Transformation Of Heavy Metals And Utilization Of Biochar Produced By Microwave Pyrolysis Simulated Sludge

The heavy metals contained in sludge have limited the resource utilization of sludge and its pyrolysis products.How to handle heavy metals in sludge scientifically and properly has become one of the important research contents today.Microwave pyrolysis sludge technology has gradually attracted people’s attention due to its advantages of fast and uniform heating,strong penetrating ability,low heat loss,and good heavy metal immobilization effect.However,the content of heavy metals in solid products(biochars)produced by microwave pyrolysis differs significantly and is affected by the microwave power and the final pyrolysis temperature,and to a large extent affects the future utilization resources of sludge.However,at present,few studies have been reported that the effects of sludge’s own characteristics(including a certain concentration of heavy metals)on the immobilization of heavy metals.Therefore,this study explored the influences of sludge’s own characteristics on the distribution,transformation and stabilization of heavy metals in simulated sludge by adjusting microwave power and doping with different heavy metal concentrations(Pb,Zn,Ni).And based on this,the utilization way of biochar derived from sludge pyrolysis was investigated.The effects on the distribution and morphological transformation of heavy metals in biochar by microwave power and doping of different concentrations of heavy metals were studied.The results showed that:(1)When Pb and Ni were doped,the contents of Cr,Cu,and Ni increased with increasing microwave power,whose content increased by 45.30%,66.67% and 106.88% at 1200 W,respectively,and the contents of Pb and Zn decreased.When doping with Zn,the contents of Pb decreased with the increase of power which reduced 43.89% evenly and microwave had different effects on the contents of Cr,Cu,and Ni when Zn was at different concentrations.(2)Doping with Pb had a greater influence on the content of Zn in biochar with the reduction rate of 29.55%.Doping with Zn and Ni led to the decreased of Cr,Cu,and Ni in biochar.(3)The microwave heating was more likely to transform the heavy metals from an unstable state into a stable state;the doping with Pb improved the unstable state of Zn,and the doping of Zn increased the unstable states of Cr and Ni.When doping with Ni,Pb,Cr and Ni were mainly in a stable state.(4)FE-SEM,pore characteristics and XRD results indicated that the specific surface area of biochar increased by microwave pyrolysis of sludge which could reach maximum 142.46 m2/g at 1200 W,the pore structure was advanced,and the crystal structure was the important feature for solidification of heavy metals.The effects on the stabilization(leaching characteristics)of heavy metals in biochar by microwave power and doping of different concentrations of heavy metals and the reutilization of sludge were researched.The results showed that:(1)The leaching concentration of heavy metals under microwave irradiation was much lower than that of the original sludge;(2)The doping of Pb promoted the leaching of other heavy metal;when Zn was doped,the leaching ability of heavy metals Pb,Cu and Ni also increased.With the increase of the concentration of doped Zn,the leaching capacity of Cr gradually decreased which could be reduced by 67.07%,and there was a competition between Pb and Zn;the doping of Ni promoted the leaching of heavy metals Pb and Zn,and the leaching concentration of Cr and Cu gradually decreased.(3)The optimum process parameters of the carbon adsorbent prepared by microwave method were as follows: microwave power was 1200 W,microwave irradiation time was 7 min,and potassium hydroxide activator concentration was 30 wt%.SEM and BET showed that the carbon pore structure of the sludge was well developed and the pore size was mainly mesopores.FTIR showed that the surface of the sludge carbon adsorbent had-OH,C=O,C-O,Si-O-C,Si-O-Si functional groups.The experimental results of sludge carbon adsorbing dye wastewater indicated that the adsorption effect was better when the sludge carbon adsorbent dosage was 1.4 g,the adsorption time was 120 min,the initial concentration of methylene blue was 50 mg·L-1,and the initial p H value of the solution was 4~6.