Adsorption of Thorium(IV) from Aqueous Solutions Using Magnetic Casuarina equisetifolia Needles

The contamination of aquatic environments by radioactive heavy metals, particularly thorium (Th(IV)), represents a major environmental challenge due to the expansion of mining and nuclear-related activities. This study investigates the potential of a magnetic biosorbent prepared from Casuarina equisetifolia needles for the removal of Th(IV) from aqueous solutions through a liquid–solid adsorption process.

The biosorbent was obtained by magnetizing powdered Casuarina equisetifolia needles with Fe₃O₄ nanoparticles synthesized via chemical co-precipitation. The material was characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA/DTG), and point of zero charge (pHpzc) determination, confirming the successful incorporation of magnetic nanoparticles.

Batch adsorption experiments were conducted to evaluate the effects of pH, adsorbent dosage, contact time, initial thorium concentration, ionic strength, and temperature. The optimum conditions were achieved at pH 3.3, using 0.01 g of biosorbent and an equilibrium time of 30 min, resulting in a removal efficiency of 80%.

The adsorption process followed the pseudo-second-order kinetic model (R² = 0.9995), while the Langmuir isotherm provided the best fit (R² = 0.9945), with a maximum adsorption capacity of 61.73 mg g⁻¹. Thermodynamic analysis indicated that the adsorption process is spontaneous and endothermic. These findings demonstrate that magnetic Casuarina equisetifolia needles constitute an efficient, low-cost, and environmentally friendly biosorbent for thorium removal from contaminated water.