不同铁矿物对水稻土砷的稳定化效果及机制

水淹缺氧条件是驱动水稻土砷释放引起砷污染的主要原因,其中,铁矿物在砷的迁移转化过程中扮演重要的角色.为研究水铁矿、针铁矿和赤铁矿对水稻土砷的稳定化效果,分析了3种铁矿物对土壤溶液砷浓度的影响,采用土壤溶液中亚铁和总铁的浓度变化来评估不同铁矿物对砷的稳定化效果,并对3种铁矿物进行扫描电镜(SEM)和X射线衍射(XRD)等表征分析.结果表明,水铁矿具有最大的比表面积,为192.54m2·g-1,且微孔孔容达到0.069 cm3·g~(-1),针铁矿和赤铁矿依次减少,而3种铁矿物的结晶度以针铁矿最高,赤铁矿和水铁矿依次降低.施用水铁矿、针铁矿和赤铁矿均有效地降低了土壤溶液中砷的浓度,当添加量为2.0%(质量分数)时,土壤溶液中砷浓度分别降低62.55%、61.36%和55.16%.相关性分析表明,随着无定形铁含量的提高,其对砷的稳定化效果趋于显著,其中,土壤无定型铁与无定型结合态砷含量存在正相关关系(r=0.879,p=0.009),而与土壤溶液砷存在负相关关系(r=-0.895,p=0.006).

Stabilization effect of arsenic by different iron minerals in paddy soils and the related mechanism

An increased arsenic release generally occurs under flooded and anaerobic condition in paddy soils, thus causing high arsenic contamination in the soil. Iron minerals play important roles in arsenic transformation and transport in paddy soil, while the mechanisms involved are largely unknown. To investigate the effects of different iron minerals (ferrihydrite, goethite and hematite) on stabilization of soil arsenic, their influence on soil solution, as well as ferrous iron and total ferric iron content in soil solution were analyzed. Scanning electron microscopy(SEM) and X-ray diffraction(XRD) analysis were employed for surface characterization of the iron minerals. Results showed that ferrihydrite had the largest specific surface area (up to 192.54 m²·g^-1), with micropore volume being as high as 0.069 cm³·g^-1, followed by goethite and hematite. However, goethite is the highest one in terms of crystallinity, followed by hematite and ferrihydrite. Application of ferrihydrite, goethite and hematite at an dosage of 2.0% (m/m) decreased arsenic content in soil solution by 62.5%, 61.36% and 55.16%, respectively. Correlation analysis revealed that stabilization of soil arsenic was enhanced by the increase of amorphous iron levels in soil. Soil amorphous iron content showed a positive correlation with amorphous iron bound arsenic content(r=0.879, p=0.009), but was negatively correlated to arsenic content in soil solution(r=-0.895, p=0.006).