The Effects Of Biochar On Immobilization Remediation Of Soil Contaminated By Cadmium

Soil heavy metal pollution, a worldwide environmental problem, has been paid more andmore attention. Biological activated carbon, known as biochar, refers to a kind of stable biomassobtained from the solid material such as corn straw by thermal cracking of hypoxic or anoxicconditions. Due to containing large amounts of phenolic hydroxyl, carboxyl and carbonyl group,biochar is of the good properties of adsorption and stability. In the paper, the adsorptionmechanism of Cd in/on biochar and the effects of biological carbon remediation on soilenvironmental quality and the cadmium content in rice were studied by laboratory simulation andfield test systematically. The studies may be provide theoretical basis for the application of cornstraw biochar in situ remediation of heavy metal pollution in soil.The results from the laboratory simulation of adsortpion indicated that the thermodynamicsadsorption characteristics of Cd2+on biochar could be discribed by Langmuir isotherm. Therefore,the maximum adsorption amounts of Cd2+at different temperatures obained from Langmuirisotherm were18.49mg·g-1(288.15K),23.51mg·g-1(298.15K),23.59mg·g-1(308.15K) and24.43mg·g-1(318.15K), respectively. The adsorption process reached equilibrium within40minutes and the dynamics adsorption characteristics of Cd2+on biochar were discribed by pseudosecond order kinetic model significantly. The pH had a significant effect on the adsorption of Cd2+on biochar when the medium solution pH ranged from2to9, however, the adsorbent particle sizehad no significant effect on the adsorption of Cd2+. According to the results of XRD, FTIR andXPS, the sorption mechanisms of Cd on biochar could be explained as hydroxyl groups (-C-OH)and carbonyl groups (-C=O) participate in Cd2+sorption onto biochar.The results from the field experiment indicated that the cadmium content of root, straw, leaf,shell and grain of rice reduced significantly by4.36%-17.57%,17.69%-32.31%,5.51%-22.79%,5.88%-41.76%and37.70%-73.77%, respectively, under the treatments of adding differentamount of biochar only and mixed fertilizer of biocarbon and organic fertilizer compared with thecontrol. The soil pH increased by the units of0.23-0.29under the treatments of biochar only, anddecreased with increasing the amount of biochar and organic mixed fertilizer, but all were higherthan that of the control, however, the organic fertilizer treatment decreased soil pH, which werelower than that of the control. Compared with the control, the available Cd concentrations in soils for all the treatments significantly reduced by9.65%-43.73%, and moreover, there were highlysignificant positive correlation between Cd concentrations in the root, straw, leaf, shell and grainof rice and the available Cd concentration in soils, and negtive correlation between Cdconcentrations in the root, leaf and shell of rice and soil pH was obtained, but the correlationbetween the available Cd contention in soil and soil pHwas not significant.Compared with the control, the urease activity, catalase activity and acid phosphatase activityin the soils increased distinctly by70.28%-231.87%,15.38%-31.59%and231.87%-15.38%,respectively, under the treatments of adding different amount of biochar only and mixed fertilizerof biocarbon and organic fertilizer. Moreover, the contents of available Fe, Mn, Cu and Znincreased by40.45%-271.9%,51.68%-322.3%,5.75%-62.09%,63.67%-1378%and thecontents of NH4+-N, NO-3-N, available P, available K, available Mg and available Ca increasedby44.82%-44.82%,8.69%-52.55%,19.31%-81.04%,50.01%-622.2%,26.13%-369.7%and26.13%-26.13%, respectively, for the all treatments.