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–NH2 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; –NH2, –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.
Highlights
IntroductionThe bioaccumulation of metal ions in the food chain, their intrinsic toxicity for human and animal beings (with many health damages such as effects on nervous system, reproductive functions, skin, liver, etc) are the main reasons that can explain the increasingly strict recommendations on the discharge of industrial and domestic effluents
The bioaccumulation of metal ions in the food chain, their intrinsic toxicity for human and animal beings are the main reasons that can explain the increasingly strict recommendations on the discharge of industrial and domestic effluents
Biosorbents are processing through similar mechanisms to those involved in sorption processes: the functional groups at their surface, which are similar to those present on synthetic resins, may bind metal ions though chelation and ion-exchange mechanisms
Summary
The bioaccumulation of metal ions in the food chain, their intrinsic toxicity for human and animal beings (with many health damages such as effects on nervous system, reproductive functions, skin, liver, etc) are the main reasons that can explain the increasingly strict recommendations on the discharge of industrial and domestic effluents. A wide spectrum of processes exists for the recovery of metal ions from aqueous effluents, depending on managed flows, levels of concentration and market value of these metal resources Processes such as precipitation are frequently reported; the technical limitations (associated to the levels of residual concentration in function of the complexity of the solutions and presence of ligands), the poor selectivity that limits further metal valorization, and the production of huge amounts of contaminated sludge considerably. Biosorbents are processing through similar mechanisms to those involved in sorption processes: the functional groups at their surface, which are similar to those present on synthetic resins, may bind metal ions though chelation and ion-exchange mechanisms These materials can be used in their raw form but many studies have described the use of modified biopolymerbased sorbents, playing with the dual physical and chemical versatility of these materials. The presence of hydroxyl and/or amine groups on alginate and chitosan makes the material easy to chemically modify by grafting new reactive groups [22,23,24,25]
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