Adsorption of methylene blue on magnetite humic acid: Kinetic, isotherm, thermodynamic, and regeneration studies

[Display omitted] •Preparation of Magnetite Humic Acid (MHA) 3:1, 2.5:1, 2:1, and 1.5:1 was successful.•MHA improved the adsorption of methylene blue.•MHA has easily separated the adsorbent and adsorbate using an external magnet.•The highest maximum adsorption capacity is MHA 2.5:1 (161.290 mg/g)•MHA regeneration efficiency from 92.28% to 58.92% in the fifth cycle. Preparation of Magnetite Humic Acid (MHA) 3:1, 2.5:1, 2:1, and 1.5:1 was successful as evidenced by the characterization using FTIR, XRD, VSM, SEM-EDS analysis. The FTIR spectra have a typical absorption at 3425, 1604, 1396, 1095, 1026, 910, 794, and 540 cm−1. XRD patterns show diffraction peaks at 2θ = 20.40 °, 35.63°, and 63.3°. MHA 3:1, 2.5:1, 2:1, and 1.5:1 was paramagnetic with magnetization (Ms) at 20.44, 17.04, 15.51, and 13.82 emu/g, respectively. The surface of MHA is smooth because it is prepared by hydrothermal process. Fe atom appear after HA is composited into MHA. The percent mass of Fe atom in MHA were 3:1, 2.5:1, 2:1, 1.5:1, at 34.5 %, 31.5 %, 27.7 %, and 24.4 %, respectively. The percent mass of Fe atom decreases in line with the VSM analysis which decreases the magnetization. The functional groups of HA and MHA are total acidity, carboxyl group, and phenolic hydroxyl group. The carboxyl and phenolic hydroxyl groups are iodized and interact with Fe2+ and Fe3+ from Fe3O4. However, the carboxyl group is more interactive with Fe3O4 than the phenolic hydroxyl group, so the carboxyl group’s reduction is very drastic. pHpzc of HA and MHA 3:1, 2.5:1, 2:1, 1.5:1 at 8.06, 5.82, 6.08, 4.80, and 4.76, respectively. HA and MHA were better at PSO and Langmuir model in adsorption of MB. Maximum adsorption capacity of HA and MHA 3:1, 2.5:1, 2:1, 1.5:1 at 66.225, 102.041, 161.290, 156.250, 138.889 mg/g, respectively. The highest maximum adsorption capacity is MHA 2.5:1 (161.290 mg/g). MHA 2.5:1 will be continued with regeneration. MHA regeneration efficiency decreased from 92.28 % to 58.92 % in the fifth cycle. These results indicate the good recyclability of MHA to remove MB supported by FTIR and XRD analysis after adsorption which shows no significant changes.