Physicochemical Characterization And Behavior Of Hydrotalcite-like Compound Toward Nitrate Removal

Owing to agricultural and industrial activities, the nitrate concentration in surface andgroundwater has increased to such an extent that the admitted standards in drinking waterhave been largely exceeded in many regions of the world. WTO and US EnvironmentalProtection Agency （EPA） has set the maximum contamination level as10mg/L of NO3--N.Elevated nitrate concentrations in drinking water sources present a potential risk to publichealth. The removal options that are discussed in this paper include physical denitrification（reverse osmosis, ion exchange）, biological denitrification, and catalytic reduction. Manyconventional methods of removing nitrate from water exists some disadvantages. Amongthem the adsorption technology has the following advantages: high removal efficiency, quickreaction rate, short residence time, simple operation conditions, and low economic cost.A series of calcined hydrotalcites （CHTlcs） were made by coprecipitation method,according to its adsorption effect of nitrate, focus on the research analyzes the experimentrequired adsorbent–Mg/Fe and MgAlFe hydrotalcites. Characteristics of adsorbent materialsvia X-ray diffraction （XRD） and Fourier-transform Infrared spectra （FTIR） were examined tovalidate the adsorption efficiencies of hydrotalcite. The adsorption experiments were carriedout under various equilibration conditions, such as adsorbent dose, pH, temperature andcompetitive ions. The kinetics and isotherm patterns of adsorption were analyzed tounderstand the underlying mechanism of nitrate adsorption on hydrotalcite. To the followingconclusions:（1） A series of calcined layered double hydroxides with different chemical compositionwere investigated to remove nitrate. The highest nitrate percentage of adsorption （about96%）and adsorption capacity （about70mg/g） were obtained by using the CHTlcs with Mg/Femolar ratio of3. Considering nitrate adsorption removal, adsorption capacity, and economicenvironment or other factors, it was found that1.5g/L Mg/Fe CHTlcs could achieve idealadsorption efficiencies of nitrate during the nitrate adsorption process with an initial nitrateconcentration of100mg/L at pH8and at room temperature. Various co-existing anionsinterfered in the adsorption of nitrate. The inhibitory effect was in the order of phosphate>sulphate> chloride. Adsorption isotherms showed that the experimental equilibrium data wasfitted better by the Langmuir isotherm model than the Freundlich. And the adsorption kineticswas successfully fitted by pseudo second-order kinetics.（2） By reference to the experimental method of above layered double hydroxides. It wasfound that1.5g/L MgAlFe CHTlcs at molar ratio of3could achieve ideal adsorption efficiencies of nitrate during the nitrate adsorption process with an initial nitrate concentrationof100mg/L at pH8and at temperature30℃. The inhibitory effect of various co-existinganions was in the order of PO₄^3－> SO₄^2－>Cl^-> ClO₄^-. Adsorption isotherms showed that theexperimental equilibrium data was fitted better by the Langmuir isotherm model than theFreundlich. And the adsorption kinetics was successfully fitted by pseudo second-orderkinetics.