Evaluation of Thermodynamic Parameters for Cu(II) Ions Biosorption on Algae Biomass and Derived Biochars

The removal of metal ions by biosorption on inexpensive materials is still a challenge for environmental engineering research. In this study, marine green algae biomass (Ulva lactuca sp.) and the biochars obtained from this biomass, at 320 ◦C (BC-320) and 550 ◦C (BC-550), were used as biosorbents for the removal of Cu(II) ions from aqueous solution. In addition to comparing the biosorption capacities, the determination of the thermodynamic parameters allows the choice of the most suitable material for the biosorption processes. The experimental results, obtained for Cu(II) ions biosorption on each biosorbent (algae biomass (AB), BC-320 and BC-550), at three different temperatures (10, 30 and 50 ◦C) were analyzed using Langmuir and Freundlich isotherm models, while pseudo-first order, pseudo-second order and intra-particle diffusions models were used to model the kinetic data. The biosorption of Cu(II) ions is best described by the Langmuir model and
the pseudo-second kinetic model, regardless of the type of biosorbent. Such behavior is characteristic
for the retention of metal ions on low-cost materials and is explained in the literature using the
concepts of molecular symmetry. The maximum biosorption capacity (qmax, mg/g) depends on the
temperature, but also on the type of biosorbent, and follow the order: BC-320 < AB < BC-550. Using
the experimental isotherms, the thermodynamic parameters (DG0, DH0 and DS0) for the biosorption
of Cu(II) ions on each biosorbent were calculated. The analysis of the obtained values constitutes the
main arguments for choosing BC-550 as the most effective biosorbent for the removal of Cu(II) ions
from aqueous media.