Biochar Passivation Of Pb And Cd In Organic Manure And Its Field Application

Promoting the application of organic fertilizer is an important measure to fertilize black soil and improve its nutrients,which plays an important role in p romoting the sustainable utilization of black soil.Organic fertilizers often contain a variety of heavy metals,which will inevitably bring heavy metals into the environment after long-term application,leading to the accumulation of heavy metals in the environment and potential ecological risks.Therefore,safe application of organic fertilizers is of great significance to reduce the environmental risk of heavy metals caused by organic fertilizers.Biochar is a functional material with good binding capacity to heavy metal ions,so this study focused on the adsorption characteristics of biochar to heavy metal lead and cadmium and its stabilizing effect on heavy metals in cow manure.The effects of biochar combined with organic fertilizer on alleviating heavy metal accumulation,improving soil nutrients and crop growth were investigated through in-situ field experiments.The main results are as follows:(1)The adsorption characteristics of Pb and Cd by biochar showed that the adsorption equilibrium of lead and cadmium by biochar reached at 8h,and the adsorption capacities were 91.14 mg/g and 34.38 mg/g,Respectively.The kinetic adsorption process of Pb and Cd by biochar is more in line with the second order kinetic model.The results of isothermal adsorption fitting showed that the isothermal adsorption of Pb and Cd by biochar more conforms to the Langmuir equation,indicating that the adsorption of Pb and Cd by biochar is a monolayer adsorption.Fourier infrared spectroscopy(FT-IR)shows that the surface of biochar contains hydroxyl group(-OH),carboxyl group(-COOH),carbon-oxygen single bond(C-O)and carbon-oxygen double bond(C=O),which provide a large number of binding points for the adsorption of biochar.(2)The aging effects of Pb and Cd in organic fertilizers under different biochar ratios were investigated.With the increase of aging time and the proportion of biochar added,the content of Pb and Cd in organic fertilizer decreased gradually.During the whole aging period of 5-35 days,the effective lead content in organic fertilizers treated with 5%,10% and 20% biochar decreased by 4.25%-25.91%,11.77%-39.70% and 16.04%-53.39%,Respectively,compared with the control group.The effective cadmium content decreased by 5.58-10.38%,13.40%-29.57% and 17.14%-34.76%,Respectively.Combined with the changes of nutrients in the biocharcoal-organic fertilizer mixture and the effective contents of Pb and Cd,the final determination of the dosing ratio of biochar of 10% and the aging time of 25 days can give consideration to t he basic requirements of heavy metal availability regulation,nutrient maintenance and production convenience.Under the above conditions,the effective state contents of lead and cadmium in the biochar and organic fertilizer mixing system were 5.42 ± 0.27mg/kg and 0.173 ± 0.01mg/kg Respectively,the mass fraction of organic matter was 55.80±2.36%,the total nitrogen was 22.02±1.21g/kg,and the total phosphorus content was 11.42±0.56g/kg.(3)The accumulation of Pb and Cd in soil and maize plants was investigated by field in situ test.The results showed that the soil effective lead content ranged from 3.31 ±0.10mg/kg to 3.86±0.14mg/kg at seedling stage when the organic fertilizer dosage was 550-1006 kg/mu.The effective cadmium content ranges from 0.23±0.01mg/kg to 0.28±0.01mg/kg.At the same nutrient addition level,the effective lead content of soil treated with biochar combined with organic fertilizer ranged from 3.31±0.03mg/kg to 3.67±0.14mg/kg.The effective cadmium content ranges from 0.20±0.01 to 0.25±0.01mg/kg.Compared with the single application of organic fertilizer,the effective lead content decreased by 0.03%-8.57%.The effective cadmium content was reduced by 12.97-15.96%.At the maturity stage,the effective content range of heavy metal lead in soil treated with biochar combined with organic fertilizer ranged from 3.04 ± 0.16mg/kg to 3.23 ±0.24mg/kg.The effective content of cadmium ranged from 0.14 ± 0.02mg/kg to 0.18 ±0.02mg/kg.The effective content of lead in soil was reduced by 4.8%-13.31%.The effective content of cadmium decreased by 9.57%-22.40% Respectively.By comparing the changes of heavy metal contents of Pb and Cd in soil treated with different fertilization in two maize growing periods,the passivation effect of heavy metal in seedling stage with biochar wa s better than that in mature stage.With the increase of fertilizer,the lead content of maize plants treated with organic fertilizer increased from 0.95±0.12 mg/kg to 1.35±0.10 mg/kg.Cadmium content ranges from 0.22±0.03mg/kg to 0.27±0.01 mg/kg.The lead content of maize plants treated with horizontal biochar and organic fertilizer was 0.83± 0.11mg/kg-1.14±0.09mg/kg.The cadmium content was 0.22±0.02mg/kg-0.26±0.03mg/kg.Compared with the single application of organic fertilizer,the lead content decreased by 15.19%-17.78%.Cadmium content decreased by 2.9% to 7.9%.(4)Based on the investigation of heavy metal accumulation,the physical and chemical properties of soil and the nutrient accumulation and changes of the tested plants(maize)were further investigated.Results show that with the increase of fertilizer dosing quantity(550 kg/mu-1006 kg/mu),contrast analysis of the different fertilizer treatments within the test area of soil p H,organic matter content,soil total nitrogen(TN)content,soil total phosph orus(TP)content,soil alkaline hydrolysis nitrogen content,soil available p content and total nitrogen(TN)content of corn crop and the contents of total phosphorus(TP),it is concluded that biochar with organic fertilizer is better than that of single organic fertilizer.However,there was no significant difference between the two fertilization methods.With the increase of fertilizer,the yield per unit area of experimental corn increased.The yield range per mu of single application of organic fertiliz er was 617.8±65.9kg/ mu-707.9±52.1kg/ mu,and the yield range per mu of biochar was 621.10±58.2kg/ mu-712.37±29.5kg/ mu,which was 0.71-15.39% higher than that of the former.Considering the effect of heavy metal passivation and economic factors,the suit able application amount is 660 kg/mu of organic fertilizer.