| As human social development is getting more and more prosperous,social industrialization is stepping to a higher level,large amounts of pollutants have been emitted in the environment through human activities and production,of which heavy metals are relatively serious.After heavy metals enter the environment,heavy metals are difficult to remove through the self-cleaning effect of the environment,nor can they be biodegraded,and because of their biological toxicity,the adverse effects of heavy metals on human health are generally through contact and food chain.Therefore,it is of great practical significance to adopt effective methods to reduce the hazard or migration of heavy metals.The source of fly ash is mainly the accumulation of fly ash produced by the combustion of coal.After modification,it will have a larger specific surface area and rich micro-pore structure,which has a large adsorption potential for heavy metal ions.In this study,the Pb,Cu,and Cd in single and ternary systems were adsorbed by power plant fly ash modified with Na OH.The physical and chemical properties and structure of new modified fly ash（MFA）were analyzed by scanning electron microscopy（SEM）,energy dispersion X-ray spectroscopy（EDS）,specific surface area（BET）and Fourier infrared spectroscopy（FT-IR）;the adsorption experiment determined the optimum adsorption conditions of Pb,Cu,and Cd on MFA;isotherm and kinetic models were used to explain the adsorption behavior of heavy metals in MFA and combined characterization to further discuss the adsorption mechanism.By comparing the results of various characterizations,such as the changes of elements,surface microstructure and surface functional group before and after modification,it can be seen that the smooth spherical structure of the Coal fly ash（FA）was destroyed to a rough porous surface through Na OH-modification.The specific surface area increased from 1.78m2/g to 32.48 m2/g,and the functional groups on the FA such as Si-O-Si（Al）,and TO4 were destroyed to generate more active sites.The result of single adsorption of MFA in water showed that when the dosage was 2 g/L,the p H=5,the initial concentrations were Pb（200 mg/L）,Cu and Cd（100 mg/L）,and the adsorption time is Pb（30 min）,Cu and Cd（120 min）,it was the best adsorption condition.When the adsorption reached equilibrium,the adsorption amount on MFA was Pb（49.91mg/g）,Cu（40.88 mg/g）,Cd（38.78 mg/g）respectively.Compared with the one-component adsorption system,under the same adsorption conditions,the equilibrium adsorption capacity of Pb,Cu,and Cd in the ternary system reduced to Pb（48.86 mg/g）,Cu（35.19 mg/g）,and Cd（29.57 mg/g）,which indicated that Pb was adsorbed preferentially on MFA,followed by Cu and Cd,and the selective adsorption order of competitive adsorption was Pb>Cu>Cd.The adsorption of Pb,Cu,Cd in both single and competitive adsorption systems conformed to the Langmuir isotherm model,which means that the adsorption of Pb,Cu,Cd on MFA is a single-layer chemical adsorption;The kinetic analysis showed that the adsorption process under the one-element and ternary systems conformed to the pseudo-second-order model,the adsorption of heavy metal ions on MFA is dominated by ion exchange.In addition,passivation remediation of soil heavy metals was performed by MFA with organic fertilizer（JF）as an auxiliary additive material.The single and mixed use of MFA and JF were used to study the effects of different application methods on the passivation ability of heavy metals in soil and on the soil quality recovery.The soil p H,organic matter,available-nitrogen,phosphorus,potassium,Mehlich-3（M3）extractable Pb,Cu,Cd,and soil enzyme activity were determined and the correlation between various parameters was analyzed.The results are as follows:In the soil remediated by MFA and JF,the passivation ability of JF was weaker than that of MFA.The prolongation of the repair time and the increased amount of passivation agent would positively promote the remediation effect.When the addition amounts of MFA were4%,after 120-day passivation,the content of M3 extractable Pb,Cu,and Cd was reduced by62.7%,47.6%,and 48.1%,respectively.The addition of 0.6%JF could reduce the M3extractable Pb,Cu,and Cd by 32.8%,12.9%,and 22.8%,respectively.While reducing the content of JF and MFA,the JM3 treatment in the combined treatment is better than JF3 and MFA3 in effect.After the passivation,the M3 extractable contents of Pb,Cu,and Cd could be reduced by 67.8%,49.0%,and 53.5%,respectively.The analysis of soil organic matter and nitrogen,phosphorus and potassium showed that the supplementary addition of JF could make up for the lack of soil nutrients in MFA.In terms of p H,the addition of MFA increased the soil p H.Compared with CK,MFA1,MFA2,and MFA3 could increase the soil p H by 0.31,0.33and 0.39 units after the remediation for 120 days;while under the MFA treatment with JF addition of JM1,JM2,JM3,the p H at the end of the experiment was 0.04,0.14,and 0.19 units higher than CK respectively,demonstrated that the addition of JF could buffer the alkaline release caused by MFA.In terms of enzyme activity improvement,the use of MFA alone caused urease to produce stress and decreased its activity at early stage.However,as the passivation time increased,the content of heavy metals decreased,and the stress on enzyme activity also reduced.Urease activity in MFA1,MFA2,MFA3 treatments increased by 1.26,1.71 and 1.87 times,respectively.JF1,JF2,and JF3 treatments increased the activity of urease by 1.33,1.79 and 2.03 times after remediation.The JM treatment increased the activity of URE by 1.94,2.27 and 2.21 times,respectively,and the increase of ALP activity was similar to that of URE.The ALP activity in the soil treated by JM3 for 120 days increased to 28.78?g?phenol?g-1（soil）?24h-1,which was higher than the ALP activity of single MFA3 treatment.Correlation analysis among the measurement items showed that p H and CEC were significantly negatively correlated with M3 extractable heavy metals,and heavy metals were significantly negatively correlated with enzyme activity. |
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