Research On Iron-Carbon Material For The Removal Of Typical Heavy Metal Complexes And Oxacid Root Pollutants In Wastewater

Abstract:Large amount of heavy metals and oxacid root pollutants were discharged into the environment, which may results in serious environmental pollution and human health risk. Heavy metals and oxacid root contaminated wastewater with the characteristics of bioaccumulation, high residue and semi-volatile were focused by wastewater researcher. In this study, the typical heavy metal complexes Cu-EDTA and dichromate oxacid root were chosen as the object. Two novel methods were developed for synthesis of iron carbon materials Fe3O4/CNTs and Fe/AC, and the new materials were explorerd for removal of Cu-EDTA and dichromate from aqueous solution effectively. The main research contents and creative achievements are as follows:Based on the characteristics of the pulse plating, a novel flip plating iron-carbon material production device was designed, which was used to load zero-valent iron on the carbon surface. Optimum conditions to prepare the iron-carbon materials were investigated, plating time is30min, current intensity is2.5A, ion concentration of electrolyte is150mg/L. Under the above conditions, the Fe/AC materials prepared was rich in hydroxyl group, carboxyl group, carbon-oxygen double bond, and zero-valent iron-carbon complex structure on its surface, which enable the iron-carbon material Fe/AC conducive to the removal of the Cu-EDTA pollutants.A novel method for synthesis of high ferromagnetism nanoparticles (Fe3O4/CNTs) were proposed to efficiently remove Cr(VI) from aqueous solution. The Fe3O4/CNTs were prepared via an in-situ reduction with post-oxidation (RPO) method by using cheap and environmental friendly precursor under the mild condition. Magnetic hysteresis loops revealed that Fe3O4/CNTs had superior saturation magnetization (152emu/g) enabling the high-efficient recovery of Fe3O4/CNTs from aqueous solution by magnetic separation at low magnetic field gradients. The hydroxyl and carboxyl groups generated during preparation process can conjunct effectively with heavy metals in wastewater. Fe3O4/CNTs is an effective and environmental friendly adsorbent to remove heavy metals from wastewater attribute to the efficient removal ability and separation property.Batch experiments were performed to explore the optimium conditions of Cu-EDTA wastewater treatment by Fe/AC material. The removal efficiency is optimal at pH value of4.0, temperature of298K. Under the above conditions, the residual concentration of Cu(?) decreased from60mg/L to1.718mg/L. Based on the Cu-EDTA treatment results, the reasonable organic compounds degradation mechanism were proposed firstly. The mechanism identified the relationship between organic heavy metal complexes destruction and hydroxyl radicals. Futhermore, the necessary hydroxyl radical generating conditions were authenticated by electrochemical theory, which is pH<7, dissolved oxygen, and electron transfer on Fe/AC surface. The hydroxyl radical generating chemical equation was derived. The concentration of hydroxyl radical can be calculated by equation of lg[·OH]=36.69-lg[Fe3+]+lgPo-3pH and the Gibbs free energy of the equation is-64.73KJ/mol, which reasonably revealed the degradation mechanism of heavy metal-organic complexes.Cr(VI) ionic forms in wastewater were analyzed. The effect of Fe3O4/CNTs on dichromate containing wastewater was investgated via batch experiments. Visual MINTEQ3.0modeling program was adopt to determine aqueous speciation of chromium ions at different pH values. Illustrated that the different forms of chromium ions such as Cr2O72-, KCr2O7-and HCrO4-coexist with predominant KCr2O7-in the pH range of1.0-6.0, these forms transformed to CrO42-and KCrO4-with pH increasing.The optimal conditions of Cr(VI) treatment experiments is as follows:pH value is6, temperature is313K and contact time is30min, Under the above conditions, the maximum Fe3O4/CNTs adsorption capacity reached to57.49mg/g, which is higher than the common adsorbents Kinetics, thermodynamics and the Cr(VI) removal mechanism indicated that Cr(VI) adsorption process in accordance with Langmuir model, D-R model and pseudo-second-order kinetic model. Thereinto, the adsorption energy is11.61KJ/mol, Langmuir constants are0.103-0.386. which revealed Cr(VI) adsorption process on Fe3O4/CNTs is monolayer adsorption, ion-exchange adsorption, and chemical adsorption process is rate determining step. Futhermore, Raman analytical results clarified the magnetic of Fe3O4/CNTs were all generated by Fe3O4, and the final state of Cr(VI) adsorpt on the Fe3O4/CNTs are Cr(OH)3and Cr2O3crystal structure. The change of surface properties of Fe3O4/CNTs provided the reliable evidence for the adsorption mechanism.According to the on surface groups and metal valence analysis, stable configurations and orbital energies of Fe/AC and Fe3O4/CNTs were calculated. The steady relationship between pollutants and various group on Fe/AC and Fe3O4/CNTs surface was deduced. Dmol3module of Materials Studio5.5program was used to construct the stable structures of complexes formed between a variety of functional groups present and the different heavy metal ions. Moreover, In order to guide the modification of AC and CNTs the energies of the frontier molecular orbital for the complexes were calculated. This research reveals the highest stabilization energy is carboxyl and dichromate complexes, and followed by hydroxyl and dichromate groups, carbon-oxygen double and dichromate bond is the weakest. Fe/AC and Fe3O4/CNTs developed in this study have great potential for the advanced treatment of wastewater containing heavy metal complexs and heavy metal oxacid roots. Figures86, Tables22, References209.