Preparation Of Hang Biocharcoal-based Composite Fertilizer And Its Remediation Effect On Cadmium Pollution In Farmland Soil

Cadmium pollution in soil will not only affect soil ecosystem,inhibit plant growth,reduce crop yield and quality,but also threaten human health easily through food chain accumulation.In1984,the United Nations Environment Programme explicitly listed cadmium as one of the most important agricultural environmental pollutants.With the increasing pollution of cadmium in soil and the increasing demand for safe food,searching for a low-cost,high-efficiency and fertile passivation technology of farmland soil has become a research hotspot in recent years.Biochar and its composites have rich active functional groups,complex pore structure,large specific surface area and cation exchange capacity,which make it possible to passivate heavy metals in soil and improve farmland fertility.B5PNx series and B10PNx series biocharcoal-based compound fertilizer were prepared from corn straw biomass and diatomite and loaded with nutrient elements?N,P?,and their physicochemical properties and microstructures were analyzed.The effects of Biocharcoal-based compound fertilizer on the passivation and improvement of cadmium-contaminated soil and the growth of maize were studied based on soil incubation experiments in laboratory and maize planting experiments in field.The main research contents and results are as follows:1)Basic physical and chemical properties and microstructure of biocharcoal-based compound fertilizer.Compared with single biochar Bx,B5PNx series belongs to neutral material?pH:6.91⁷.14?,B10PNx series belongs to weakly alkaline material?8.01-8.74?.Based on functional group analysis,B5PNx series and B10PNx series have more aliphatic C-O stretching,Si-O-Si,PO₄^3-,amino groups and other active functional groups than Bx series.The B5PNx and B10PNx biocharcoal-based compound fertilizer belong to mesoporous structure?2nm<d<10nm?,the pore size is only about 2 nm,and the specific surface area is obviously larger than that of Bx biochar.The contents of P,N and Si elements in B5PNx and B10PNx increased in different degrees after biomass was mixed with diatomite,calcium heavy superphosphate and urea.Based on the microstructure of SEM,B5PNx and B10PNx mainly show that the lamellar structure of fish scale and honeycomb bone structure are arranged disorderly,which is obviously different from the flake structure of Bx biochar.2)The deactivation effect of biocharcoal-based compound fertilizer on soil Cd was studied based on laboratory soil cultivation experiment.The results showed that the passivation effect of biocharcoal-based compound fertilizer on soil Cd increased with the increase of pyrolysis temperature.When the pyrolysis temperature is 600?,the average deactivation rate of soil Cd is the highest?34.02%?.The passivation effect of B5PNx series on soil Cd was the best under different raw materials ratio,and the average deactivation rate was 34.43%.The deactivation rate of Biocharcoal-based compound fertilizer B5PN₆ to cadmium was 41.2%,which was 1.45 times higher than that of biochar,when the dosage of biochar material was 3%,and the passivation rate of soil was increased with the increase of the dosage of biocharcoal-based compound fertilizer,and the average deactivation rate of Biocharcoal-based compound fertilizer was 41.2%.Based on performance characterization and deactivation effect analysis,the passivation mechanism of biocharcoal-based compound fertilizer to soil cadmium is mainly through compound diatomite,calcium superphosphate,urea and other materials to increase its surface functional groups?siloxyl,alkoxy,amino,amino?groups,such as diatomite,calcium superphosphate,urea etc.Carboxyl group,etc.)and surface minerals?phosphate,carbonate,etc.?make it complexate with cadmium ion in soil,precipitate and so on,and then change the form of cadmium in soil and make cadmium deactivation.At the same time,the complex pore structure of biocharcoal-based compound fertilizer provides more shadow pores and adsorption sites,which can further lock up cadmium and improve the stability of deactivation cadmium in biocharcoal-based compound fertilizer.3)The environmental effects of biocharcoal-based compound fertilizer on soil and crop system were analyzed based on field experiments.The results showed that the ratio of available content of cadmium to total content of cadmium in soil decreased significantly with the increase of biocarbon compound fertilizer application,and the ratio of available content of cadmium to total content of cadmium in soil was significantly decreased with the increase of Biocharcoal-based compound fertilizer application.The percentage of available cadmium in soil was the lowest?31.43%?when the application rate was 1800kg?ha^-1.Under different raw materials ratio,the average available state of Cd in farmland soil was the lowest?33.15%?when B5PNx series biochar materials were applied.When biochar materials were prepared at 600?at different pyrolysis temperatures,the average percentage of available Cd in farmland soil was the lowest?34.68%?.At the same time,the application of biocharcoal-based compound fertilizer significantly increased the organic matter and cation exchange capacity of farmland soil.After applying B5PN₆ biocharcoal-based compound fertilizer according to 1800kg?ha^-1,the soil organic matter and cation exchange capacity were significantly increased.The organic matter content and cation exchange capacity of farmland soil were 2.89%and 12.93cmol?g^-1,respectively.Soil organic matter?2.21%?and cation exchange capacity(10.76cmol?kg^-1)of Bx series were 1.3 times and 1.2 times as much as that of soil organic matter and cation exchange capacity(10.76cmol?kg^-1),respectively.4)The bioavailability of biocharcoal-based compound fertilizer to cadmium in soil-crop system was analyzed based on field experiments.Compared with the control,the cadmium content of maize grains treated with different treatments(450kg?ha^-1,900kg?ha^-1,1800kg?ha^-1)decreased by16.67%,26.19%and 30.95%,respectively.The cadmium content of corn grain treated with different raw material ratio?Bx,B5PNx,B10PNx?decreased 23.38%,21.43%and 26.19%,respectively.Under different pyrolysis temperatures?300?,450?,600??,the Cd content of corn grains decreased by 16.67%,21.43%and 33.33%,respectively.Compared with Bx biochar,the Cd concentration coefficient of maize grain was significantly decreased after applying biocharcoal-based compound fertilizer.The average enrichment coefficient of B5PNx Biocharcoal-based compound fertilizer was 0.34%,which was 10.53%lower than that of Bx biochar?0.38%?.The biocharcoal-based compound fertilizer with 1800kg?ha^-1 had the best effect.Based on the properties of biochar materials,the results of laboratory and field experiments show that when biomass and diatomite,the mass ratio of superphosphate to diatomite is 5:1:1.The B5PN₆ biocharcoal-based compound fertilizer prepared at 600?has the best environmental effect on soil and crop system.Therefore,the preparation conditions of biocharcoal-based compound fertilizer were determined as follows:corn straw biomass,diatomite and calcium heavy superphosphate mixed at 5:1:1 and pyrolysis at 600?in oxygen-free atmosphere.Then mix with urea 4:1 and bake for 3 hours.