This study presents a solution to solid waste problems, focusing on spent lithium-ion batteries (LiBs) and iron ore tailings (IOT) from the Mariana environmental accident in Brazil. The approach involves the production CoFe2O4 from LiBs and IOT, which serves as a catalyst for solar photo-Fenton reactions for methylene blue (MB) decolorization and as an electrochemical sensor for ascorbic acid (AA) detection. Chemical analysis showed recycling potential, with 45.22 ± 0.22% m m−1 Co from LiBs and 14.9 ± 1.5% m m−1 Fe from IOT, determined by inductively coupled plasma atomic emission spectroscopy (ICP OES) and flame atomic absorption spectrometry (FAAS). The sol-gel synthesized CoFe2O4 exhibited a crystallite size of 51.9 ± 1.3 nm and agglomerated crystal clusters. Recycled-CoFe2O4 exhibited a 98.1% MB decolorization efficiency in 60 min under solar irradiation and remained above 92.3% in all 7 reuse cycles. The electrochemical sensor exhibited a coefficient of determination of 0.9987, a sensitivity of 3.352 ± 0.0428 μA mol L−1, and a limit of detection of 0.5511 µM in the concentration range of 1.96 to 23.08 mmol L−1 for AA detection. This study demonstrates the potential of recycled-CoFe2O4 in an environmentally friendly dye removal and as an electrochemical sensor, offering sustainable waste management and resource utilization with solar energy. problems lithiumion lithium ion (LiBs IOT (IOT Brazil CoFeO CoFe O CoFe2O photoFenton photo Fenton (MB (AA 4522 45 22 45.2 022 0 0.22 m1 1 m− 149 14 9 14. 15 5 1.5 ICP OES FAAS. FAAS . (FAAS) solgel sol gel 519 51 51. 13 3 1. clusters RecycledCoFe2O4 RecycledCoFeO Recycled Recycled-CoFe2O 981 98 98.1 6 923 92 92.3 cycles 09987 9987 0.9987 3352 352 3.35 00428 0428 0.042 L1 L 05511 5511 0.551 196 96 1.9 2308 23 08 23.0 L− recycledCoFe2O4 recycledCoFeO recycled recycled-CoFe2O energy 452 4 2 45. 02 0.2 (FAAS RecycledCoFe RecycledCoFe2O 98. 92. 0998 998 0.998 335 35 3.3 0042 042 0.04 0551 551 0.55 19 230 23. recycledCoFe recycledCoFe2O 0. 099 99 0.99 33 3. 004 04 0.0 055 55 0.5 09 0.9 00 05

The correlation between iron distribution in octahedral or tetrahedral sites in synthetic magnetite and zinc spinel ferrites and their catalytic properties were investigated in this work. The zinc-doped nanomagnetites were prepared by co-precipitation method and annealed at 420 °C. X-ray diffraction, UV-Vis, X-ray absorption and 57Fe Mössbauer spectroscopies were used to identify iron sites. The obtained results showed that ZnII replaces the relatively smaller FeIII cation in the tetrahedral sites, increasing the cubic lattice dimension, and this replacement remarkably enhances the catalytic effectiveness of the Zn-spinel ferrite towards the indigo carmine degradation compared to undoped magnetite. The indigo carmine degradation experiments were carried out using photo-Fenton method in which 50 mL of indigo carmine dye aqueous solutions (20 mg L−1, pH 3.0), 20 mg ZnxFe(3-x)O4, and 2.0 mL H2O2 (aqueous solution at 0.028 mol L−1) were placed under UV light at 25 °C. Under these experimental conditions the degradation rate of indigo carmine was superior to 98%.

Frações magnéticas de duas amostras coletadas a 5 m e 52 m de profundidade, a partir do topo de um manto de intemperismo desenvolvido sobre periodito, da área de mineração de níquel em Cerro Matoso (7° 54' 31" N 75° 33' 23" O), Departamento de Córdoba, Colômbia, contêm minerais magnéticos e não magnéticos, intimamente associados. Frações magnéticas, posteriormente concentradas por tratamentos químicos seletivos com NaOH 5 mol L-1, para remover silicatos, e com uma mistura citrato - bicarbonato - ditionito (CBD), para remover óxidos de ferro não magnéticos, foram analisadas por difratometria de raios X, espectroscopia Mössbauer à temperatura do ambiente, magnetização de saturação, microscopias ótica e eletrônica por varredura e espectroscopia de energia dispersa, para se obter uma descrição detalhada das fases magnéticas presentes. Os tratamentos químicos foram efetivos na concentração dos óxidos de ferro, de tal sorte a permitir melhores resultados da análise mineralógica do minério de níquel. Os resultados Mössbauer revelaram que o tratamento com NaOH removeu silicatos e cromita e que a mistura CBD solubilizou seletivamente hematita, goethita e magnetita não estequiométrica, parcialmente oxidada.

Two magnetic samples, collected at 5 m and 52 m from the top of a weathering mantle developing on peridotite, from the Cerro Matoso (7° 54' 31" N 75° 33' 23" W) mining area for nickel, Department of Cordoba, Colombia, were submitted to magnetic separation with a hand magnet in the laboratory. The so concentrated samples were found to contain intimately associated magnetic and non-magnetic minerals. The magnetic phases were further concentrated by selective chemical treatments with 5 mol L-1 NaOH to remove silicates, and with a mixture citrate - bicarbonate - dithionite, to remove non-magnetic iron oxides. Powder X-ray diffractometry, RT Mössbauer spectroscopy, saturation magnetization measurements, scanning electron microscopy, energy dispersive spectroscopy and optical microscopy analyses were used to give a mineralogical description of the magnetic phases. The chemical treatments were effective on concentrating iron oxides so to improve the mineralogical analysis of this nickel ore. Mössbauer analysis revealed that NaOH selectively removed silicates and chromite from samples, whereas CBD dissolved hematite, goethite, and partially oxidized non-stoichiometric magnetite.