Electrochemical route for the synthesis of new nanostructured magnetic mixed oxides of Mn, Zn, and Fe from an acidic chloride and nitrate medium

New nanostructured magnetic Mn-Zn-Fe oxides are electrochemically synthesized as precipitates from chloride + nitrate solutions of pH 1.5 with Mn2+, Zn2+, and Fe2+, or Fe3+ at temperatures between 40 and 80 degreesC using electrodes of commercial iron. The process has been studied using an undivided cell of 100 mt and a stirring batch tank of 700 mt with electrodes of 20 and 140 cm(2) area, respectively. Fe2+ is continuously supplied to the solution from oxidation of the sacrificial Fe anode, although this ion can be transformed into Fe3+ by reaction with Mn3+, previously formed by anodic oxidation of Mn2+. An energy cost of ca. 5 kWh kg(-1) is found for the batch tank at 35 mA cm(-2). For solutions up to 30 mM Mn2+ and 15 mM Zn2+, magnetic precipitates richer in Fe than in Zn and Mn, with Cu impurity proceeding from the anode, are obtained. These materials have an inverse cubic spinel structure, being composed of nanoparticles formed by solid solutions of iwakiite, franklinite, magnetite, and maghemite. Magnetically, they behave as soft ferrites but show lower initial permeability. In contrast, superparamagnetic nanoparticles are synthesized by electrolyzing solutions with 110-120 mM Mn2+ and 30 mM Zn2+. These materials with more Mn than Zn and Fe are formed by amorphous mixed oxide, along with two different crystalline phases composed of hetaerolite and a mixture of iwakiite and franklinite, respectively.