Ferrihydrites with a Range of Crystallinities

A set of ferrihydrites with a range of crystallinities and between 2- and 6+-X-ray diffraction peaks can be produced at RT either by varying the rate of hydrolysis of a Fe(NO)3 solution or by oxidizing a FeCl2 solution containing different levels of soluble silicate. 

The reaction vessel shown in Fig. 6-1 can be used to control pH, reagent addition and gas flow. The titration is carried out at RT and with vigorous stirring. 

Place 50 mL of a 0.1 M Fe(NO)3 solution (5 mmol Fe) into the reaction vessel and automatically titrate it at a fixed rate of Iml/min with 15 mmol NaOH to a final pH of 7. To vary the rate of hydrolysis, the 

NaOH concentration is varied between 7.7 10 and 1 M in 8 steps hence the time for total neutralization is between 0.25 and 130 h and the corresponding rate of OH addition (hydrolysis rate) between 0.38 and 

200 i mol OH/mmol Fe/min. After complete hydrolysis (OH/Fe = 3), the solids are obtained by centrifugation, washed with 70mL of distilled water, dried at 40 °C and gently ground. 

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