Heavy Metal And Dye Adsorption Properties Of Corn Stalks Composite Superabsorbents

With industrial development, discharge wastewater containing heavy metals anddyes into the environment has brought great pressure to environment, thereforeseeking abundant and environmentally friendly adsorbents of heavy metals and dyeshas become an important research hot spot for the future wastewater treatment ofheavy metals and dyes. Straw is a kind of natural material whose main componentsare cellulose,hemicellulose and lignin, with a large number of hydroxyl, carbonyland other reactive groups on the molecular chain. Straw might be used as a greenadsorbent for heavy metal-and dye-containing wastewater treatmentthroughappropriate modification in order to introduce some new functional groups into thestraw molecular chains.In this paper, phytic acid modified-corn stalks composite superabsorbent wassynthesized, and the effects of polymerization condition and adsorption condition onthe heavy metal ions and cationic dye adsorption propertieswerestudied.Thermodynamics and kinetics of heavy metal ions and cationic dyeadsorption of the phytic acid modified-corn stalks composite superabsorbent wereinvestigated. Morphologies and structureof the phytic acid modified-corn stalkscomposite superabsorbent were characterized by SEM, FTIR and optical microscope.Possible adsorption mechanisms of heavy metal ions and cationic dye for the phyticacid modified-corn stalks composite superabsorbent were discussed. The phytic acidmodified-corn stalks composite superabsorbent, having good heavy metals andcationic dyes adsorption properties, can be used widely to deal with environmentalpollution of heavy metals-and dyes-containing wastewater. The main researchresults are as follows:1. Factors affecting the heavy metals adsorption properties of the phytic acid modified-corn stalks composite superabsorbent, such as amount of phytic acidmodified-corn stalks, phytic acid grafting degree, initiator amount, crosslinkeramount, neutralization degree of itaconic acid, itaconic acid/acrylamide mas ratio,were investigated. The optimal polymerization condition for the phytic acidmodified-corn stalks composite superabsorbent having maximum heavy metalsadsorption properties is as follows:10%phytic acid modified-corn stalks,11.91%phytic acid grafting degree,1.6%initiator,0.4%crosslinker,65%itaconicacidneutralization, itaconic acid/acrylamide mas ratio of30:70.2. Factors affecting the cationic dyesadsorption properties of the phytic acidmodified-corn stalks composite superabsorbent, such as amount of phytic acidmodified-corn stalks, initiator amount, crosslinker amount, neutralization degree ofitaconic acid were investigated. The optimal polymerization condition for the phyticacid modified-corn stalks composite superabsorbent having maximum cationicdyesadsorption properties is as follows:10%phytic acid modified-corn stalks,1.6%initiator,0.4%crosslinker and65%itaconic acidneutralization.3.Adsorption conditions influencing heavy metals and cationic dyesadsorptionproperties of the phytic acid modified-corn stalks composite superabsorbent, such asadsorption time, pH value, heavy metals and cationic dyes initial concentration,adsorption temperature, were studied. Bothe heavy metal ions and cationic dyeadsorption capacity increased with increase of adsorption time and increase of pHvalues. Cationic dye adsorption capacities of the phytic acid modified-corn stalkscomposite superabsorbent increased with increasing temperature, and the cationicdye adsorption rate accelerated with increasing temperature. With increasing ofheavy metals and cationic dyes initial concentration, heavy metal ions and cationicdye adsorption capacitiesof the phytic acid modified-corn stalks compositesuperabsorbentincreasedmore and more slowly. When the initial concentrations ofcopper ions, methylene blue and methyl green were1400mg/L, adsorptioncapacities of the copper ions, methylene blue and methyl green reached1073mg/g,1317mg/g and890mg/g, respectively.4. Methylene blue adsorption process of the phytic acid modified-corn stalkscomposite superabsorbent accorded with Langmuir adsorption model, whereas Cu2+ion and methyl green adsorption process complied with Friedrich equation. Bothcopper ions and cationic dye adsorption processesare spontaneous and endothermicwith adsorption mainly by chemical reactions. Both copper ions and cationic dyeadsorption processes are in line with the pseudo-second kinetic model.5. FTIR spectra results showed that the synthesizedcomposite superabsorbentshave phytic acid modified corn stalks unit, NVP unit, IA unit andAM unit, indicating that the phytic acid modified-corn stalks compositesuperabsorbents with target structure have been synthesized.6. SEM images showed that the phytic acid modified-corn stalks compositesuperabsorbentshad porous surfaces with many grooves and voids, which isbeneficial for heavy metal ions and cationic dye solutionto rapidly penetrateinto theinside of superabsorbentnetworks, and thus improving heavy metal ions and cationicdye absorption properties of the phytic acid modified-corn stalks compositesuperabsorbents.