Adsorptive Removal of Heavy Metal Ions from Industrial Wastewater Using Low-Cost Bio-Adsorbents

Abstract

Industrial effluents from electroplating, metal finishing, battery, mining and related sectors may contain persistent heavy metal ions that cannot be destroyed by conventional biological treatment. This methodology paper presents a laboratory-scale comparative framework for removing Pb(II), Cu(II), Cd(II) and Zn(II) using low-cost bio-adsorbents prepared from rice husk, banana peel, spent tea waste and sawdust. The proposed procedure includes washing, drying, particle-size control, physicochemical characterization, batch adsorption tests, atomic absorption spectrometric analysis, adsorption-equilibrium modelling, kinetic evaluation and adsorbent regeneration. The principal factors examined are solution pH, adsorbent dosage, contact time and initial metal concentration. Removal efficiency and equilibrium adsorption capacity are calculated from initial and residual metal concentrations, while Langmuir/Freundlich isotherms and pseudo-first-/pseudo-second-order kinetic models are used to interpret uptake mechanisms. Literature available up to 2018 indicates that lignocellulosic and fruit-waste sorbents can provide substantial metal uptake because hydroxyl, carboxyl, phenolic and other oxygen-containing groups participate in ion exchange, electrostatic attraction and surface complexation. The proposed design emphasizes inexpensive raw materials, standardized operating conditions and regeneration testing so that the most promising biosorbent can be identified for subsequent evaluation with real industrial wastewater. Reported numerical values in the results section are literature benchmarks or planning targets rather than newly generated experimental measurements.