Kinetic and Isotherm Equations to Calculate the Biosorption of Lead (Pb²⁺) Ions from Aqueous Solutions by Pseudomonas spp

• Ameer Sadiq Kareem1, Sarah Muayad Bahjat2, Mais Mahmoud Khamas3, Shuruq Khalid Yassin4, Aya Majeed Abdulsalam5

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Lead (Pb²⁺) contamination of water resources poses serious environmental and human health risks, and conventional physicochemical treatment methods are often costly and generate secondary waste. This study evaluated the biosorption of Pb²⁺ ions from aqueous solution using Pseudomonas spp. biomass as a low-cost, eco-friendly biosorbent. Batch kinetic experiments were carried out over 5–60 min at an initial Pb²⁺ concentration of 30 mg L⁻¹ (298 K, 100 rpm), and equilibrium isotherm experiments were performed over an initial concentration range of 5–30 mg L⁻¹ at 318 K. Kinetic data were analyzed using the pseudo-first-order (PFO) and pseudo-second-order (PSO) models, while equilibrium data were fitted to the Langmuir and Freundlich isotherms. The adsorption kinetics were best described by the PFO model (R² = 0.936; k1 = 0.1408 min⁻¹; qe = 136.55 mg g⁻¹), indicating a physisorption-controlled mechanism dominated by film diffusion, whereas the PSO model showed a much weaker fit (R² = 0.594). Equilibrium data deviated strongly from the Langmuir model (R² = 0.1631) but fitted the Freundlich model well (R² = 0.8215; KF = 3.58; 1/n = 0.89), consistent with a heterogeneous bacterial surface bearing multiple binding-site energies. The maximum theoretical Langmuir capacity was 149.25 mg g⁻¹, with a favorable separation factor (RL = 0.60–0.90). These results indicate that Pseudomonas spp. is an effective, low-cost biosorbent for Pb²⁺ removal from contaminated water and is a promising candidate for sustainable wastewater treatment applications.

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