Development of metal oxide/metal carboxylate chemistry for the synthesis of metal tungstates, molybdates, and ferrites and extraction of iron from ores

Abstract

The research reported in this dissertation explored the application of the reactions between metal oxides and metal carboxylates for the synthesis of useful ternary metal oxides containing either molybdenum or tungsten, a green extraction process for iron ores, and the production of single-source precursors for ferrites. The reaction of lanthanum acetate with molybdenum trioxide and tungstic acid and tungsten trioxide (i.e. the MOx/acetate process) was found to produce lanthanum acetate molybdate Ln(O2CCH3)(MoO4)•1.05H2O lanthanum acetate tungstate Ln(O2CCH3)(WO4)•0.95H2O, respectively. These compounds served as single-source precursors for β-Ln2Mo2O9 and α-Ln2W2O9 at relatively low temperatures. Notably, it was possible to isolate the ionic-conductor, β-Ln2Mo2O9, as a metastable phase at room temperature. Reaction of WO3 with aqueous lanthanum acetate was incomplete and produced a green solid due to reduction of W(VI) indicating that the MOx/acetate process works best for layered compounds where intercalation of the reactants is possible. Thus, by the use of layered tungstic acid, H2WO4, the MOx/acetate process was expanded to the preparation metal tungstates, a broad class of useful materials. One limitation of the MOx/acetate process has been the hydrolytic instability of several metal acetates such as aluminum and ferric acetates. Therefore, the reaction of iron(III) nitrate with MoO3 in acetate buffer was explored that unexpectedly led to the first isolation of a trimetallic oxide via the MOx/acetate process. The reaction of iron nitrate with two molar equivalents of molybdenum trioxide produced a crystalline compound with the formula NaFe2(MoO4)2•2H2O that converted into the NaFe2Mo2O9 (a promising battery anode material) upon dehydration at 670˚C. Changing the ratio of iron nitrate to molybdenum trioxide led to isolation of amorphous solids possibly related to ferrimolybdite and ferrihydrite that upon calcining produced Fe2(MoO4)3/Fe2O3 composites that are useful partial oxidation catalysts. Lastly, a green process of extraction of iron from both pure iron oxide (Fe2O3) and iron ore were investigated using ethylenediaminetetraacetic acid (H4EDTA). Unlike other extraction processes for iron, the acid can readily be recovered and reused leading to marked reduction in waste. Besides silica dross, the by-product of the process is potassium sulfate that can be used in fertilizer manufacture. Recovery of ethylenediaminetetraacetic acid was 94% while iron was isolated as pure iron oxide with greater than 98% efficiency. The extraction reaction produces Fe(HEDTA) that catalyzes the extraction of iron due to its high acidity. Furthermore, neutralization of Fe(HEDTA) can be used to produced chelated iron that is used in fertilizers to make lawns greener and to prevent chlorosis in plants. Also, two equivalents of Fe(HEDTA react with nickel(II) hydroxide to produce a stoichiometric precursor for nickel ferrite, NiFe2O4. This opens the path to the synthesis of a large range of commercially-important ferrites.