| Abstract: | Conditions of the Formation of Zinc-bearing Ferrites in Regard of Heavy Metal Removal from Wastewater by Magnetic Separation Magnetic separation techniques can be applied for heavy metal removal from wastewater if it is reached to link together the heavy metals with a substance which is sufficiently influenced by a magnetic field. Such a substance is the ferrimagnetic magnetite which can be prepared under special conditions – by oxidation of ferrous hydroxide – in wastewater. In this paper, zinc was chosen as an example for technically relevant, diamagnetic heavy metals. The investigations deal with the influence of zinc onto the structure and the magnetic properties of the reaction products produced by oxidation of zink-bearing ferrous hydroxide in aqueous solutions at room temperature. The oxidation was caused by synthetic air passing through the suspension. During the reaction, the parameters pH value, redox potential, and concentration of dissolved oxygen were observed continuously. The plots of these parameters versus time yield typical courses which can be used as measurement for the progress of the reaction. The results show that magnet ite can only be prepared if the molar ferrous concentration at the beginning is four times higher than the concentration of the dissolved oxygen. Furthermore, the oxidation rate must be slow, a condition which could be achieved by mass transfer controlled kinetics. The products of the oxidation of zinc-bearing ferrous hydroxide show a colour between black and brown. They consist of magnetite, zinc-bearing ferrite and amorphous iron hydroxide. It can be observed that with increasing initial zinc concentrations, increasing amounts of zinc-bearing ferrite but also of amorphous iron hydroxide are produced. Therefore, it seems that the impact of zinc on the reaction is in such a way that more amorphous compounds instead of the thermodynamically stabile ferrite are formed; The magnetic properties show also a dependence on the initial zinc concentration: The saturation magnetization decreases with an increase of the zinc concentration. The reaction product which results from the experiment with an initial mole ratio of Zn:Fe = 1:1 points out only paramagnetic behaviour. |
