Synthesis of sulfonated metal-substituted hydroxyapatite and its polymeric composite for sequestration of lead and cadmium from water: Batch and column study.

Abstract

Aluminium substituted hydroxyapatite (aHAp) was functionalized with sulfonate moieties employing an in-situ co-precipitation method using thioglycolic acid (TGA). Polymeric composite beads (denoted as aHAp-TGA PAN) were synthesized by immobilizing the modified aHAp (aHAp-TGA) nanoparticles in polyacrylonitrile (PAN) matrix for removal of toxic heavy metals, lead (Pb) and cadmium (Cd), from water. The adsorbents (both nanoparticles and composite) were characterized using state-of the art techniques. aHAp-TGA demonstrated a maximum saturation capacity of 1131 mg/g and 177 mg/g for Pb and Cd, respectively, evidencing significant increase in capacity (nearly 40 % for Pb and over 60 % for Cd) compared to aHAp due to the inclusion of sulfur-functionalities into the structure (through chelation and electrostatic interaction). The influence of adsorbent dose, pH, feed concentration, temperature and contact time were explored in detail along with the associated kinetic and thermodynamic parameters. High affinity of aHAp-TGA for Pb and Cd was indicated by the distribution coefficient (Kd:3.66 × 10⁵ mL/g and 1.25 × 10⁴ mL/g, respectively). The selectivity in presence of interfering ionic species and the regeneration of the materials (for 5 cycles) were also observed. Dynamic uptake studies were conducted in adsorption column with aHAp-TGA PAN beads to study the breakthrough performance that was simulated using an available diffusion-adsorption-convection model. This work focuses on the efficient wastewater treatment using the macrobeads showcasing a sustainable and scalable media in real-field application.