Equilibrium and kinetic study of Zn(II) ions biosorption on algae biomass and derived biochar

Abstract

Removal of heavy metal ions from industrial effluents prior to discharge is still and important issue for environmental protection and biosorption can be a solution. That is why the use of low-cost materials in biosorption processes is a viable alternative which must be considered. In this study, two such materials, namely algae biomass (Ulva lactuca sp.) and the biochar obtained from this biomass, were examined as potential biosorbents for the removal of Zn(II) ions from aqueous solution. At an initial solution pH of 5.0 and 4.0 g biosorbent /L, the removal efficiency of Zn(II) ions is up to 63 % for marine algae biomass and up to 94 % for algae biochar, after 180 min of contact time and room temperature (22 ±1 °C). The equilibrium and kinetic modelling of the obtained experimental results have shown that biosorption process on both biosorbents follow Langmuir model (R²> 0.99) and pseudo-second order kinetic model (R²> 0.999). The maximum biosorption capacity, calculated from Langmuir model, was 2.1 time higher in the case of algae biochar than in the case of algae biomass, while the kinetics of the biosorption process on algae biomass is faster (k₂ = 0.1118 g/mg min) that the algae biochar (k₂ = 0.0353 g/mg min). The functional groups involved in the Zn(II) ions retention and the morphological changes during biosorption were analyzed using FTIR spectra and SEM microscopy, for both biosorbents. Based on this study, algae biomass and algae biochar have proved to have high efficiency for removing Zn(II) ions from aqueous media, and can be employed in decontamination processes at large scale.