Study On The Catalytic Phase Transformation Mechanism Of Ferric Hydroxide/oxohydroxides

Iron oxides are of importance in our environment and biological functions, which almost exist in all of the global system. The diversity and the different structure and thermodynamic stability of iron oxides give rise to the complicated interconversions between different forms. Thus, much attention has been paid to the transformations between different forms, as well as the reductive dissolution of iron oxides/hydroxides in the presence of Fe(II) ion or other reductant. Our earlier experimental results show that trace Fe(II) has obvious catalytic role in the transformation of ferric hydroxide. The main aim of this work is to investigate the transformation of ferric hydroxide and oxohydroxides plus Fe(II) in neutral pH ranges. The main research aspects are summaried as follows:(1)The phase transformation of Fe(OH)3 gel prepared by ferric sulphate was investigated by changes of the initial pH, the transformation temperature, the ferric hydroxide formation condition and heating rate. The results indicated that there were α-FeOOH and α-Fe₂O₃ detected during the catalytic phase transformation of ferric hydroxide under our disquisitive condition. The product species varied with the transformation temperature. At t≤40℃,the transformation product only contained α-FeOOH. At 40℃2O₃. Pure α-Fe₂O₃ could be obtained at t≥80℃. As well as the initial pH, the ferric hydroxide formation conditions and heating rate also affected the phase transformation product species of Fe(OH)₃ gel. The above results were reasonably explained by the accelerating effect of Fe(II) on Fe(OH)₃ gel's dissolution and solid state transformation.(2)The phase transformation of Fe(OH)₃ gel prepared by ferric nitrate was investigated by changes of the initial pH, the transformation temperature, the ferric hydroxide formation condition and heating rate. The results indicated that γ-FeOOH was detected in the product besides α-FeOOH and α-Fe₂O₃, which reflect the effect of anion on Fe(OH)₃ gel's transformation. The product species varied with thetransformation temperature. At t ^ 40 °C , the product contained y-FeOOH and a-FeOOH. At 40°C 3. Moreover, the transformation mechanism of a-FeOOH related to the size of a-FeOOH.