Preparation Of Immobilized Modified Yeast Adsorbent And Its Adsorption For Cr(Ⅵ) In Water

With the rapid development of modern industries,metallic waste-water discharge has caused severe environment pollution,thus posing a serious threat to human being and environment.The extensive use of hexavalent chromium,Cr(Ⅵ),and chromium compounds in industrial field could result in negative impact such as poisoning,once the concentration of Cr(Ⅵ)is over 0.1 mg/L.Therefore,waste-water treatment for the removal of Cr(Ⅵ)is of great significance.This paper discussing the synthesis of composite sorbents with different shapes and structures,in which yeasts are the functional component.Before the preparation,yeast was modified by means of methlyation modification method.Several composite materials were successfully fabricated,including calcium alginate/gelatin immobilized methylated yeast composite beads,methylaed yeast/gelatin spongy composite and the methylated yeast/cellulose composite membrane.Moreover,adsorption properties of Cr(Ⅵ)ions on modified-yeast based composite sorbents were also investigated.Using alginate/gelatin as matrix,methylated yeast was immoblized by dropping method to fabricate composite beads.The synthesized immobilized beads were subjected to the removal of Cr(Ⅵ)from aqueous solution.Static adsorption experiment was carried out to study the effects of adsorption conditions towards adsorption efficiency on Cr(Ⅵ).The optimum condition were: contact time 180 minutes,temperature 30℃,pH 2.0,beads dose 0.05 mg/ml.Under this condition,the adsorption of Cr(Ⅵ)on the beads exhibited a maximum value of 18.36 mg/g.Adsorption kinetics model and isotherm adsorption model were used to simulate the adsorption process.It was found that the Quasi-second-order model described the adsorption kinetics data well and the adsorption isotherm obeyed the Freundlich isotherm.Additionally,Fourier transform infrared(FTIR),scanning electron microscopy(SEM)were adopted to characterize the composite beads.FTIR results showed that functional groups(such as the hydroxyl group,amino group,etc.)onyeasts and the matrix presented great influence on the adsorption efficiency.SEM analysis indicated that modified yeast granules well dispersed in composite substrate.Spongy composite materials were prepared by embedding methylated yeast into gelatin matrix through free-drying treatment,and were used for the removal of Cr(Ⅵ)from aqueous medium.Effects of conditions on adsorption efficiency were studies by static experiments.The maximum adsorption capacities of the spongy-like sorbents were found to be 19.40 mg/g.The optimum conditions were: contact time 180 minutes,temperature 30℃,pH 2.0,sorbent dose 0.05 mg/mL and the quality ratio of methylated yeast and gelatin was 3:1.Furthermore,results also showed the adsorption process could be well fitted by both Quasi-second-order kinetics model and Freundlich isotherm model.SEM observation depicted that the methylated yeast was embedded in gelatin substrate and the three-dimentional porous structure of the composite was observed.Cellulose/methylated yeast composite membranes were also successfully fabricated by freeze-drying treatment.The optimum experimental parameters obtained from static adsorption experiment were as follows: contact time 180 minutes,temperature 30℃,pH 2,sorbent dose 0.05 mg/mL and the quality ratio of methylated yeast and cellulose was 6:1.Under this circumstances,maximum adsorption capacity was 18.04 mg/g.The adsorption process of composite membrane could also be fitted by both Quasi-second-order kinetics model and Freundlich isotherm model.SEM results indicated that modified yeast granules evenly dispersed in the cellulose substrate so that the membrane is more effective for adsorption.Study shows that different adsorbing materials with different structures and properties can be developed using different polymer matrix as substrate to immobilize methylated yeast.Moreover,these composite materials have a wide range of sources,low cost and good adsorption properties.This study provides reference and new materials for the enrichment and treatment of Cr(VI)waste-water,which has potential application prospects.