Comparative evaluation of lead and manganese removal from contaminated water using cocos nucifera shell powder in batch and continuous adsorption systems

• Coconut shell powder adsorbs Pb(II) and Mn(II) in batch and continuous systems. • Thermodynamic analysis shows higher affinity for Pb(II) than Mn(II). • Physical adsorption prevails, with chemical adsorption as the limiting step. • Coconut shell powder removes up to 93.1% Pb(II) and 85.7% Mn(II). • Further research needed on adsorbent regeneration and real wastewater tests. Even at low concentrations, lead and manganese ions in aquatic ecosystems pose significant risks to human health and the environment. Natural adsorbents offer a sustainable alternative to conventional heavy metal removal methods. This study aims to investigate the potential of coconut shell powder derived from Cocos nucifera agricultural waste as a sustainable biosorbent for removing Pb(II) and Mn(II) ions from aqueous solutions. The research focuses on evaluating the adsorption performance under batch and continuous flow conditions, analyzing the effects of key operational parameters, and characterizing the thermodynamic and kinetic behavior of the process. In the batch system, the effects of pH, particle size, Cocos nucifera concentration, and metal ion concentration were analyzed, while in the continuous system, the influence of flow rate and bed depth was evaluated to identify the key factors influencing adsorption efficiency. An atomic absorption spectrometer was used to determine the residual metal concentrations in solution. Maximum Pb(II) removal (98.8%) occurred at pH 3–8, with a particle size of 0.297–0.105 mm, an adsorbent dose of 4 g L⁻¹, and a Pb(II) concentration of 300 mg L⁻¹. For Mn(II), maximum removal (86.4%) was achieved at pH 7, with the same particle size range, an adsorbent dose of 6 g L⁻¹, and an Mn(II) concentration of 10 mg L⁻¹. Thermodynamic analysis confirmed a higher affinity for Pb(II) than for Mn(II), with values of 79.2 and 13.9 mg g −1 , producing a predominantly physical adsorption in monolayers. The adsorption process was rapid, reaching equilibrium within five minutes, as validated by pseudo-first and pseudo-second order kinetic models. Likewise, the maximum removals achieved in the continuous system were 85.7% and 93.1% for Pb (II) and Mn (II). Both batch and fixed-bed column results highlight Cocos nucifera as a promising low-cost biosorbent for Pb(II) and Mn(II) removal. However, further research is needed to evaluate ion competition, adsorbent regeneration, and performance in real effluent systems. These findings support the potential application of coconut shell powder in sustainable water treatment solutions.