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 synthesiz ed as precipitates from chloride + nitrate solutions of pH 1.5 with Mn2+, Z n2+, and Fe2+, or Fe3+ at temperatures between 40 and 80 degreesC using ele ctrodes 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 a nd 140 cm(2) area, respectively. Fe2+ is continuously supplied to the solut ion from oxidation of the sacrificial Fe anode, although this ion can be tr ansformed into Fe3+ by reaction with Mn3+, previously formed by anodic oxid ation of Mn2+. An energy cost of ca. 5 kWh kg(-1) is found for the batch ta nk 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 f rom the anode, are obtained. These materials have an inverse cubic spinel s tructure, being composed of nanoparticles formed by solid solutions of iwak iite, franklinite, magnetite, and maghemite. Magnetically, they behave as s oft ferrites but show lower initial permeability. In contrast, superparamag netic 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 fo rmed by amorphous mixed oxide, along with two different crystalline phases composed of hetaerolite and a mixture of iwakiite and franklinite, respecti vely.