using a Sequential Extraction Procedure (SEP) and the potential risk assessment index. Results showed that the Al3+ in the solid arsenic bodies dissolved and reacted with the OH− in solution to form Al(OH)3 colloids as the leaching time increased. Moreover, the oxidation of sulfide minerals in the slag produced oxidants, such as H2SO4 and Fe2(SO4)3, which further aggravated the oxidative dissolution of sulfides, thereby resulting in an overall decreasing pH value of the leachate. In addition, due to the varying particle sizes of the fly ash solid arsenic bodies, surface area size, and adsorption site changes, the arsenic leaching process showed three stages of leaching characteristics, namely, initial, rapid, and slow release, with a maximum leaching concentration of 2.42 mg·L−1, the cumulative release of 133.78 mg·kg−1, and the cumulative release rate of 2.32%. The SEP test revealed that the reduced state of arsenic in the raw slag was lowered substantially, and the acid extractable state and residual state of arsenic were increased, which was conducive to lessening the risk of arsenic fixation bodies. The evaluation of the potential ecological risk showed that the potential ecological hazard when the screening value of Class Ⅰ and Class Ⅱ construction sites was the background changed from moderate hazard to slight hazard.