Effects Of Modified Biochar Application On Speciation Of Arsenic And Soil Enzyme Activity In Arsenic Contaminated Soil

In recent years,the problem of heavy metal pollution is a growing concern in environmental protection.Arsenic pollution is seriously threatening people's health and life safety.At present,the remediation and safe utilization of heavy metal contaminated soil are key problems in the field of agriculture and environment in the world.The industrialization and application of biochar have attracted attentions of scholars,which plays an important role in the remediation of pollution.In this study,the pine biochar and pine biochar with iron loading were used as experimental materials.Adsorption mechanisms of arsenic on modified biochar were investigated by adsorption tests.Pot experiments were designed to explore influence of the modified biochar on arsenic bioavailability and enzymatic activity in soil.The main conclusions are listed below:(1)SEM analysis showed that the modified biochar had basically skeleton structure as the original pine biochar and with small particles crystal on the surface.FTIR analysis showed that the types of organic functional groups of modified biochar were almost unchanged and the characteristic peak of Fe appeared on the surface,mainly for Fe-OH and Fe-O.The absorption peak shape was basically unchanged but migrated after As(?)was absorbed on modified biochar,which indicated that the biochar material had ligand exchange reactions with the As(?).Compared with the iron content of pine biochar,that of modified biochar increased significantly.The rank of iron content was PBC-A > PBC-C > PBC-B >PBC-D,and the highest iron content was 2.78%.(2)The adsorption of As(?)by the pine biochar and modified biochar has shown that the progress of adsorption was perfectly fit to the adsorption kinetics quasi-two equation.The theoretical equilibrium adsorption quantity was in good agreement with the experimental equilibrium adsorption.The adsorption isotherm of pine biochar and modified biochar to As(?)conformed Freundlich isotherm equation.These results indicated that the adsorption system was the combination of monolayer covering and multilayer adsorption,which mainly controlled through physical adsorption and chemical adsorption.The arsenic adsorption capacity of PBC-A and PBC-C were 7.44 and 7.37 times than pine biochar,so subsequenttrials in this study selected PBC,PBC-A and PBC-C.(3)Pot experiment indicated that the arsenic in soil existed mainly amorphous and weakly crystalline Fe-Al oxide binding state and crystalline Fe-Al hydration oxide binding state,while.applying all the treatments of modified biochar could significantly reduce the content of effective state,the non specific adsorption state,the special adsorption state,the amorphous and the weakly crystalline Fe-Al oxide binding state arsenic.When adding 4%PBC-A and PBC-C to arsenic contaminated soil,the most effective arsenic content in soil were lower than that of PBC,and they had the best passivation effect on arsenic.Modified biochar significantly reduced the arsenic content in cabbage.The study indicated that modified biochar can effectively reduce the mobility and bioavailability of arsenic in soil,and reduce the biological toxicity of arsenic.(4)In arsenic contaminated soil,with the increase of addition of modified biochar,soil urease,catalase and alkaline phosphatase activity increased,and the enzyme activity were higher than that of PBC.When 4% modified biochar PBC-A and PBC-C were added,alleviate the inhibitory effect of arsenic on urease,catalase and alkaline phosphatase were the best;Adding modified biochar PBC-A and PBC-C,the invertase activity in soil increased first and then decreased,and when 1% modified biochar PBC-A and PBC-C were added,the invertase activity was higher than that of PBC,alleviate the inhibitory effect of arsenic on invertase was best.