环境地球化学国家重点实验室知识库

The aqueous Fe²⁺ (Fe²⁺_aq)–induced recrystallization of iron minerals is an important geochemical process with critical effects on the environmental behavior of metal pollutants in soils. However, the effects of different heavy metals with distinctive physicochemical properties on the Fe²⁺_aq–induced recrystallization of iron minerals and the different stabilization behaviors of these heavy metals remain unclear. This study examined the effects of Cd²⁺ and Cr³⁺ on the Fe²⁺_aq–induced recrystallization of Al‐substituted goethites and the simultaneous stabilization of Cd²⁺/Cr³⁺ ions by the recrystallized Al‐substituted goethites. Results from stable Fe isotopic tracer experiments and Mössbauer characterization show that Fe atoms were exchanged between Fe²⁺_aq and structural Fe(III) in Al‐substituted goethites with coexisting Cd²⁺/Cr³⁺, although both Cd²⁺ and Cr³⁺ decreased the exchange rates. During the Fe atom exchange, Al‐substituted goethites were recrystallized and a portion of Cd²⁺/Cr³⁺ ions were stabilized by the resulting goethite products. Compared with Cd²⁺, more Cr³⁺ ions were immobilized by the recrystallized Al‐substituted goethites due to the lower hydrolysis constant of Cr³⁺ than Cd²⁺, as well as the closer ionic radius of Cr³⁺ with Fe³⁺ and Al³⁺. Al‐goethites with higher Al contents further decreased the Fe atom exchange rates while increasing the amounts of immobilized metal ions when in the presence of Cd²⁺ or Cr³⁺. The findings of the present study suggest that the physicochemical properties of metal ions play critical roles in affecting their environmental behavior and fates during Fe²⁺_aq–induced recrystallization of iron minerals in soils.