Synthetic data report the ball-milling of mined iron ore tailings (IOTs) dried at 100°C. These were milled using a laboratory ball mill (internal diameter 300 mm and length 300 mm, using 150 steel alloy balls and an ore-to-ball ratio of 0.5 with a milling time of 30 min). Conversion of the resulting ≤50 μm IOTs to aqueous (soluble) FeCl3 removed insoluble Al-, Si-, Mg- and Ca-based minerals. This was done by the described sequential heating and filtering protocol. The conversion of FeCl3 to magnetite nanoparticles (NPs) by reduction with excess dextrose is described. Conditions of pH control, heating and washing are included. Powder X-ray diffraction (PXRD) data (obtained for 20–75° 2θ using Ni-filtered Cu Kα (λ = 0.15418 nm) radiation and a data step size of 0.02° 2θ and counting time of 2 s per step) of the resulting magnetite is presented in graphical (OriginPro) and raw (Excel) formats. Scanning electron microscopy (SEM) was combined with energy dispersive X-ray spectroscopy (EDX) to evaluate morphology and size distribution of IOTs and magnetite. IOTs analysed by SEM on a Hitachi S3400N (accelerating voltage 15 kV) and magnetite analysed on a field emission (FE) TESCAN MIRA 3 SEM (accelerating voltage 30 kV) at high (scale bar 100-200 nm) and low magnification (scale bar 1-100 μm). EDX data were obtained using a Horiba EX-400 identified Fe content (at%) at the red spot indicated in the corresponding SEM image. Transmission electron microscopy (TEM) followed sample sonication in EtOH and then drop-casting onto holey carbon copper grids. Magnetite NPs only were analysed using a FEI Philips Tecnai 20 with an accelerating voltage 200 KeV and a 70 μm objective aperture. Low magnification brightfield imaging (scale bars 10-100 nm) were employed to obtain a mean size distribution based on 100 NPs. High-resolution (HR) brightfield imaging and combined High-angle annular dark-field (HAADF) scanning TEM (STEM) and EDX analysis used a Thermo Scientific Talos F200X G2 TEM fitted with a Super-X EDS detector system. EDX detected Fe content (at%) in the white square panels indicated in representative HAADF images. Selected-area electron diffraction (SAED) data for magnetite were obtained with a 40 μm aperture. X-ray photoelectron spectroscopy (XPS) is presented in processed (OriginPro) and raw (Excel) formats. XPS signals were referenced using the C1s peak at 284.6 eV. FT-Infrared spectra of magnetite NPs were measured using a JASCO FT/IR-4000 in the range 400–4000 cm–1 and raw and processed data are reported. Thermogravimetric analysis (TGA) data were obtained for magnetite coated with dextrose on a TA Instruments TGA 500. Data acquisition was in the range 25-750 °C in N2 (ramp rate 10 °C min–1). UV-vis diffuse reflectance spectroscopy (UV-vis DRS) of magnetite was collected on a Varian Cary-50 UV-vis spectrophotometer with a Harrick Video-Barrelino diffuse reflectance probe. Photoluminescence (PL) and excitation (PLE) spectra of magnetite required dispersion in ethanol (1.0 × 10–5 M concentration of magnetite). PL spectra were recorded using Perkin-Elmer LS 55 fluorescence spectrometer. Magnetization of both IOTs and magnetite NPs were Recorded on a SQUID magnetometer (Quantum DesignMPMS XL-7) at 300 K in the range +/-30 kOe. Photocatalytic activity was analysed by degrading bodactive red BNC-BS dye in aqueous H2O2 under simulated solar irradiation (100 W Xenon lamp fitted with a UV cut-off filter, Solar Simulator-Royal Enterprise, 1 sun illumination, 100 mW cm-2). For testing, 25 mg of magnetite NPs were added to 50 ml of 1.0 x 10–5 M aqueous dye. The mixture was kept in the dark for 45 mins. before a 5.0 ml aliquot was withdrawn and centrifuged. The 418 nm absorption for the dye was used to determine the dye concentration before photocatalysis. The remaining suspension was treated with H2O2 (250 µl) and then irradiated. Dye degradation was monitored in triplicated experiments over 180 mins. by UV-vis spectroscopy. The solution was kept ice-cold throughout. Reference experiments without irradiation in the presence of catalyst but without H2O2 and with light irradiation in the absence of catalyst but presence of H2O2 were also done. To show hydroxyl radical photoformation a terephthalic acid (TA) probe was used. Catalyst (25 mg) was dispersed 30 ml TA (5 × 10−4 M), NaOH (2 × 10−3 M) and 0.15 ml H2O2. During irradiation, 3.0 ml aliquots were withdrawn at 30 min. intervals, centrifuged, and the fluorescence emission of the supernatant measured (excitation at 315 nm, emission at 425 nm for hydroxylated TA).