Abstract
Alginate and algal-biomass (Laminaria digitata) beads were prepared by homogeneous Ca ionotropic gelation. In addition, glutaraldehyde-crosslinked poly (ethyleneimine) (PEI) was incorporated into algal beads. The three sorbents were characterized by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX): the sorption occurs in the whole mass of the sorbents. Sorption experiments were conducted to evaluate the impact of pH, sorption isotherms, and uptake kinetics. A special attention was paid to the effect of drying (air-drying vs. freeze-drying) on the mass transfer properties. For alginate, freeze drying is required for maintaining the porosity of the hydrogel, while for algal-based sorbents the swelling of the material minimizes the impact of the drying procedure. The maximum sorption capacities observed from experiments were 415, 296 and 218 mg Pb g−1 and 112, 77 and 67 mg Cu g−1 for alginate, algal and algal/PEI beads respectively. Though the sorption capacities of algal-beads decreased slightly (compared to alginate beads), the greener and cheaper one-pot synthesis of algal beads makes this sorbent more competitive for environmental applications. PEI in algal beads decreases the sorption properties in the case of the sorption of metal cations under selected experimental conditions.
Highlights
For the last few decades, the regulations for metal content in drinking water and concerning the permissible levels for their discharge into the environment have been seriously reinforced making the control of metal concentration in the industrial effluents a challenging issue for Industry
Improvements of sorption properties for Zn(II), Cd(II) and Cu(II) in complex system (in the presence of Na(I), K(I) or Ca(II)) by glutaraldehyde-crosslinked PEI immobilized in alginate matrixes [44], and for Cu(II), Zn(II) and Ni(II) by tannic acid-grafted PEI encapsulated in alginate beads [45] have already been found
An on-going rese8aorcf h21 performed in parallel to the present study has shown that the incorporation of PEI in algal beads aslulobwstsansutibalsltyanintciarlelaysincgrtehaesisnogrpthtieonsocrapptaiocnitycaopf athcietymoaftethriealmfoartemrieatlafloarnmioentsasl uacnhioanssPsdu(cIhI) aosr Pdt((IIVI)) othr aPtt(fIoVrm) tshacthlfoorrom-asnciohnlosroin-anHiConl ssoinluHtioCnlss. oIlnudtieoends,. inIntdheisedc,asine thies ccoamseptohseitecosmorpboesnites scoanrbebnintsd ctaentrabcihnldortoetpraalclhadloartoepaalnlaiodnaste aanndionhsexanacdhhloerxoapclhaltoinroatpelaatinniaotnesanoinonps roontopnraotteodnaatemdinaemignreougprosupbsy beyleeclteroctsrtoastitcataicttarattcrtaioctnioonnopnrportontoanteadtedamaminienegrgoruopuspsofofPPEEI Iccoommppoouunndd((oorr iioonn exchange with tthhee ccoouunntteerraanniioonnbboouunnddttoopprroottoonnaatteeddaamminineeggrroouuppss).)
Summary
For the last few decades, the regulations for metal content in drinking water and concerning the permissible levels for their discharge into the environment have been seriously reinforced making the control of metal concentration in the industrial effluents a challenging issue for Industry. This, in turn, makes the beneficial utilization of algae limited by the difficulty in recovering and collecting these biosorbent particles after the sorption process In addition these materials are generally difficult to use in conventional fixed-bed column systems due to head loss and clogging effects. Improvements of sorption properties for Zn(II), Cd(II) and Cu(II) in complex system (in the presence of Na(I), K(I) or Ca(II)) by glutaraldehyde-crosslinked PEI immobilized in alginate matrixes [44], and for Cu(II), Zn(II) and Ni(II) by tannic acid-grafted PEI encapsulated in alginate beads [45] have already been found The incorporation of this high-density amine-bearing compound in alginate or algal capsules is supposed to introduce supplementary reactive groups with the objective to extend the range of pH in which the sorbent can be used, to enhance sorption capacities and improve sorption selectivity. It is noteworthy that these sorbents were designed and applied for the pre-treatment of metal-bearing solutions and not for the purification of aqueous streams to reach drinkable levels
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