Understanding the removal and regeneration potentials of biogenic wastes for toxic metals and organic dyes

• Pragmatic survey of the surface characteristics of indigenous biogenic wastes (Pentaclethra macrophylla and M. alnifolia biosorbents) for some pollutants.
• Insights into the adsorption dynamics, equilibrium and thermodynamics for the removal of some toxic metal ions and organic dyes.
• Useful insights into the adsorption capacities of low cost and locally sourced biogenic wastes (P. macrophylla and M. alnifolia biosorbents) for some pollutants.
• Chemical regenerative approach for biogenic wastes; A desorption perspective.

This work highlights the removal dynamics of some industrial dyes, such as Congo Red (CR) and Methylene Blue (MB), Cd2+ and Pb2+ by two low-cost and readily available tree wastes (Pentaclethra macrophylla tree bark (PMTB biosorbent) and Malacantha alnifolia   tree bark (MATB biosorbent). In this research work, experimental variables such as pH, biomass dose, initial solute ion concentration, agitation time and temperature were optimised. The surface textures of PMTB and MATB biosorbents were characterised using pH of Point of Zero Charge (pHPZC), Fourier Transform Infra Red Spectroscopy (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. Proximate Analysis (PA) and Bulk Density (BD) of these biosorbents were also determined. The highest Langmuir saturation monolayer adsorption capacity, qmaxLqmaxLfor the removal of CR by MATB biosorbent was obtained as 800.00 mg/g. The pseudo-second order model provided the best fit for the kinetic data obtained for the removal of CR, MB, Cd2+ and Pb2+ by PMTB and MATB biosorbents. This implied that chemisorption might be the mechanism of the solute ions–biosorbents interaction in this study. Weber–Morris intraparticle diffusion model showed that intraparticle diffusion was not the only rate limiting step of the adsorption processes. Film/pore diffusion process might have played an important role in the rate limiting step of the adsorption processes. Thermodynamic data indicated that (ΔG°) for the removal of CR, MB, Cd2+ and Pb2+ onto PMTB and MATB biosorbents were non spontaneous at all temperatures. Also, (ΔH°) and (ΔS°) for the removal of CR, MB, Cd2+ and Pb2+ onto the biosorbents depicted the adsorption processes being exothermic with decreasing of the chaos.

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