| Humic Acid(HA) existing in water and Humics from wastewater treatment plant couldcause some unpleasant color and taste and complex with heavy metals and hydrophobicorganic compounds, and then result in increasing concentration in water. As a precursor oftrichloromethane, they can also react with the chlorine disinfectants, and generatecarcinogenic chlorine compounds, which seriously influence the safety of water includingdrinking water and recycling water. Therefore, how to use the simple and reliable methods toremove humic acid is an important issue in water treatment.In this paper, we studied the HA adsorption thermodynamics on activated carbon, HAadsorption mechanism when metal ions exists in system, and HA degradation usingelectro-Fenton method with a composited of activated carbon fiber(ACF)/Fe2O3. Adsorptionkinetic parameters of HA on the carbon material surface was determined. The detailedcontents are follows:(1) Through testing the isothermal adsorption equilibrium of humic acid on activated carbon,the experimental result showed that in the whole range of HA concentration studied, theexperiment datas fit to Langmuir model; When simulating the experiment data in thesegmented HA concentration, it showed that in the low HA concentration range, thesimulation result was more suitable for Freundlich model, whereas in the high HAconcentration range, the simulation results accorded with Langmuir model; On the basisof the experimental results, we proposed two kinds of sites for humic acid adsorption onthe surface of the activated carbon. Site A, the small amount place of high activity, wasadsorbed when HA is in low concentration range; However, another kind of site B whohas low activity, only in high load does the HA combine on it.(2) The adsorption of activated carbon for HA and metal ions, Pb2+and Cd2+, when theycoexist in solution was studied, and the interaction mechanism of the ternery system wasalso investigated. The results showed that presence of HA increased metal ions adsorption,and metal ions also enhanced HA adsorption, and the mutual enhancement was influencedby solution pH. The complexation of metal ions with oxygen atoms of carboxyl orhydroxyl groups both carbon surface and HA molecular, as the main factor to influencethis promotive adsorption. Stronger complexation would cause stronger promotiveadsorption.(3) A Fe2O3/ACF composite cathode was prepared to degrade HA in Electro-Fenton system.Comperred with ACF cathode, Fe2O3/ACF cathode can increase HA removal rate tonearly20%percent. Under the optimum electrolytic conditions, the degradation rate of HA could reach to88.9%. The mechanism of this E-Fenton process was proposed to theheterogeneous Fenton reaction at the surface of Fe2O3/ACF cathode, in which H2O2wasgenerated by electro-reduction of the dissolved oxygen, and Fe2+was produced by Fe3+reduction.(4) By using zero current potential method, HA adsorption kinetics on the exterior surface ofcarbon materials was investigated, and the first and pseudo-second order kinetic equationexpressed in zero current potential were also deduced. The experiment results showed thatHA adsorption on the surface of carbon materials accorded with the pseudo-second orderkinetic equation. The apparent adsorption rate constant is1~2orders of magnitude higherthan that in HA adsorption on the porous activated carbon, which indicated HA adsorptionon the exterior surface of carbon materials was significantly faster than that on porousmaterials. This finding provides theorical basis for the development of the novel activatedcarbon materials that have super small pratical size and large exterior surface. |
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