A review on the use of lignocellulosic materials for arsenic adsorption

In this review, bibliometric analysis was made of recent studies and current trends concerning the application of lignocellulosic materials as bioadsorbents for the removal of arsenic from aqueous systems. Evaluation was made of lignocellulosic adsorbents and their chemical characteristics, as well as interactions involved in the adsorption of arsenic, bioadsorbent reusage (desorption and re-adsorption), competition between co-existing ions in multi-element aqueous solutions, and applications of bioadsorbents in batch and continuous systems. Lignocellulosic biomass has been shown to be a promising source of new adsorbents, since it is a low-cost and renewable material. However, there seems to be no commercially available technology that uses bioadsorbents based on lignocellulosic biomass for arsenic removal. In addition, the structural modification of lignocellulosic biomass to improve its adsorption capacity and selectivity has proved to be a suitable strategy, with the service time and the selectivity of the bioadsorbent in the presence of co-existing ions the most critical aspects to be pursued. The competitive adsorption of co-existing anions (PO₄^3-, SO₄^2-, NO₃^-, and Cl^-) by the adsorption sites, as well as life-cycle assessment and cost analysis are rarely reported. Complexation, electrostatic attraction, ion exchange and precipitation were the main interactions involved in the adsorption of arsenic on lignocellulosic materials. However, most studies have failed to prove the nature of the interactions. Macroscopic methods can be useful to evaluate the adsorption mechanism of arsenic on bioadsorbents of complex structure, such as lignocellulosic biomass (modified or not). Nevertheless, the elucidation of the adsorption mechanism requires experiments based on measurements at the microscopic level. The upscaling of biosorption technology for arsenic removal will only be possible through studies that investigate: i) the interactions involved in the adsorption process; ii) the transfer of bench-scale experiments to pilot-scale experiments with real contaminated water with low arsenic concentration; and iii) the life-cycle assessment of biosorbents produced from lignocellulosic biomass.

Biosorption of metal ions using a low cost modified adsorbent (Mauritia flexuosa): experimental design and mathematical modeling

Buriti fibers were subjected to an alkaline pre-treatment and tested as an adsorbent to investigate the adsorption of copper, cadmium, lead and nickel in mono- and multi-element aqueous solutions, the results showed an increase in the adsorption capacity compared to the unmodified Buriti fiber. The effects of pH, adsorbent mass, agitation rate and initial metal ions concentration on the efficiency of the adsorption process were studied using a fractional 2(4-1) factorial design, and the results showed that all four parameters influenced metal adsorption differently. Fourier transform infrared spectrometry and X-ray fluorescence analysis were used to identify the groups that participated in the adsorption process and suggest its mechanisms and they indicated the probable mechanisms involved in the adsorption process are mainly ion exchange. Kinetic and thermodynamic equilibrium parameters were determined. The adsorption kinetics were adjusted to the homogeneous diffusion model. The adsorption equilibrium was reached in 30 min for Cu(2+) and Pb(2+), 20 min for Ni(2+) and instantaneously for Cd(2+). The results showed a significant difference was found in the competitiveness for the adsorption sites. A mathematical model was used to simulate the breakthrough curves in multi-element column adsorption considering the influences of external mass transfer and intraparticle diffusion resistance.