Passivation And Adsorption Of Biochar-based Fertilizer To Cadmium,Lead And Chlorpyrifos In Soil

In recent years,using biochar as fertilizer carrier to prepare biochar-based fertilizer for controlling soil pollution and nitrogen loss has become a new research hotspot at home and abroad.Heavy metals and pesticides are typical pollutants in farmland soils.At present,there are many studies on the adsorption of these two kinds of pollutants by biochar.However,there are few studies on the passivation of soil heavy metals and the adsorption of pesticides by biochar-based fertilizers.In this paper,we chosed cadmium?Cd?,lead?Pb?and chlorpyrifos in soils as the target pollutants.The passivation and adsorption performance of Cd,Pb and chlorpyrifos in soils by biochar-based fertilizers from rice husk and urea peroxide were studied by batch adsorption test and soil culture,based on the optimization of Response Surface Methodology?RSM?for the preparation of biochar-based fertilizers.The results provide a scientific basis for the application of biochar-based fertilizer in the control of contaminated soil in farmland.The main results are as follows:1.RSM was used to optimize the preparation of biochar-based fertilizers.The optimized conditions for the slow-release ability of nitrogen from biochar-based fertilizer were observed at 16.89%water addition under the use of 25%kaolin when the fertilizer-biochar mass rate was 0.2,which was 74.32%lower than that of the control group only using urea peroxide.Biochar loaded with urea peroxide can produce more oxygen-containing functional groups such as-OH,-C-O,-C=O,which provides the possibility of adsorbing more heavy metals.The above-ground biomass of Chinese cabbage increased by 83.58%and 87.79%compared with the control group and the biochar treatment group after the application of biochar-based fertilizer,which indicated that the biochar-based fertilizer could control nitrogen loss and promote crop growth.2.The adsorption process of biochar-based fertilizer for Cd²⁺and Pb²⁺accords with the second-order kinetic model,which indicates that the adsorption of Cd²⁺and Pb²⁺by biochar-based fertilizer is mainly chemical adsorption.Isothermal adsorption experiments showed that Langmuir isothermal adsorption model can better describe the adsorption behavior of biochar-based fertilizers for Cd²⁺and Pb²⁺than Freundlich isothermal adsorption model,indicating that the adsorption process is mainly based on a monolayer adsorption behavior.Compared with biochar,the adsorbability of biochar-based fertilizer for Cd²⁺was improved by 32.23%.Fourier transform infrared spectroscopy?FTIR?and X-ray diffraction?XRD?analysis showed that the adsorption mechanism mainly included ion exchange,cation-?interaction and precipitation.The hydrogen peroxide in urea peroxide makes biochar-based fertilizer produce more oxygen-containing functional groups,which provides more adsorption sites for Cd²⁺.3.The results of soil passivation test showed that compared with the control group,the acidic extractable,reducible and oxidizable Cd decreased by 3.03%,1.85%and 2.45%respectively in the contaminated soil with 2%biochar-based fertilizer after 45d,while the residual Cd increased by 2.03 times,indicating that biochar-based fertilizer had a better passivation effect on heavy metal Cd in the soil.4.The adsorption process of chlorpyrifos by biochar-based fertilizer accords with the second-order kinetics model,which indicates that the adsorption of chlorpyrifos by biochar-based fertilizer is mainly chemical adsorption.Isothermal adsorption experiments showed that Langmuir isothermal adsorption model can better describe the adsorption behavior of chlorpyrifos on biochar-based fertilizers than Freundlich isothermal adsorption model,indicating that the adsorption process is also mainly based on a monolayer adsorption behavior.FTIR of biochar-based fertilizer and chlorpyrifos showed that the adsorption mechanism was mainly cation-?interaction.Compared with biochar,the adsorption capacity of biochar-based fertilizer to chlorpyrifos increased by 33.83%.It may be attributed to the fact that hydrogen peroxide from urea peroxide produces more oxygen-containing functional groups in biochar-based fertilizers and provides more adsorption sites for chlorpyrifos.5.Soil culture experiments showed that the content of chlorpyrifos in contaminated soil decreased by 62.00%,44.00%,and 59.00%after 15 days by adding 1%,2%,and 4%biochar-based fertilizer,respectively.Compared with biochar,the decrease rates of chlorpyrifos content in soils with 1%and 4%biochar-based fertilizers increased by 7.51%and 19.60%,respectively.These results indicated that the addition of biochar-based fertilizers could enhance the adsorption of chlorpyrifos on soils.