Preparation And Characterization Of Fe-Ti Composite Oxides And Their Arsenate Adsorption Properties In Aqueous

Groundwater arsenic contamination has received extensive attention by manycountries, especially developing countries. Arsenic is serious damage to the humanphysiological system function, poisoning our human beings from skin lesions to the brain,lung, kidney, stomach cancers. After the WHO, EU and USA, China also transformed tothe new standard, to decrease the maximum limited value of arsenic in portable water to10μg/L. The new standard is put forward to further promote the deepening of the drinkingwater arsenic removal technology research. As underground water, the concentration ofarsenic is relatively low, and the properties of underground water like suspended solid andturbidity are relatively stable, adsorption is the most economical and effective way toremove arsenic. As we all know, adsorbents play the most important role in adsorption, solarge numbers of research have been promoted to develop novel effective materials. In thisresearch, compositing the advantages of iron and titanium oxides to synthesized novelFe-Ti composite bi-oxides which are effective, cheap and separated easily, to work asdrinking water adsorbent for arsenic removal.1. In this paper, iron(Ⅲ, Ⅱ)-titanium(Ⅳ) composite oxides with amorphousnanostructure named nano-FFT was synthesized, which was characterized by the X-raydiffraction (XRD) pattern, Brunauer-Emmett-Teller (BET) surface area analysis andTransmission electron microscope (TEM) imagine analyses. The characteristic resultsindicated that the nano-FFT had amorphous structure and uniform distribution of particleswith BET surface area of325.3m2/g and BJH average aperture of2.46nm (4V/A). Ingeneral, the kinetic sorption data in different temperatures and co-ions for As(Ⅴ) bynano-FFT described the pseudo-second order equation and indicated that nano-FFT hadeffective removal ability for As(Ⅴ). Meanwhile, the pore diffusion coefficient DP valueswere in the range of10-11～10-13cm2·s-1,which proved that pore diffusion was therate-limiting step. Thermodynamic parameters indicated that sorption reactions onnano-FFT were spontaneous and endothermic. The adsorption process was well consonantwith Langmuir, Freundlich and Dubinin-Radushkevich isotherms models, and thecalculated Langmuir maximum adsorption capacity in low-concentration of As(Ⅴ) couldreach26.46mg/g. Furthermore, the effect of common co-ions in ground water acting on theadsorption was investigated and Ca2+and Mg2+expressed promotion function while H2PO4-and HCO3-showed distinct inhibitory action.2. A Fe-Ti hybrid oxide adsorbent with highsorption capacities for As(V)wassuccessfully prepared using co-precipitation methods. The normal co-precipitationandreverse co-precipitation methods were introduced to optimize the properties of theadsorbents. Results of Brunauer-Emmett-Teller (BET) surface area analysis revealed thatthe specific surface area of the material is279.1m2/g and the nanoparticles adsorbent sizecalculated by BJH adsorption average pore diameter (4V/A) is7.14nm. Results ofTransmission electron microscope (TEM) showed the adsorbent agglomerated, and theX-ray diffraction (XRD) indicated that the phase of absorbent was crystalline. Throughcomparing these materials prepared by two methods in terms of following properties likeappearance, magnetism and adsorption property of arsenate, the results indicate thatmaterials which have the same proportions of iron and titanium show similar properties.With the percentage of iron reducing, the color of materials vary from charcoal grey tomilk white, meanwhile the magnetism also drops, especially when iron percentagebellowed50%, the magnetism lost basically. Adsorbents synthesized by normalco-precipitation with the proportion9:1of iron to titanium show the best magnetism andoptimum adsorption property of arsenate. When the initial concentration of arsenate was500μg/L and the absorbents were0.1g/L and0.2g/L, the removal rates of arsenate are88.3%and92.3%, the equilibrium adsorption capacity achieved4.41mg/g and2.25mg/g,respectively. The granules of adsorbent could be efficiently removed from water byenhanced magnetic field. The removal rates of turbidity of the adsorbents forfree-sedimentation and magnetic-field-sedimentation are19.4%and74.4%in initial20minutes, respectively. Apparently magnetic-field-sedimentation can separate absorbentsfrom solutions much more efficiently than traditional free-sedimentation, and the turbiditycould drop to only3NTU in three hours, which can basically satisfy the standard ofdrinking water.Above two ways of Fe-Ti bi-oxides preparation are operated simply and raw materialsachieved easily, and synthesized materials have excellent adsorption properties, especiallyunder low arsenic concentration, there showed relatively high adsorption capacity. Afteradsorption, these adsorbents can be separated rapidly by gravity or by magnetism field, so these materials can work as pota ble water adsorptions for arsenic.