Chemische und verfahrenstechnische Untersuchungen zur Erzeugung ferrithaltiger Suspensionen im Hinblick auf einen Einsatz als Zusatzstoff fuer Magnetseparation

The purpose of this research is to develop a process for the continuous removal of heavy metals from waste water using magnetic separators. Investigations concerning the formation of magnetite (Fe_3O_4) and heavy-metal ferrites (MFe_2O_4) were carried out. By the addition of these mostly ferri- or ferromagnetic substances, the magnetic properties of mixed precipitation products can be improved such that satisfactory separation efficiencies can be achieved even at moderate flux densities. When selecting the reaction temperature, ion concentrations and oxidation conditions, particular attention was paid to them being practicable in waste water treatment. The reaction variants which were applied included (1) the oxidation of an iron(II)-hydroxide suspension with air ('oxidation method') and (2) the hydroxide precipitation of iron(II) and iron(III) salt solutions ('mixing method'). The solids generated were characterised using various solid-state analytical methods and investigated with regard to their magnetic properties. Depending on the reaction conditions chosen, the precipitates were varying mixtures of the following solids: magnetite, maghemite, geothite, #delta#-FeOOH and amorphous iron(III)-oxide hydrates mostly containing sulphate. With up to about 1 mg L"-"1 min"-"1 oxygen being supplied to the reactor ('oxidation method'), magnetite was seen to be formed sufficiently at temperatures equal to and above 15 C. Using the 'mixing method' this was already achieved at a temperature of 5 C. Increasing concentrations of heavy-metal ions (e.g. Cu"2"+, Cd"2"+, Zn"2"+) or certain anions (e.g. of phosphoric or carbonic acid) lead to a reduction in the ferrite proportion of the reaction products. The saturation magnetisations of the precipitates achieved under suitable reaction conditions (60-80 A m"2 kg"-"1) are totally sufficient for the panned use. The results were confirmed in a technical-scale facility with a continuously operating packed bubble column for the generation of the magnetite suspension and a magnetic separator operated continuously in accordance with the magnetic barrier principle. This facility, operating at a filtration velocit of 3 m h"-"1, achieved 96% copper removal from waste water which had a feed concentration of c(Cu"2"+(=100 mg L"-"1)). (orig.)Available from TIB Hannover: ZA 5141(6174) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman