Effects Of Modified Corn Straw Biochar On Properties And Speciation Distribution Of Heavy Metals Cadmium And Lead In Black Soil And Peat Soil

Since the middle and late 20th century,with the rapid development of industry and agriculture,the situation of soil heavy metal pollution in China is severe.The pollution of heavy metals in soils is difficult to control because of its long-term,concealment and universality,and can seriously endanger human health through the role of food chain.That looking for cheap and effective methods to control soil heavy metal pollution has become a research hotspot.Biochar is often used as soil remediation agent and soil conditioner because of its low cost,wide source and excellent structural characteristics.Generally,the original biochar cannot meet the actual needs of soil remediation and soil improvement due to the lower actual use effect..For different soils polluted with heavy metals,different methods can be used to modify biochar to achieve the purpose of more effective remediation of soil heavy metal pollution.Therefore,the study of the effects of modified biochar on soil physi-chemical properties and the distribution of heavy metals will be of great significance for the effective use of corn straw biochar to improve soil and repair soil heavy metal pollution.In this paper,corn straw was used as biochar raw material to prepare biochar at different temperatures of 300 ℃,500 ℃ and 700 ℃,respectively(expressed with BC300,BC500 and BC700 at different temperatures,respectively),and corn straw biochar(BC500)was modified with acid and alkali(expressed with HBC500 and KBC500,respectively).The structural characteristics of different corn straw biochar were analyzed by scanning electron microscope and Fourier infrared spectroscopy.The effects of different kinds of corn straw biochar(BC300,BC500,BC700,HBC500 and KBC500)added in black and peat soils with different amounts(0.5%,1.0% and 3.0%)on the properties of soils and the form distribution of Cd and Pb were studied by indoor simulation experiment in black soil and peat soil.(1)The results from the characterization of corn straw biochar(BC300,BC500 and BC700)showed that the specific surface area,micropore and porosity of corn straw biochar increased with the increase of pyrolysis temperature,however the collapse of the surface of biochar occurred at high temperature,which resulted in the destruction of morphological structure.The surface functional groups of biochar increased with the increase of temperature within a certain temperature.The morphological structure characteristics of corn straw biochar(BC500)prepared at 500℃ was the optimal.The surface of acid modified corn straw biochar(HBC500)was damaged,the pore size increased,the pore structure was irregular,and the specific surface area decreases.The pore structure of alkali modified corn straw biochar(KBC500)was clear and obvious,both the pore size and the specific surface area increased compared with biochar HBC500 and BC500.(2)The results from the effects of corn straw biochar BC300,BC500 and BC700 on the properties of black soil and peat soil and the distribution of heavy metals showed that the addition of 3% BC500 increased the p H and the content of black soil,the soil p H increased to 6.80 ± 0.12,the content of organic matter increased to 4.96% ± 0.29.The residual content of Cd and Pb in black soil increased 13.81% ± 2.61% and 1.18%± 5.79%,respectively.Meanwhile,the addition of 3% BC500 increased the p H and the content of organic matter of peat soil,soil p H increased to 6.26 ± 0.11 and the content of organic matter increased to 30.39% ± 3.06%,and the residual content of Cd and Pb in peat soil increased 10.96% ± 1.29% and 74.49% ± 6.67%,respectively.BC300,BC500 and BC700 increased the p H and organic matter content of black soil and peat soil,and reduced the activity of heavy metals Cd and Pb in black soil and peat soil to varying degrees,especially,BC500 had the most significant effect on the increase of p H and organic matter content of black soil and peat soil and the decrease of active content of heavy metals Cd and Pb in black soil and peat soil.(3)The results effects of modified biochar(HBC500 and KBC500)on the properties of black soil and peat soil and the form distribution of heavy metals showed that KBC500 with 3% addition could increase the p H of black soil to 6.97 ± 0.05 and the content of organic matter to 4.98 ± 0.26%.Compared with that of 3% BC500,3%KBC500 increased the residual contents of Cd and Pb in black soil by 11.69% ±1.61% and 14.76% ± 2.67%,respectively;KBC500 with 3% addition increased the p H of peat soil to 6.06 ± 0.08% and organic matter to 30.49% ± 1.06%.The residual contents of Cd and Pb in peat soil increased by 17.75% ± 5.37% and 5.39% ± 2.93%,respectively,compared with that of BC500 with 3% addition.The addition of KBC500 increased the p H and organic matter content of black soil and peat soil more significantly,and increased the residual Cd and Pb content in black soil and peat soil more significantly,which was positively correlated with the addition of KBC500,compared with that of BC500.The addition of HBC500 could significantly increase the organic matter content of black soil and peat soil,the maximum organic matter content reached to 4.81% ± 0.26% and 28.98% ± 1.71% respectively,significantly reduced the p H of black soil and peat soil,the minimum p H value decreased to 5.24 ± 0.06 and 4.61± 0.07 respectively,as well as,increased the content of Cd and Pb in the active forms(water-soluble,acid extractable and reducible)of black soil and peat soil compared with that of the addition of BC500.It indicated that alkali modified biochar KBC500 was more conducive to the improvement of black soil and peat soil and the decrease of heavy metal Cd and Pb activities,furthermore,reduced the pollution risk of heavy metals in soils.