Influence of Nitrate and Perchlorate Anions on the Kinetics of the Goethite Formation

The synthesis of goethite by oxidation of ferrous iron solutions in the presence of metallic iron has been carried out at temperatures ranging from 20 to 70°C and initial pH form 1 to 4; air flow rate is kept constant at 1 L/min. The influence of nitrate and perchlorate anions has been studied for salt concentrations ranging from 0 to 1 mol/L. The rates of iron oxidation and goethite precipitation are significantly enhanced. As expected, the nitrate anion presents many more marked oxidative properties than perchlorate. Domains of precipitation of goethite have been determined and presented in diagrams based on the factors cited above. In the presence of nitrate, magnetite precipitates in large domains corresponding to an increase in either temperature or pH. Ferrous iron concentrations are very low during magnetite precipitation, below 2 × 10−3g/L. They remain constant during the precipitation of goethite, in the range 12–18 × 10−3g/L.