Chitosan-supported Hydrous Ferric Oxide Hydrogel Beads For Adsorption Of Arsenite From Aqueous Solution

Groundwater arsenite [As???] pollution is a global environmental issue,which has high toxicity and bioaccumulation,serious threat to human health and ecological environment.As???removal by adsorption method has advantages of low cost and high efficiency,becoming more and more popular among environmental scientists.Hydrous ferric oxide?HFO?is an effective and cheap adsorbent for As???removal,but the powdered HFO unfavorable to solid-liquid separation and application in column adsorption.Chitosan?CS?-based HFO adsorbent has received wide attention in recent years.Unfortunately,previous research showed that iron-loaded amount of CS-based HFO adsorbent is low and adsorption performance of As???is not ideal.In the paper,preparation of millimeter-sized entrapment of HFO in chitosan hydrogel beads?CS/HFO?and chitosan-Fe3+ hydrogel beads?CS-HFO?by the methods of subject-object encapsulation and homogeneous-precursor,respectively.The procedure with oven-drying and vacuum freeze-drying were used to produce four kinds of adsorbent materials,namely oven-dried CS/HFO?OD@CS/HFO?and freeze-dried CS/HFO?FD@CS/HFO?,oven-dried CS-HFO?OD@CS-HFO?and freeze-dried CS-HFO?FD@CS-HFO?.Then aforementioned four adsorbents were characterized by XRD,SEM,FTIR and XPS;A systematic study on the adsorption properties of As???removal were studied,including adsorption kinetics,adsorption isotherm,solution p H,additive dosage and competition effects;The recyclability of adsorbents were studied and column adsorption performance with simulated As???-containing groundwater were evaluated;Finally,As???adsorption mechanism were discussed.Research achievements are of realistic significance for groundwater arsenic remediation.Main conclusions are as follows:?1?Characterization results showed that HFO in four kinds of adsorbents were amorphous in nature;structure of oven-dried adsorbents materials were compact,while the interior of freeze-dried adsorbents were porous structure,and honeycomb-like structure appeared in the FD@CS-HFO prepared by homogeneous-precursor method;Compared with oven-dried adsorbents,specific surface area of freeze-dried adsorbents increased;HFO distribution of interior of adsorbents prepared by homogeneous-precursor method were more uniform than adsorbent prepared by subject-object encapsulation method.?2?Batch adsorption As???experiment showed that the four kinds of adsorbents had a relatively stable applicability in p H 4-9 range;Initial adsorption rate increased with rising temperature,but rising temperature had no significant effect on As???adsorption equilibrium time and adsorption quantity;Adsorption ability of freeze-dried materials for As???is better than that of oven-dried materials,maximum adsorption capacity of FD@CS/HFO and FD@CS-HFO were 58.96mg/g and 61.80 mg/g,respectively;H₂PO₄^-and SiO₃^2-could inhibit the adsorption performance of As???;From the point of view of stability of absorption performance and material structure,four kinds of adsorbents had a good recyclability,and adsorbents prepared by homogeneous-precursor method were more stability in material structure than adsorbents prepared by subject-object encapsulation,less material quality loss in adsorption-desorption recycling process.?3?Column adsorption experiments suggested that adsorption performance of FD@CS/HFO and FD@CS-HFO for simulated As???-containing groundwater were significantly increased than OD@CS/HFO and OD@CS-HFO,the treatment volume?BV?of FD@CS-HFO was 25 times as many as FD@CS/HFO.?4?Adsorption mechanism studies have indicated that the As???adsorption were monolayer chemical adsorption process: adsorbents prepared by subject-object encapsulation method is only bidentate complexes between the Fe-OH of HFO and As-OH of As???,and partial oxidation of As???take place on the surface of HFO;The monodentate and bidentate complexes coexisted on Fe-OH of adsorbents prepared by homogeneous-precursor method and As-OH of As???,and there was no oxidation process of As???.