Study On The Effect Of Biomass Charcoal And Its Aging On The Adsorption And Fixation Of Cadmium In Tea Garden Soil

With the aggravating contamination of heavy metals,the remediation of contaminated soil has become one of big concerns currently.The application of soil amendments to solidify heavy metals,increase soil fertility,and promote crop growth is an important measure for the rehabilitation of agricultural contaminated soils.Among the many soil amendments,because of its special structure and property,such as huge specific surface area,being rich in oxygen-containing functional groups and a large number of surface charges,biochar could be an alternative absorbatent.In recent years,biochar has been widely used in the repair of heavy metal contaminated soils.To explore different biochar effect and immobilize heavy metal pollution in tea garden soils,in this paper,the normal agricultural wastes in North of China,wheat straw and chicken manure were chosen.Four biochar were prepared at different pyrolysis temperatures?350?&650??using wheat straw and chicken manure as raw materials,labeled as M350,M650,F350 and F650.The composition of biochar were characterized by FTIR transform infrared spectroscopy,X-ray diffraction and elemental analysis.Adsorption characteristics of Cd²⁺by these biochar at different sorption times,pHs,and Cd²⁺concentrations were investigated by batch equilibrium experiments.Batch equilibrium experiment and soil column leaching experiment were conducted to investigate the effects of biochar on adsorption of Cd²⁺onto tea garden soils,and the feasibility of using biochar to remediate the cadmium contaminated tea garden soils was assessed.The primary results are as follows:?1?The pH,ash content,aromaticity and hydrophobicity of the biochar increased with the increasing of pyrolysis temperature,and the polarity decreased.At the same temperature,the chicken-manure-derived biochar had higher pH and ash contents than the wheat-straw-derived biochar,and the aromaticity was more complete.The oxygen functional groups of the four biochar are basically the same,except that their functional groups are slightly different in abundance.With the increase of pyrolysis temperature,the functional groups such as aliphatic,hydroxyl,phenolic hydroxyl and carboxyl in biochar gradually decreased or even disappeared,and aromatic functional groups gradually increased.?2?The sorption kinetics of Cd²⁺onto biochar could be fitted with the pseudo second order kinetic model?R²>0.99?,and the time required to reach sorption equilibrium was 12 hrs.Furthermore,the sorption processes were controlled by external liquid film diffusion,surface adsorption and intraparticle diffusion,and the latter was found to be the rate-controlling step.As the solution pHs increased from 2.0 to 6.0,the amount of Cd²⁺adsorbed on the biochar gradually increased,and achieved the maximum at pH 6.0.Adsorption isotherms for wheat-straw-derived biochar were fitted the Langmuir model more effectively than other models?R²,0.9703⁰.9815?,Chicken-manure-derived biochar was more suitable for Freundlich model?R²,0.9703⁰.9815?.At the same temperature,the adsorption effect of chicken-manure-derived biochar is better than wheat-straw-derived biochar.?3?Wheat-straw-derived biochar and chicken-manure-derived biochar of Cd²⁺are a variety of mechanisms of mixing.For 650?biochar,cation-?interaction and precipitation were the dominant sorption mechanisms.For 350?biochar,the electrostatic interaction and precipitation may be the dominant sorption mechanisms.?4?The adsorption capacity of Cd²⁺in tea garden soils increased with the application of biochar.Compared with CK1,the adsorption capacity of Cd²⁺increased by 10%-70%and17.5%-95%in tea garden soils with different biochar application amounts?0.1%?0.5%and 1%,w/w?of wheat-straw-derived biochar and chicken-manure-derived biochar,respectively.The Cd²⁺adsorption capacity of tea garden soils with aged wheat-straw-derived biochar and chicken-manure-derived biochar decreased by 22%and 14%,respectively,than that of tea plantation soils with fresh biochar.Application of biochar increased the pH value of soils leaching solution and decreased the leaching of Cd²⁺in contaminated tea garden soils.Compared with CK2,the cumulative leaching amounts of Cd²⁺in tea garden soils with wheat-straw-derived biochar and chicken-manure-derived biochar decreased by 36.75%and 86.81%,respectively.These results suggest that the application of two types of biochar significantly improve the soil buffering capability and the retention capacity metals in tea garden soils,in which the effect of chicken-manure-derived biochar is more obvious.