Abstract:

Tungsten is a contaminant that has received relatively little attention, and our understanding of its environmental behavior remains limited. In surficial environments, the Fe mineral-water interface plays a crucial role in regulating the solid-liquid distribution and speciation of tungsten and other oxyanions, making it significant for predicting the migration and fate of tungsten. This study investigates the speciation, transformation, and redistribution of tungsten during the crystallization of ferrihydrite with the aim of providing scientific evidence for the migration, transformation, and fate of tungsten in surface environments. Ferrihydrite-tungsten adsorption (FhW_Ads) and co-precipitation (FhW_Cor) complexes were prepared using a 2-line ferrihydrite synthesis method. Aging experiments were conducted for 60 days under aerobic conditions at 60 ℃. The transformation of ferrihydrite and speciation of tungsten were analyzed using X-ray diffraction and chemical speciation extraction. The results indicated that in the absence of tungsten, 82% of the ferrihydrite was transformed into goethite or hematite after 60 days. In the FhW_Ads and FhW_Cor systems, the characteristic diffraction peaks of goethite or hematite appeared later and were weaker in intensity. Ultimately, 73% of the ferrihydrite was transformed in the FhW_Ads system, and 57% in the FhW_Cor system, suggesting that tungsten inhibits ferrihydrite crystallization, with co-precipitation showing a more pronounced inhibitory effect. During the crystallization of ferrihydrite, tungsten was gradually released into the solution, and the amount of tungsten released in the FhW_Ads system (154 mg∙L⁻¹) was higher than that in the FhW_Cor system (110 mg∙L⁻¹). The released tungsten is subsequently re-adsorbed by the transformation products. In addition to being released into the solution, tungsten may be partially incorporated into the mineral lattice or transformed into crystalline tungsten-iron compounds during mineral phase transformation. The results of this study confirm that iron minerals serve as important “reservoirs” for tungsten, and that iron-tungsten complexation and mineral phase transformation significantly alter the binding speciation and redistribution of tungsten, further influencing its migration and fate. This study provides valuable insights into the environmental behavior of tungsten in iron-rich environments.

Key words: ferrihydrite, crystallization transformation, tungsten, adsorption, coprecipitation

摘要：

钨是一种受关注较少的污染物，目前对其环境行为的认识还十分有限。在表生环境中，铁矿物-水界面是调控钨等含氧阴离子固液分配和形态的关键界面，对预测钨的迁移和归趋有重要意义。探究水铁矿结晶转化过程中钨的形态转化和再分配，旨在为钨在表生环境中的迁移转化和归宿提供科学依据。参考2-line水铁矿的制备方法合成水铁矿-钨吸附（FhW_Ads）和共沉淀（FhW_Cor）复合体，在60 ℃好氧条件下进行为期60 d的老化试验，结合X射线衍射和化学形态提取，研究水铁矿转化及钨的形态特征。结果显示：在无钨存在，60 d后最终有82%的水铁矿转化为针铁矿或赤铁矿；而在FhW_Ads和FhW_Cor体系中，针铁矿或赤铁矿特征衍射峰出现时间较晚且强度更弱，最终FhW_Ads体系中水铁矿转化了73%，FhW_Cor体系中转化了57%，意味着钨抑制水铁矿的结晶转化，且共沉淀方式抑制效果更显著。在水铁矿结晶转化过程中，钨逐渐被释放到溶液中，且FhW_Ads体系中钨的释放量（154 mg∙L⁻¹）高于FhW_Cor体系（110 mg∙L⁻¹）；被释放的钨随后被转化产物再吸附。在矿相转化过程中，钨除了被释放到溶液中，还部分插入矿物晶格内，部分可能转化为结晶态钨铁矿（FeWO₄）。该研究结果证实，铁矿物是钨的重要“库”，且铁-钨的复合方式和矿相转化显著改变钨的结合形态和再分配，进一步影响其迁移和归趋。这对理解钨在富铁环境中的环境行为提供了支撑。

关键词: 水铁矿, 矿相转化, 钨, 吸附, 共沉淀