Synthesis of Iron-Doped Manganese Oxides with an Ion-Sieve Property: Lithium Adsorption from Bolivian Brine

Iron-doped lithium manganese oxides Li1.33FexMn1.67-xO4 (x = 0.15, 0.30, and 0.40) were prepared by calcination of carbonates of Li, Mn, and nitrate of Fe in air at 350, 400, 450, 550, and 650 degrees C. The calcined samples, characterized by X-ray diffraction (XRD) and chemical analysis, were spinels. The protonated samples after treatment with HCl solution were tested as adsorbents for lithium adsorption from the salt lake brine collected from the Salar de Uyuni, Bolivia. The precursor showed 3.7% Mn extraction upon acid treatment with Fe/Mn ratio of 0.1 obtained from calcination at 450 degrees C. The amount of Mn extracted in HCl solution decreased with increasing of Fe/Mn ratio, and the amounts of lithium extraction were 90%, 96%, and 91% for Fe/Mn = 0.1, Fe/Mn = 0.2, and Fe/Mn = 0.3, respectively, while the amounts of dissolved iron showed the opposite trend. By studying the lithium adsorption in the raw brine and NaOH-added brine by a batch method, the adsorbent with Fe/Mn ratio of 0.1 obtained from calcination of the precursor at 450 degrees C was found to be efficient lithium adsorbent with lithium uptake of 18 mg/g at final pH 2.0 from the raw brine (initial pH 6.7) and 28 mg/g at final pH 7.2 from the NaOH-added brine (initial pH 8.2). The adsorbent with Fe/Mn ratio of 0.1 obtained from calcination of the precursor at 450 degrees C was evaluated for a 4 cycle adsorption/desorption experiment. The amount of manganese extracted (%) in the solution decreased with cycle numbers, 1.1% in the first cycle and 0.70% in the fourth cycle.