Efficient malachite green dye removal from wastewater using activated Casuarina equisetifolia cones and needles adsorbents: characteristics, adsorption kinetics, thermodynamic modeling, and column test

Changing the surface of sorbents has become crucial for increasing the adsorbent’s effectiveness. Thermal changes can boost the adsorption capability of green sorbents. In this study, the cones and needles of the Casuarina equisetifolia (CE) were thermally activated and used in the adsorption of malachite green from the water system. Activated CE was characterized using Brunauer–Emmett–Teller, zeta potential, point of zero charge, scanning electron microscopy, and energy dispersive X-ray to analyze morphological, physical, and chemical behavior after surface modification and after adsorption. The specific surface area for the activated Casuarina equisetifolia cones (CEC) and needles (CEN) was 533.393 and 736.59 m2 g−1. The effects of variables were examined at an agitation speed of 240 rpm. The optimum parameters, including pH, time, dosage, and temperature, were found to be pH 12, 40 min, 0.2 g, 50 °C for CEN and pH 12, 20 min, 0.1 g, 50 °C for CEC. The adsorption data were fit to Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. Freundlich provided the best fit with the experimental data (R2 is 0.9955 and 0.9832 for CEN and CEC), with a maximum adsorption capacity of 26.091 mg g−1 for CEN and 49.521 mg g−1 for CEC. From the kinetics study, pseudo-second-order was suggested with R2 > 0.99. A fixed-bed column experiment was conducted to evaluate the dynamic adsorption performance. The obtained total bed capacity was 757.48 mg (equivalent to 9.07 mg g−1) at breakthrough time 300 min and exhaustion time 460 min.