Study Of Adsorption Property And Mechanism For Dyes And Heavy Metals On Citric Acid-modified Rape Straw

In this study, a novel biosorbent is prepared that agricultural and forestry waste rapestraw is used as matrix,citric acid is selected as multi-functional small molecules to theirsurface modification.And modern analytical instruments is used to analysis itsmorphology and surface elements.The static and dynamic adsorption behavior of dye(malachite green and neutral red) and heavy metals (Pb (II) and Cd (II)) from aqueoussolution on the novel adsorbent is studied and the adsorption mechanism is discussed.Theregenerative properties of the sorbent is also investigated. The main research work andthe results are as follows:(1) Preparation and characterization of novel adsorbentIn this study, citric acid is used to modified rape straw. SEM(Scanning electronmicrograph) and XPS(X-ray Photoelectron Spectroscopy) are used to characterize thesurface morphology and elements propertied of the products. SEM characterizationresults indicate that rape straw has multiple fibrous structure which is conducive toadsorption; XPS characterization results show that active group(O-C=O) increasedsignificantly after modification which indicate that graft changes the surface elementscomposition of rape straw and citrate grafted onto the rape straw successfully..(2)Static adsorption properties and mechanisms of dyes on citric acid-modified rapestrawThe static experimental results of adsorption of citric acid-modified rape straw onneutral red and malachite green show that modified rape straw has the best removalefficiency which can reach99%and95%when the concentration of the adsorbent dosageis1.2g/L, pH is the two dyes own pH,adsorption time is180min, the initial concentrationis400mg/L, adsorption temperature is at25℃.Citric acid-modified rape straw showshigh adsorption capacity on these two dyes, and the maximum adsorption capacity forneutral red and malachite green in the experimental is387.3mg/g and390.5mg/g, respectively. Langmuir isotherm model and the pseudo-second model can simulate theadsorption processof neutral red and malachite green on rape straw well, indicating thatadsorption is monolayer adsorption and adsorption process belongs tochemicaladsorption.(3)Dynamic adsorption properties and mechanisms of dye on citric acid-modifiedrape strawThe static experimental results of adsorption of citric acid-modified rape straw onneutral red and malachite green show that citric acid-modified rape straw has goodremoval efficiency when the adsorbent dosage is0.2g, pH is the two dye original pH,flow rate is5mL/min, the initial concentration is400mg/L.The breakthrough time andadsorption column saturation time for neutral red was65min and90min,respectively.And for malachite green, breakthrough time and adsorption column saturation time was70min and95min, respectively.Thomas model show a good simulation of dynamicadsorption process rape straw on neutral red and malachite green,which indicate thatdynamic adsorption on dye is monolayer adsorption, and has no axial diffusion.(4)Static adsorption properties and mechanisms of heavy metals on citricacid-modified rape strawThe static experimental results of adsorption of citric acid-modified rape straw onPb2+and Cd2+show that modified rape straw owns high removal efficiency which theremoval ratio can reach98%and95%，respectively, when the concentration of theadsorbent dosage is1.2g/L and2g/L, the initial concentration is200mg/L and50mg/L,respectivley，pH is the two metals original pH, adsorption time is180min, adsorptiontemperature is at25℃. The experiments results show that citric acid-modified rape strawowns strong adsorption capacity on two metals, and the maximum adsorption capacityfor Pb2+and Cd2+in the experimental was164mg/g and26.6mg/g, respectively.Langmuir isotherm model and the pseudo-second model can describe the adsorptionprocess better, which indicate that adsorption is monolayer adsorption and adsorptionprocess belongs to chemical adsorption. (5) Dynamic adsorption properties and mechanisms of heavy metals on citricacid-modified rape strawThe Dynamic experimental results show that the novel adsorbent citic acid-modifiedrape straw has good removal efficiency to Pb2+and Cd2+when the adsorbent dosage is0.2g, pH is the metal solution original pH, flow rate is5mL/min, the initial concentrationis200mg/L and50mg/L, respectively.The breakthrough time and adsorption columnsaturation time for Pb2+was30min and55min, respectively, and for malachite Cd2+breakthrough time and adsorption column saturation time was30min and65min,respectively.Thomas model show a good simulation of dynamic adsorption process ofPb2+and Cd2+on rape straw,which indicate that dynamic adsorption of two heavy metalsare monolayer adsorption on citric acid-modified rape straw, and has no axial diffusion.(6)Research of regeneration performance of citric acid-modified rape strawThe regeneration results for citric acid-modified rape straw show that soaking withHydrochloric acid can make saturated adsorbent desorp and regenerate, the adsorbentafter regeneration shows the substantially same adsorption capacity as the freshadsorbent, indicating that the novel adsorbent has a good regeneration property.