Untreated Mining Influenced Water Sludge (MIWS) for Lead Adsorption: Modelling Mass Transfer Effects

Contamination of water sources by heavy metals, such as lead, presents a significant environmental challenge. This study explored the kinetics of adsorption using a novel industrial waste by-product, mining influenced water sludge (MIWS), for the adsorption of lead in aqueous solutions. By varying agitation speeds – 150, 200 and 250 rpm – and average particle diameters – 1, 2 and 3 mm – the impact of external mass transfer effects and internal mass transfer effects was studied. It was observed that varying average adsorbent particle diameters had an impact on the adsorption kinetics, particularly regarding the time required to achieve equilibrium and maximum Pb(II) removal efficiency. At set conditions – same initial Pb(II) concentration, temperature, adsorbent dosage, and adsorbate solution pH – adsorption kinetics were notably faster for 1 mm adsorbate particles compared to 3 mm particles, requiring only half the time to reach equilibrium. The longer contact time required to reach equilibrium indicates the impact of internal mass transfer effects. Crank’s mass transfer model was used to quantify the effective diffusivity, providing operational parameters required for continuous process design. This research offers a sustainable remediation option by valorising an untreated waste sludge that can ideally be utilised in continuous flow processes, contributing to environmentally sound water treatment practices by lowering production energy requirements and reducing emissions.