A novel green synthesis of MnO2-Coal composite for rapid removal of silver and lead from wastewater

Abstract

The presence of Ag(I) and Pb(II) ions in wastewater poses a significant threat to human health in contemporary times. This study aims to explore the development of a novel and economical adsorbent by grafting MnO₂ particles onto low-rank coal, providing an innovative solution for the remediation of water contaminated with silver and lead. The synthesized nanocomposites, referred to as MnO₂-Coal, underwent thorough characterization using FTIR, XRD, BET, and SEM to highlight the feasibility of in-situ surface modification of coal with MnO₂ nanoparticles. The adsorption of Ag(I) and Pb(II) from their respective aqueous solution onto MnO₂-Coal was systematically investigated, with optimization of key parameters such as pH, temperature, initial concentration, contact time, ionic strength, and competing ions. Remarkably adsorption equilibrium was achieved within a 10 min, resulting in impressive removal rates of 80-90 % for both Ag(I) and Pb(II) at pH 6. The experimental data were evaluated using Langmuir, Freundlich, and Temkin isotherm models. The Langmuir isotherm model proved to be more accurate in representing the adsorption of Ag(I) and Pb(II) ions onto MnO₂-Coal, exhibiting high regression coefficients (R² = 0.99) and maximum adsorption capacities of 93.57 and 61.98 mg/g, along with partition coefficients of 4.53 and 71.92 L/g for Ag(I) and Pb(II), respectively, at 293 K. Kinetic assessments employing PFO, PSO, Elovich, and IPD models indicated that the PFO and PSO models were most suitable for adsorption mechanism of Pb(II) and Ag(I) on MnO₂-Coal composites, respectively. Moreover, thermodynamic evaluation revealed the spontaneous and endothermic adsorption process for Ag(I), while exothermic behavior for adsorption of Pb(II). Importantly, this approach not only demonstrates cost-effectiveness but also environmental friendliness in treating heavy metal-contamination in water. The research suggests the potential of MnO₂-Coal composites as efficient and sustainable adsorbents for water purification applications.

Keywords: Adsorbent; Lead; MnO(2); Silver; Wastewater; low-rank Thar coal.