| dc.description.abstract | The harmful by-products produced by urban industrialization and economic industries need to be treated properly. However, cases of industrial heavy metal wastewater arbitrarily discharged into natural waters without careful treatment have often occurred in recent years, and this is the main reason that irrigated fields are polluted by heavy metals. Regarding the strategies for remediation of heavy metal pollution in the agricultural field, scientists have mainly studied the use of eco-friendly and low-cost soil amendments (such as biochar) for in situ stabilize heavy metals in paddy soils in recent years, and many soil amendments have been developed. Therefore, it is necessary to consider how to pre-select the appropriate soil amendments for soil remediation on a site-specific basis. In view of this, this study will use the linear model maked based on the idea of isotherm adsorption as mentioned in the relevant literature to estimate the adsorption potential of cadmium, copper, and zinc for biochars in paddy soils. The soil incubation experiment was used to observe the actual concentration changes of heavy metals in pore waters after applying different biochars. Furthermore, we will also examine the competitive effect of co-existing other heavy metals on the adsorptive interaction between synthetic BC and the target metal, and discuss adsorption mechanism as well. Five biochars were used in this study. Biochars produced from rice husk and camphor tree leaf pyrolysed at either 300 or 600 °C (RB300, RB600, LB300 and LB600, respectively). The Fe-modified biochar was produced by immersing the rice husk into a FeCl3∙6H2O solution, and then pyrolyzed at 300 °C (Fe-RB300). In the batch adsorption experiment, higher adsorption capacity of biochars synthesized at low temperature (RB300, LB300) for Cd(II), Cu(II) and Zn(II), compared to biochars synthesized at high temperature (RB600, LB600). LB300 showed a optimal adsorption capacity for these three heavy metals. As for the Fe-RB300, worse adsorption capacity for Cd(II), Cu(II) and Zn(II) compared to RB300. In addition, the adsorption capacity of most biochars toward heavy metals were in the order of Cu(II)＞Cd(II)＞Zn(II) for the multi-metal adsorption isotherm, whereas LB300 had the order of Cd(II)＞Cu(II)＞Zn(II). In the soil incubation experiment, concentrations of Cd(II), Cu(II) and Zn(II) in pore waters after different biochar treatments were all significantly lower than those in the control: LB300 was most effective for stabilizing Cu(II); LB600 was most effective for stabilizing Cd(II) and Zn(II); Biochar impregnated with iron oxides (Fe-RB300) had no apparent immobilization effect on heavy metals in comparison with the original biochar (RB300). Regarding the prediction results of heavy metal concentrations in pore waters using the linear model, most of the results showed that the linear model did not give reliable predictions in the reduction of Cd(II), Cu(II), and Zn(II) concentrations in pore waters, which might be due to the negligence of the dissolved organic matter (DOM) effect, or/and the lack of sufficiently low concentrations of heavy metals used in the aqueous adsorption experiments. Nonetheless, the modeled value was indeed closer to the observed value under RB300 and LB300 treatments when the metal competitive effect was taken into account for pore water Cd(II), and it still means that it is necessary to take the metal competitive effect into consideration. | en_US |