Effects Of Spartina Alterniflora-derived Biochar On Remediation Of Cadmium Contaminated Soil And Its Mechanisms

Cadmium Contaminated Soil?CCS?has hampered worldwide food security and human health for decades.Spartina alterniflora Loisel.?S.alterniflora?,which is recognized as an alien invasive species that has seriously degraded the Dongtan wetland in Chongming District,Shanghai,was selected as the raw material for biochar preparation in the present study.The optimum conditions for cadmium remediation by Spartina alterniflora Loisel.Based Biochar?SLB?was investigated,and the mechanisms of cadmium remediation were also explored.Furthermore,Brassica chinensis L.was used for pot experiment to evaluate the actual effect of SLB on CCS.This study could not only make a sufficient utilization of S.alterniflora,but also could provide scientific basis and important guidance for the remediation methods of CCS.The main conclusions were as follows:The influence of pyrolysis temperature on SLB was investigated.It was shown that 450?was the optimal temperature for SLB preparation.The cadmium absorption capacity of 450SLB could achieve 20.576 mg·g^-11 in only 15 min,which showed that SLB exhibited a great performance on cadmium adsorption.The adsorption of cadmium by SLB agreed well with the second order kinetic equation,which illustrated that chemical adsorption was the main adsorption pattern.Granular protrusions were emerged on the surface of cadmium-absorbed 450SLB,and hydroxyl,carboxyl and the other oxygen-containing functional groups were remarkably changed after adsorption.Cadmium was partially absorbed onto the surface of biochar,and the formation of cadmium-biochar compound system was possibly formedThe SLB was incubated with Cd?NO₃?₂ and kaolin for 15 days to simulate the CCS environment.The results showed that both SLB and kaolin accelerated the fixation of cadmium.The R_50,biochar0,biochar value increased from 48%to 53%⁵6%,indicating that the stability of biochar had improved after incubation.The changes of physical morphology and chemical structure of SLB,cadmium and kaolin after incubation were analyzed by various instrumental characterization methods,which could reveal the remediation mechanisms of CCS by SLB.The results showed that the combined effect of physical isolation,precipitation,interior complexing and iron exchange might be the main mechanisms of CCS remediation by SLB.Brassica chinensis L.was used in the pot experiment to evaluate the actual effect of SLB on CCS.The results showed that cadmium stress could reduce the content of several important soil enzymes,affected soil nutrient conversion,and blocked the electron transport chain of plant photosynthesis,thus causing significant damage for soil quality and plant growth finally.SLB was able alleviate the cadmium stress effectively and reduce the uptake of cadmium by plants,thereby restoring the normal function of soil.SLB also played an important role in nutrient transportation,thus improving the soil quality and promoting the growth of plant.