New derivatives of urea-grafted alginate for improving the sorption of mercury ions in aqueous solutions

International audienceChemically-modified alginate (obtained by grafting urea on alginate, with different ratios; alginate-urea (1:1) and its new derivatives alginate-urea (1:2) with an exceed of the percent of amino group by 7%) was successfully tested for mercury sorption in aqueous solutions. The influence of pH on metal sorption was first investigated: optimum pH was close to 5.5. Sorption isotherms were modeled using the Langmuir and the Sips equations, and sorption capacity slightly increased with the increased of the % of-NH 2 in the sorbent and the maximum sorption capacity exceeded 200 mg Hg l −1 (1.07 mmol Hg g −1 ; for alginate-urea (1:2)), this means two times the sorption capacity of reference material (i.e., nonmodified alginate), and also has a capacity improved compared to alginate-urea (1:1). Under selected experimental conditions the equilibrium was reached with 6-8 h of contact and the kinetic profiles were modeled using the pseudo-first order equation (PFORE), the pseudo-second-order rate equation (PSORE) and the resistance to intraparticle diffusion (RIDE). Surface functional groups, notably;-NH 2 ,-OH and-COOH, were involved in mercury sorption by alginate-urea, suggesting the ion exchange, complexation and/or electrostatic interaction of Hg(II) on the alginate-urea surface. The use of this material, environmentally friendly and simply obtained from a renewable resource, reveals promising for the treatment of low-metal concentration effluents: sorption capacities are comparable to alternative academic and commercials sorbents

Effective removal of nickel(II) and zinc(II) in mono-compound and binary systems from aqueous solutions by application of alginate-based materials

International audienceIn the present study, beads of alginate, alginate-biuret and alginate-urea, were synthesised for the removal of Ni(II) and Zn(II) metal ions from aqueous solution (in single and in the bimetallic component solution). The properties of the synthesised sorbents were investigated by pHpcz, ESEM-EDX and ESEM. The modelling of experimental data demonstrate that the PSORE equation fits well the kinetic profiles, while Langmuir and also Sips models correspond well to the results of sorption isotherms (heterogeneous surface). Also, the spontaneous of process and endothermic nature of sorption was demonstrated by thermodynamic study. The maximum sorption capacity of 3.22, 4.73 and 8.53 mmol g−1 was found for the beads of alginate, alginate-biuret and alginate-urea, respectively, in case of Ni(II) while it was 6.77, 6.97 and 7.14 mmol g−1 for alginate, alginate-biuret and alginate-urea, respectively, in case of Zn(II). It was found that at 0.3 mmol L−1 concentration, Zn(II) was selectively adsorbed while Ni(II) ions were concentrated/enriched in the solution in the case of alginate-urea, but alginate-biuret and alginate beads adsorbed almost the same amount of Ni(II) and Zn(II). In the bimetallic solution, the study of selectivity coefficients (KS) shows that the alginate-urea is a selective sorbent for Zn(II) and alginate-biuret for Ni(II) ions. Therefore, the two functionalised polysaccharides do not show the same harmony in front of the two-chemical species, thus, giving the possibility of their use as selective adsorbents in solutions containing these elements and can be used in applications of different interest