Study On The Preparation Of Hydrogel Sorbents And Their Adsorption Behavior For Heavy Metal Ions

With the rapid development of modern industry and urbanization,high emissions released and low resource utilization caused the increase of the environmental risks increasing dramatically.Massive emissions of the toxic heavy meta ls,like Cd,Pb and Cr,bring about serious environmental threats and serious hazards to human health.Present,most of major crises are associated with industrial effluent discharge.Consequently,the concentrations of heavy metals in effluent discharge must be strictly limited.Adsorption process has been regarded as one of the most effective techniques to remove heavy metal ions in wastewater.However,conventional sorbent materials are powerless to treat wastewaters with high metal concentrations to saf e level.To this end,a great deal of effort has been taken to explore new sorbent materials.Despite a certain degree of improvement in metal ions sorption capacity,for the practical application,there are three practical limitations:(1)slow kinetic,(2)loss of performance and(3)difficult separation.The slow near surface and internal diffusion rates of granular adsorbents seriously limit their overall kinetics Additionally,these adsorbents are easily subject to blocking and burial of surface sorpti on sites,resulting in serious loss of performance.Although nano-adsorbents possess good dynamics and high adsorption capacities,it is difficult to separate.The inefficient separation would result in high operation cost and secondary pollution.In this study,several new hydrogel adsorption materials are synthesized in order to remove and concentrate the heavy metal ions,and the adsorption performance of those hydrogel adsorption were researched in detail.The detailed novelties of this research can be categorized as following:(1)A sponge-like polysiloxane-graphene oxide(PS-GO)gel adsorbent for removing lead and cadmium from wastewater has been prepared by simple one-step sol-gel method.The maximum sorption capacity of Pb(?)and Cd(?)achieve as high as 256 mg/g and 137 mg/g.PS-GO gel adsorbent exhibits an excellent reusability because of its remarkable mechanical strength and highly efficient desorption/regeneration.In the static treatment process,after five cycles,Pb(?)in actual industrial effluent at 3.225 mg/L could be reduced to below 0.01 mg/L,still holding over 99% removal efficiency.Significantly,in the dynamic treatment process using a fixed-bed column packed with PS-GO gel,the treatment volume of wastewater is as high as 720 bed volume(BV)for Pb(?)and 480 BV for Cd(?)with producing only 11.31 m L eluent in each cycle.It should be stressed that the in situ regeneration of PS-GO gel adsorbent in fixed-bed column is operationally feasible and the treatment technology has the advantage of producing ‘‘zero'' amount of sludge.(2)A polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure.Due to the remarkable mechanical strength,the three-dimensional polyampholyte hydrogel could be fast separated,easily regenerated and highly reused.The sorption capacities were as high as 216.1 mg/g for Pb(?)and 153.8 mg/g for Cd(?)owing to the existence of the large number of active groups.The adsorption could be conducted in a wide p H range of 3~6 and the equilibrium fast reached in 30 min due to its excellent water penetration for highly accessible to metal ions.The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(?)and Cd(?)from actual industrial effluent to meet the regulatory requirements.The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes(BV)for Pb(?)and 200 BV for Cd(?).Furthermore,the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV for Pb(?)and 250 BV(8483 m L)for Cd(?),producing only 4 BV eluent.Compared with the traditional high density slurry(HDS)process with large amount of sludge,the proposed process would be expected to produce only a small amount of sludge.When the treatment volume was controlled below 209.3 BV,all metal ions in the actual industrial effluent could be effectively removed(<0.01 mg/L).(3)A new type of double-network hydrogel sorbent was developed to remove heavy metals in wastewater.The new sorbent could be conducted in a wide p H range of 2.5~7 and the equilibrium at a high innitial concentration of 120 mg/L fast reached in 45 minutes using a low adsorbent dosage of 1g/L due to its excellent water penetration for highly accessible to metal ions into its inner.The sorption capacity got to 256.4 mg/g for Cd(?)because of its porous network structure for making full use of adsorption active sites.Resultantly,even though Cd(?)concentration was as high as 180 mg/L,the Cd(?)could be entirely removed using as low as 1 g/L sorbent.All heavy metal ions in actual industrial effluent could be removed completely only with 4 g/L sorbent dosage.In the fixed-bed column experiments,the treatment volumes of the simulated effluent with a high Cd(?)concentration of 200 mg/L reached 2400 BV after eight cycles where the residual Cd(?)in effluent kept below 0.01 mg/L,producing only 48 BV eluent.Compared with traditional high-density slurry process with large amount of sludge,the proposed process would be expected to produce negligible amount of sludge.Furthermore,the desirable mechanical durability of the sorbent allowed easy separation and reusability.(4)A novel double-network hydrogel sorbent was well designed and prepared by a simple method using jute,acrylic acid and triethylene tetramine.The Jute/PAA gel shows the highly porous network structure,while the Jute shows blocky structure,which structures were easily subject to blocking and burial of surface sorption sites.The stability of the gel in water was investigated and the adsorption capacity of Jute/PAA gel and Jute for Pb(?)and Cd(?)were studied in detail.It found that the Jute/PAA gel could be conducted in a wide p H range than that of Jute,furthermore the Jute/PAA gel showed the strong adsorption ability to resist interference ions.The adsorption rate of the Jute/PAA gel is also faster than that of Jute and equilibrium fast reached in 10 min.In addition,the sorption capacities of Jute/PAA gel were as high as 5.8 mg/g for Pb(?)and 380 mg/g for Cd(?)at 303 K,while the sorption capacities of Jute for Pb(?)and Cd(?)were 77.1 mg/g and 62.5 mg/g at the same condition.With initial concentration up to 400 mg/L,after five cycle of adsorption,the Jute/PAA gel still showed a stable adsorption.