Combined Effect of Arsenic and Cadmium on the Transformation of Ferrihydrite into Crystalline Products

Ferrihydrite, prepared in the presence of different amount of As and Cd in the solution, was used to study the combined effect of As and Cd coexisted in the same system on the transformation of ferrihydrite into crystalline products at pH & and pH 12. The data showed that there was apparent interaction between As and Cd in the transformation process. At pH 8, the transformation product was hematite with 1% As and different percent Cd (mole fraction, so as the follows), but the size of particles formed with different amount of Cd was different. At pH 12, the transformation products varied from sole hematite with 1% As and less than 2% Cd to a mixture of hematite and goethite with more than and equal to 2% Cd, and the percentage of goethite in the transformation products increased with the increasing level of Cd in the system. XRD (X-ray diffraction) and chemical analysis data showed that almost all As and part of Cd initially present in the system were retained in the crystalline products. The presence of As increased the amount of Cd retained in the structure of iron oxide. SEM (Scanning Electron Microscope) examination showed that the presence of As and Cd also altered the morphology of crystalline products.