Application and regeneration of magnetic material MgAlLDH@Fe3O4 humic acid with removal capacity for malachite green

Malachite green (MG), a dye in wastewater, pollutes the natural environment, and it is difficult to eliminate dyes from aquatic systems. MgAlLDH-magnetite humic acid (Mg3Al@M2HA) was prepared for MG adsorption via coprecipitation and hydrothermal methods. The adsorption was performed using the batch adsorption method at the pH of the point of zero charge (8.33), with an optimum contact time of 120 min and a maximum concentration of 100 mg/L of MG. Furthermore, the pseudo-second-order and Langmuir models were better fitted to the kinetic and isotherm models, respectively. The maximum monolayer adsorption capacity for MG on Mg3Al@M2HA at 313 K was 113.6 mg/g. The calculated thermodynamic parameters ($\Delta$ H = 18.524 kJ/mol, $\Delta$ S = 0.076 J/Kmol, $\Delta$ G =  − 4.586 to − 6.111 kJ/mol) implied that the MG adsorption was spontaneous, endothermic, and had degrees of randomness in the temperature range of 303–323 K. Moreover, the ΔH was less than 40 kJ/mol, confirming that the combination of MG with Mg3Al@M2HA was due to the physisorption with electrostatic interaction, hydrogen bonding, and π–π interaction. Recycling experiments showed that the MG removal rate was 82.55 % after 5 cycles. This study provides new insights into Mg3Al@M2HA and its potential applications for MG adsorption.