Evaluation of a magnetic coagulant based on Fe3O4 nanoparticles and Moringa oleifera extract on tartrazine removal: coagulation-adsorption and kinetics studies.

The lack of data regarding the mechanisms at work in the coagulation processes of different substances using magnetic coagulants makes it difficult to understand the phenomena involved and, consequently, makes it difficult to elucidate the mechanisms involved in the coagulation process. Thus, the present study aimed at evaluating the performance of a magnetic coagulant composed of iron oxide (Fe3O4) functionalised with Moringa oleifera (MO) salt extract in the treatment of a synthetic food industry wastewater simulated by the addition of dye to distilled water. From the data obtained in the coagulation/flocculation assays followed by magnetic sedimentation, the different mechanisms involved were evaluated for their fit to pseudo-first order, pseudo-second order, Langmuir and Freundlich theoretical models. The adjustments to the models were evaluated from the kinetic data and indicated that at pH 3 the best fit was to the pseudo-second order model, whereas for pH 6 and 9 the best fit was for the pseudo-first order model. The isothermal data were adjusted to the Langmuir model, suggesting adsorption of a monolayer, characterising chemical processes with selective adsorption. In relation to the mechanisms involved in the process, it is suggested that the neutralisation of charges was the predominant mechanism in the removal of tartrazine at pH 3, whereas at the other pH values evaluated the mechanism that prevailed was monolayer adsorption. Thus, the proposed magnetic coagulant was found to be an efficient alternative material for tartrazine removal, allowing easy separation in the sedimentation stage while also being compatible with environmental issues.