Preparation and formation mechanism of nano-iron oxide black pigment from blast furnace flue dust

A mixed solution of ferrous and ferric sulfate leached from blast furnace (BF) flue dust was used to prepare nanometer-sized iron oxide black pigment (Fe3O4, magnetite) by the co-precipitation method. The pH value played a very important role in affecting the color and particle size of Fe3O4 and the evolution of green rust in to Fe3O4 or FeOOH. The experimental conditions including the solution pH, the way of adding precipitant, volume of air and reaction time for the formation of nano-iron oxide black pigment were investigated carefully in order to determine the optimal ones. The color, morphology and particle size of as-prepared Fe3O4 pigment were characterized by means of a color measurement instrument, X-ray diffraction (XRD) and transmission electron microscopy (TEM) respectively. The results showed that the obtained pigment had low average spectral reflectance (<4%), good oil absorption (∼23%), high black intensity and narrow size distribution of 60–70 nm. Furthermore, the formation mechanism of Fe3O4 from the mixed solution of ferrous and ferric sulfate was discussed.