Abstract:

Biochar pyrolysis at high temperature with limited oxygen plays an important role in the resource utilization of agricultural waste, carbon sequestration and emission reduction, indicating the great potential of biochar for remediating contaminated environment. As a functional material for soil remediation, its ability of adsorption and fixation for heavy metals is still insufficient, which limits the large-scale promotion and application of biochar. Nowadays, it has been an increasingly important research area to enhance the adsorption and fixation capacity of biochar through modification design of engineered materials. In this study, wood chips were used as raw materials to prepare biochar (BC), and then lanthanum modified biochar (LBC) was manufactured. Aiming to remediate arsenic contaminated red soil and compare the immobilization difference, these two kinds of amendments (LBC, BC) were applied into the experimental soils separately, and the blank soil without material addition was used as control treatment. All these above treatments was cultivated for 30days under the soil moisture content with 30%, 70%, and 100% field water capacity respectively, and the corresponding remediation effects of arsenic contaminated red soil by using LBC and BC were investigated. The results were as following: (1) LBC addition was beneficial for alleviating the acidification of southern red soils. When the cultivation experiment was finished, soil pH treated by LBC was enhanced obviously and the increased pH ranged from 0.86 to 1.20 units under three kinds of soil moisture content with 30%, 70%, and 100% field water capacity. In comparison with BC treatment, the soil pH also increased by 0.09−0.44 units after LBC addtion. (2) LBC application led to the obvious immobilization effect of arsenic in red soils, and the related fixation efficiency under three kinds of soil water content was up to 54.7%−90.0% during the whole soil cultivation period, and the immobilization efficiency reached 81.0%−85.8% after 30days of cultivation. On the contrary, soil treated by BC resulted in the arsenic activation of soils with the increased percent 135.4%−895.9% compared to the control. (3) The immobilization effect of LBC on soil arsenic is mainly related to the transformation of arsenic in various speciation, especially from non-specialized adsorption forms to more stable ones such as residue forms. In the meanwhile, BC resulted in the enhancement of non-specialized adsorption arsenic and promoted the activation of soil arsenic. (4) LBC was capable of immobilizing arsenic in red soils with high efficiency, and did not obviously excert negative influence on soil enzyme activity. The application of LBC was able to improve the activity of soil urease and catalase although it led to a slight decrease in soil phosphatase and sucrase activities. It is worth mention that LBC treatment remained higher soil sucrase activities than those for BC treatments. Overall, it manifest that LBC has great potential for remediating arsenic contaminated red soil.

Key words:

Bioch ar, Red soil, Arsenic, Passivation, Enzyme activity