| Iron minerals (FeOOH), as nonmetal mineral materials commonly found in soil and aquatic environment, include many phases of schwertmanite, goethite, akaganeite, lepdocrocite. Iron minerals can availably remove the heavy metals and rich nutrition elements from environments by the approaches of coprecipitation, irons exchange and adsorption action. At present, the most common pollution of heavy metals is arsenic, chromium pollution and so on. The trivalent arsenic, trivalent chromium and hexavalent chromium are commonly existed in mining operation, metal plating, electronic device manufacturing units and leather tanning. It will cause the pollution of surface water and groundwater, after these wastewaters discharged without treatment. Trivalent arsenic and hexavalent chromium are most toxic and carcinogenic to organism, and make great harm to human health. Eutrophication is caused by excessive nitrogen, phosphate and other nutrients. It is important to control the content of phosphate in fresh water. In recent years, many researchers pay more attention to removing heavy metals and nutrient elements by biological and nonmetal mineral. Iron minerals (FeOOH) have stable physical and chemical properties, larger specific surface areas, fine particle structures and so on, so they have beent increasingly attentted and selected as the better adsorption materials in treatment of the contaminated environments.Phases transform and environmental function of minerals are tightly related to morphology structures, interface properties and the conditions and methods of thier synthesis, so it is necessary that their structural interface properties are characterize for iron minerals to provide theoretical proofs of the function mechanism being in the both iron minerals and contaminants. The different crystal iron minerals are usually prepared by various methods, and little information is available on the relation of the characteristics of iron minerals with their synthesis method.Therefore, the objectives of the paper systematically investigate removal efficiencies for two groups of iron minerals (a group of minerals synthized by chemical methods are isomeric FeOOH including goethite Gthl/Gth2, akaganeite Akal/Aka2, lepdocrocite Lep, and the other group of chemical and biological minerals with crystalline porous structures with anion of SO4 or Cl, include schwertmannite Sch-chem/Sch-Bio and akaganeite Aka-Chem/Aka-Bio) adsobing heavy metals of trivalent arsenic, trivalent chromium, hexavalent chromium or rich nutrition elements of phosphorus. At the same time, the initially analyzed iron minerals with various particle size and the resulting material products adsorbing the pollutate are also characterized by spetral methods to examine their initial phases and structural adsorption properties of iron minerals. These results of works can explore and explain the adsoption efficiency and action mechanism on removal of the pollutates as As(Ⅲ), Cr(Ⅵ), Cr(Ⅲ) and P by various crystalline iron minerals, which is a science gist for investigation and extended application of environmental materials. The major results of all works are presented as following:Isomeric FeOOH, and schwertmannite/akaganeite with crystalline porous structure identified by XRD and FTIR are powders. The single diameter particle of iron minerals are nanostructures observed using field emission scanning electron microscopy (FESEM). For chemically and biologically synthetic schwertmannite with porous structure, there is obviously litte difference in their crystalline forms, but particle morphology structures of schwertmannite are markedly different. Diameter distribution of the suspended iron mineral particles proves that single small diameter particle of the iron precipitate products are easily assembled into the aggregated particles.The kinetics model of Lagergren second order rate equation adapted to variou crystal phase iron oxyhydroxides in two groups of minerals for adsoption of As(Ⅲ), Cr(Ⅵ) or Cr(Ⅲ) in aqueous solution with pH7. The isothermal saturated adsorption amount (mg/g) for isomeric FeOOH are shown as following,As(Ⅲ):12.6 (Gth1),7.73 (Gth2),6.40 (Akal),24.5 (Aka2),18.2 (Lep);Cr(Ⅵ):15.1 (Gth1),12.7 (Gth2),14.6 (Akal),30.3 (Aka2),13.6 (Lep);Cr(Ⅲ):11.1 (Gth1),3.18 (Gth2),14.7(Akal),11.7 (Aka2),18.7 (Lep). The isothermal saturated adsorption amount (mg/g) for schwertmannite/akaganeite with porous structure are are shown as following,As(Ⅲ):102 (Sch-Chem),110 (Sch-Bio),6.40 (Aka-Chem),30.3 (Aka--Bio);Cr(Ⅵ):119 (Sch-Chem),133 (Sch-Bio),14.6(Aka-Chem),83.6 (Aka-Bio);Cr(Ⅲ):17.3(Sch-Chem),38.3(Sch-Bio),14.7 (Aka-Chem),13.1 (Aka-Bio).The optimum pH values for removal of As(Ⅲ), Cr(Ⅵ) or Cr(Ⅲ) range in 3-8. The anions such as Cl-、NO3- and CO32- hardly had effect on heavy metal removal, while the other anion of SO42- had the greater impact on heavy metal removal and H2PO4- had greatest impact on heavy metal removal.For isomeric FeOOH in aqueous solution with pH7, the kinetics model of Lagergren second order rate equation adapted to the materials for P adsoption, and the isothermal saturated adsorption amount (mg/g) orderly are 8.86 (Gthl),8.10 (Gth2),4.66 (Akal),33.4 (Aka2),8.84 (Lep). For schwertmannite/akaganeite with porous structure in aqueous solution with pH7, the kinetics model of Lagergren second order rate equation adapted to the materials for P adsoption, and the isothermal saturated adsorption amount (mg/g) orderly are 227 (Sch-Chem),323 (Sch-Bio),4.66 (Aka-Chem),68.5 (Aka-Bio). The optimum pH values for P removal range in 3-8. The anions such as Cl-、NO3- and CO32- hardly had effect on P removal, while the other anions of SO42- had the greater impact on P removal and H2PO4- had greatest impact on P removal.After the asorption of As(Ⅲ), Cr(Ⅵ), Cr(Ⅲ) and P by isomeric FeOOH and schwertmannite/akaganeite with porous structure, the infrared peak of mineral sorbents with porous structure become weak and disappeared, even some new peak appeared, compared with those of initial iron minerals. |
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