Abstract:
Rapeseed seeds are one of the most important categories of raw materials used to obtain
biofuels. However, the biomass resulting after oil extraction is still considered waste, for which
valorization solutions are sought. In this study, we propose the use of this type of residual biomass
(rapeseed waste biomass (RWB)) as a biosorbent for the removal of toxic metal ions from aqueous
media. Two toxic metal ions were selected for the experimental studies, namely: Pb(II) and Hg(II).
The optimal biosorption conditions, for both metal ions, were selected based on response surface
methodology and were verified experimentally in batch systems. More than 92% of the initial amount
of Pb(II) and Hg(II) are retained under the following conditions: pH = 6.5 for Pb(II) and 4.0 for Hg(II);
biosorbent dosage = 4.0 g/L; contact time = 3 h; temperature = 25 1 C. Isotherm (Langmuir, Freundlich
and Temkin models) and kinetic (pseudo-first order, pseudo-second order and intra-particle
diffusion models) modelling of the experimental data were used for the quantitative evaluation of
both biosorption processes. Although the Langmuir maximum biosorption capacities are different
(higher in the case of Pb(II) (61.97 mg/g) than in the case of Hg(II) (51.32 mg/g)), the pseudo-second
order kinetic constants have the same order of magnitude. This shows that the retention of both
metal ions involves similar elementary steps and that RWB behaves as a typical biosorbent. These
characteristics, together with the very good desorption behavior, provide a complete picture of the
possible applications of this waste in environmental decontamination processes.
