Removal of Environmentally Polluting Heavy Metal Ions from Industrial Wastewater Using Rice Husk

This study examined economical and accessible adsorbents. Lead (Pb), nickel (Ni), and cadmium (Cd) were removed from a wastewater-simulated aqueous solution by batch adsorption. Rice husk’s qualities were assessed using FTIR, SEM, EDS, and BET analysis. pH levels of 2–10, contact times of 30–180 min, agitation speeds of 100–300 rpm, temperatures of 20–40 °C, adsorbent doses of 0.5–2.5 g, heavy metal ion concentrations of 100–800 parts per million, and particle sizes of 75–850 µm, all of which affect heavy metal ion removal, were examined. The study found that lead is adsorbed best at a pH of 5, while nickel and cadmium are best adsorbed at a pH of 6; 150 min were sufficient to equilibrate all metal ions. Maximum removal was observed at a rotation speed of 200 revolutions per minute, a temperature of 25 °C, heavy metal ion concentrations of 100 parts per million, and a particle size of 75 µm. Adsorption kinetics, thermodynamics, and isotherm adsorption models were studied after experimental data collection, and ion exchange equilibrium data were analyzed using the Langmuir and Freundlich isotherm models. Rice husk’s adsorption of Cd+2, Ni+2, and Pb+2 was predicted by the Freundlich model, and Cd+2, Ni+2, and Pb+2 had R2 values of 0.99825, 0.98921, and 0.9851, respectively. The negative enthalpy change ( \(\Delta {\text{H}}\) ) and decreasing thermodynamic equilibrium coefficient (kd) occurring as temperature (T) decreases make the process exothermic.