Isotherm, Kinetic and thermodynamic investigation on the biosorptive removal of Pb (II) ion from solution onto biochar prepared from breadfruit seed hull

Abstract

This study investigates the adsorption of lead(II) ions from aqueous solutions using biochar derived from breadfruit seed hulls, addressing the growing concern of lead contamination in water due to its toxic effects on human health and the environment. The aim of the study was to assess the efficiency of breadfruit seed hull biochar in removing lead ions, with a focus on understanding the adsorption mechanisms and the influence of key parameters. Batch adsorption experiments were conducted, examining the effects of solution pH (2.0–11.0), initial lead concentration (10–50 mg/L), temperature (300 K to 323 K), and adsorbent dosage (0.02–0.1 g). The results showed a significant increase in removal efficiency from 50% to 84.5% as the pH rose from 2.0 to 11.0, with the highest removal occurring at pH 11.0, though pH 6.0 was selected as the optimal condition to minimize the formation of metal hydroxides. Removal efficiency decreased from 83% to 47.6% as the initial lead concentration increased from 10 mg/L to 50 mg/L. Temperature also positively impacted the adsorption, with the removal percentage increasing from 72.5% to 82% as the temperature rose from 300 K to 323 K, suggesting an endothermic adsorption process. The adsorption capacity increased from 4.2 mg/g to 11.9 mg/g with the rise in lead concentration. The Langmuir model provided the best fit for the adsorption data, with a high coefficient of determination (R² = 0.99595) and a separation factor (RL) ranging from 0.1 to 0.41, indicating favourable adsorption. The Freundlich model also indicated favourable adsorption with an n value of 2.622, though it showed a lower fit compared to the Langmuir model. The study concluded that breadfruit seed hull biochar is an effective biosorbent for lead removal, with the adsorption process primarily governed by monolayer adsorption and chemisorption. It is recommended that breadfruit seed hull biochar be considered for water treatment applications targeting heavy metal removal, with further research into its regeneration and large-scale application for environmental cleanup.