| Heavy metal wastewater is one kind of the industrial wastewater,which is the serious hazard to environment and human health. So far,lots of methods have been used to treat heavy metal wastewater,including adsorption by active carbon. In this experiment, granularactivated carbon （GAC） was modified with HNO3solution （10%and30%, v/v） by standing oxidation/reflux condensation, in order toimprove the adsorption capacity.Surface physicochemical properties of pre-modified andpost-modified activated carbon were studied through specific surfacearea test, Boehm functional group titration, scanning electronmicroscope （SEM） inspection, FT-IR analysis, etc. The results showdthat the specific surface areas of10%N-GAC and30%N-GAC weredetected as762.29m2/g and771.55m2/g, respectively, which wereseparately decreased by2.62%and3.78%in comparison with that ofGAC. The average pore size and total pore volume of the modified GACwere also significantly reduced. Whereas the contents of acidicoxygen-containing groups after the modification increased and thecorresponding acidic groups of10%N-GAC and30%N-GAC were0.72mmol/g,0.483mmol/g and0.54mmol/g, in respect, which were2.32 and1.74times higher than that of GAC.The influence of adsorption time, dosage, pH, and initialconcentration on Cu（Ⅱ） and Cr（Ⅵ） adsorption by the pre-modified andpost-modified activated carbon was studied in this experiment. It wasfound that, adsorption equilibrium time of Cu（Ⅱ） and Cr（Ⅵ）bymodified GAC were3hours and5hours, respectively. When the initialconcentration of Cu（Ⅱ） solution was10mg/L, optimal dosages of the30%N-GAC were3g/L but5g/L of GAC and10%N-GAC.Cu（Ⅱ）removal efficiency of30%N-GAC with3g/L dosage was1.56and2.06times higher than those by10%N-GAC and original GAC. When theinitial concentration of Cr（Ⅵ） solution was10mg/L, optimal dosages of30%N-GAC,10%N-GAC and original GAC were4g/L,10g/L and12g/L, respectively, Cr（Ⅵ） adsorption efficiency of30%N-GAC with4g/L dosage was1.70and1.96times higher than those by10%N-GACand original GAC. Within pH range of4-10, an elevation in pH valuewould be beneficial to adsorb Cu（Ⅱ）, but not conducive to adsorbCr（Ⅵ）.The adsorption of Cr（Ⅵ） and Cu（Ⅱ） increased with the increaseof initial metal concentration until equilibration, then the removal ratestarted to decrease.According to the adsorption results of Cu（Ⅱ） and Cr（Ⅵ）, themechanism of heavy metal adsorption was studied. The adsorptionisotherm using two adsorbents （30%N-GAC and GAC） all conformed to Langmuir adsorption equation, which suggested that Cu（Ⅱ） and Cr（Ⅵ）adsorption by these two methods belonged to single molecule layerabsorption. The data of Cr（Ⅵ） absorption by the three adsorbents werewell fitted into Lagergren pseudo-secondary rate equation. The dynamicprocess of Cu（Ⅱ） adsorption by30%N-GAC conformed to Lagergrenpseudo-secondary rate equation; while the processes by10%N-GAC andoriginal GAC conformed to Lagergren pseudo-first rate equation in theearly90minutes, after that they conformed to Lagergrenpseudo-secondary rate equation. And all the correlation coefficientswere above0.99. |
