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

Abstract

Chemically-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., non-modified 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.

Keywords

• mercury recovery
• chemically-modified alginate beads
• urea-grafting
• sorption isotherms
• uptake kinetics
• multi-metal coexistenc