Characterization Of Phosphorus Enhanced Engineered Biochar And Its Performance On Cd And Pb Immobilization In Contaminated Soils

At present,the problem of heavy metal pollution in farmland soils in China is severe.As a heavy metal solidification material and soil improvement material,biochar has attracted much attention in the in-situ stabilization project remediation of contaminated soil.In order to further improve the in-situ stabilization efficiency of biochar materials to soil heavy metals,the contaminated soils collected from Fengxian（FX）in Shaanxi and Kunming（KM）in Yunnan was selected as the research object,and swine manure and Ca（H₂PO₄）₂were selected as raw materials in this study,and the swine manure biochar（SMB）and phosphorus enhanced swine manure biochar（PSMB）were prepared at 700℃by the high-temperature pyrolysis method.The experiment explored the stabilizing potential of SMB and PSMB for cadmium（Cd）and lead（Pb）in soil.Firstly,the pore structure,composition and physical and chemical properties of different kinds of biochars were characterized and analyzed by means of BET,SEM-EDS,FTIR,XRD and other techniques.Secondly,three acids digestion,DTPA-extraction and BCR sequence extraction were used to evaluate the solidification effect of biochar on soil heavy metals,and then soil nutrients were measured to evaluate the effect of biochar addition on soil fertility.Finally,pot experiment,the biomass of Chinese cabbage,and the contents of heavy metals in the shoots and roots of plants were carried out to evaluate the effects of biochar addition on soil fertility,plant heavy metal uptake and plant growth.The main results and conclusions are as follows:（1）After the modification,the p H of the biochar increased from 11.07 to 11.28,the EC value increased from 3920 to 4830(μS·cm^-1),the ash yield increased from 64.48%to67.92%,and the specific surface area of biochar has been reduced from 39.38 m²·g^-1to 16.77m²·g^-1.But the total pore volume hasn’t changed much(The total pore volume of SMB is0.064 cm³·g^-1and the total pore volume of PSMB is 0.060 cm³·g^-1).According to the results of SEM-EDS,the pore size of SMB is indeed larger than that of PSMB,and the phosphorus（P）content of PSMB is obviously higher than that of SMB.In addition,the pyrolysis of biomass has led to a rearrangement of functional components.As you can see from the infrared spectra（FTIR）of SMB and PSMB,the peaks of PSMB and SMB can be seen at1419 cm^-1,which is the telescopic vibration peak of C=C,and it is clear that the peak of PSMB is more obvious here.There are also peaks at～555 cm^-1and 1037 cm^-1,which is the P-O bond and the intensity of PSMB at these two peaks is significantly higher than that of SMB,which shows that there are more P-O bonds in PSMB.Large quantities of inorganic minerals can be clearly observed by XRD diffraction of biochar materials.It is clear from the XRD diffraction patterns of SMB and PSMB that PSMB has two distinct peaks from SMB at2θ=20.99°and 2θ=26.50°.Further analysis indicates that these two peaks are brushite and monetite,respectively.（2）Adding SMB and PSMB can change soil p H,increase soil EC.The addition of3%SMB and 3%PSMB could significantly increase the contents of Available-P,Available-K and soil organic matter（SOM）of FX and KM.Compared with FX and KM original soil,the addition of 3%PSMB increased the available-P in FX soil by 7.82 times,and increased the available-P in KM soil by about 8.13 times.Under the control and SMB3%treatment,the Available-K content in soils were increased from 397 mg·kg^-1and 28mg·kg^-1of the control to 1507 mg·kg^-1and 1021 mg·kg^-1of SMB 3%treatment,respectively;In addition,the increase in SOM is significantly positively correlated with the amount of SMB and PSMB applied.（3）The addition of SMB and PSMB significantly reduced the effectiveness of Cd and Pb in the FX and KM soils compared to controls.Compared to adding 1%SMB,3%SMB,and 1%PSMB to FX and KM soil,adding 3%PSMB could decrease the concentration of 34.02%DTPA-Cd and 18.70%DTPA-Pb in FX soil and 47.73%DTPA-Cd and 24.58%DTPA-Pb in KM soil.In addition,the ratio of acid-soluble Cd and Pb in FX and KM soils treated with all biochar was reduced as compared to the control,while the ratio of the residual Cd and the reducible Pb was increased significantly.（4）The addition of 3% PSMB increased the shoot biomass of FX Chinese cabbage to1.62 times of the control;The shoot biomass of KM increased to 1.27 times of the control.The application of 3%PSMB in FX soil reduced Cd and Pb by 19.23%and 46.54%in shoot of Chinese cabbage,and 38.31%and 43.10%in root of Chinese cabbage.The application of3%PSMB in KM soil reduced Cd and Pb in shoot of the Chinese cabbage by 84.66%and56.33%,and the Cd and Pb in the root by 86.89%and 54.80%,respectively.All in all,the pot experiment further confirmed that the addition of biochar contributes to the increase of biomass of Chinese cabbage.The application of 3%PSMB in FX and KM soil significantly reduced the absorption of Cd and Pb in Chinese cabbage.This study shows that the application of PSMB can not only effectively promote the stabilization of Cd and Pb in contaminated soil,but also effectively improve the level of soil fertility supply.It is a soil improvement material with a certain application prospect.