| With the rapid urbanization and industrialization in our country,the amount of the discharged sewage increases continuously.As a by-product,the sludge also presents a trend of rapid growth.The sludge usually contained some heavy metals,which have attracted great attentions,and the disposal for the sludge has been become an important field for waste treatment.In this project,the sludge came from the sewage treatment plant of Kaifeng County was taken as the experimental material.Based on microwave digestion using H2O2-Aqua regia-HF,the total contents of heavy metals,such as Cr,Cd,Pb,Mn,Co,Ni and Cu were determined by using inductively coupled plasma-atomic emission spectrometry?ICP-AES?,as well as the form of sludge were extracted using BCR method and the stabilities of heavy metals in environment were investigated by using leaching toxicity test.ICP-AES results showed that the content of Cd was higher than the standard,Mn was slight high with the content of 211mg·kg-1,and the contents of other metals were lower than the discharged standard of pollutants.BCR results indicated that Mn was mainly in unstable state with acid soluble in largest proportion,the contents of the stable states of Co,Ni,Cd and Pb were higher than that of the unstable states with similar form proportion,and Cu and Cr were mainly in stable states.The leaching toxicity analysis displayed the leaching toxicity of Mn is highest with potential risks,the leaching toxicity of Ni is moderate,while the leaching toxicities of other metals were low with little risk in farming.The effects of thermal treatment temperature on the migration of heavy metals were investigated.Results showed that the residual states for seven elements tended to be stable with the increased temperature.When the temperature was 700 oC,the residue states of Pb,Ni,Co,Mn and Cr reached the highest.From the results of SEM,the sintering appeared with the increased temperature.At 600 oC,the sludge started to aggregate and the particles became coherent and unclear.The larger dense occurred at 700oC,and the agglomeration state was shown at 800 oC.The leaching toxicity experimental showed that the leaching content of each heavy metal was in the same trend to that of the form distribution under different temperatures.Moreover,the leaching contents of seven heavy metals were decreased by elevated temperature.The sludge was modified using the 2-mercaptobenzothiazole?MBT?,followed by being used for the adsorption of heavy metals.FTIR results showed MBT were successfully grafted on the sludge surface.The adsorption of Copper on the modified sludge was investigated.It showed that,under certain temperature and concentration,the adsorption process could be better fitted by Freundlich adsorption isotherm model with the correlation coefficient of 0.9683.In addition,the process was found to be followed by quasi two order kinetic equation with the correlation coefficient of 0.9999 and the theoretical qe value of1.313 mg·g-1,which was close to the experimental one of 1.125 mg·g-1.The intraparticle diffusion and Elovich equation could reflect the mode at the initial adsorption stage,and the adsorption process was the interaction of intraparticle diffusion and other adsorption processes.By fitting the adsorption thermodynamics data,the adsorption enthalpy change?H0 and adsorption entropy change?S0 were found to be greater than zero,and?G0 was negative,indicating the adsorption was exothermic and spontaneous.After adsorption,the confusion degree of the whole system were reduced.The optimum conditions were investigated by using the response surface method.Results showed that the adsorbent dosage and the contents of heavy metals in sludge had notable influences,while the influence of stirring time on adsorption was not significant.The quadratic term indicated that the adsorbent dosage had observable effect,and the interaction was not notable.The optimum conditions was 2 mg·g-1 of the concentration of heavy metals in sludge,0.3 g of the adsorbent dosage,and 1 h of the stirring time. |
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