Abstract
Batch sorption studies were conducted to assess the potential of a phosphonated silica polyamine composite (BPAP) to remove metals (Co, Cu, Fe, Mg, Mn, Ni, U and Zn) from mine waters. The metal adsorption showed a good Langmuir isotherm fit. Ni and Mn fitted both the Freundlich and Langmuir isotherms. The activation energies (Ea) of Co, Mg and Ni ranged between 5 and 40 kJ∙moℓ-1, signifying physisorption while U showed a chemisorption type of adsorption (with Ea > 50 kJ∙moℓ-1). Cu and Fe on the other hand gave negative Ea values, indicating their preference to bind to low-energy sites. The pseudo-second-order kinetic model provided the best correlation of the experimental data, except for Mg and Ni for which the pseudo-first-order model and the Elovich model gave a better fit, respectively. Adsorption was almost constant over a wide pH regime and increased with time. Adsorption increased with concentration of the metals with the exception of Co, Fe and Ni which displayed about a 40% drop at a concentration of 200 mg∙ℓ-1. Desorption experimental data gave poor results except for U which showed 99.9% desorption.Keywords: silica polyamine composite, sorption, kinetics, isotherms, desorption
Highlights
The presence of trace metals in aquatic systems is of concern because of their toxicity and non-biodegradable nature
This study presents a silica-based polyamine composite, namely BPAP, as an alternative material for the adsorption of metals from acidic mine leachates and wastewaters
This study focused on the kinetic, equilibrium and thermodynamic processes related to metal sorption on BPAP, using metals commonly found in acid mine drainage (AMD)
Summary
The presence of trace metals in aquatic systems is of concern because of their toxicity and non-biodegradable nature. = k1 (qe – qt) where: qe and qt are the amount of metal ions adsorbed (mg∙g-1) at equilibrium and at any time t, respectively k1 is the rate constant (min-1) of pseudo-first-order adsorption. Where: qt is the amount of metal ion adsorbed at time t (min) expressed (mg∙g-1), kid is the initial rate constant (mg∙g-1∙min-1/2) of intraparticle diffusion, t is the time of sorption duration (min), and C gives information about the boundary layer thickness
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