The Mechanism Of Biochar-Iron Oxide Nano-composites On Immobilization Of As In Paddy Soils

Iron?hydro?oxides composites are the effective adsorbent for As in the environment,so iron?hydro?oxides composites can be applied for reducing the availability of As for uptaking by rice in the remediation of As-polluted paddy soil.The biochar-iron oxide nano-composites?BION?was prepared with the same palm fiber and Fe?NO₃?₃.Firstly,a chemical stabilization experiments were conducted to compare the stabilization effects of biochar,Fe?NO₃?₃ and BION in wastewater treatment of As.Secondly,pot culture experiments and field culture experiments were conducted to investigate the effects of the three materials on As availability and its uptake by rice.Finally,the effects of BION on the removal and transformation of As were also studied to explain the control mechanisms of BION on As uptake by rice.The results were as follows:?1?The characterization analysis showed that iron nanoparticles were uniformly decorated and firmly anchored on the porous biochar layers.The BION showed the excellent adsorption of As???from aqueous solution.The experiments revealed that the adsorption capacity of BION was much better than that of biochar.The maximum adsorption capacity of BION for As???at pH 4.0,7.0 and 9.0 were 15.605 mg g^-1,16.223 mg g^-1,10.918 mg g^-1,respectively.BION might be a useful alternative adsorbent of As???from the aqueous solution.?2?In the pot experiments of seven treatments,As concentration decreased from iron plaque to brown rice,it followed iron plaque,root>>straw>hull>brown rice.There were significant correlations between As in each portions of rice,As and Fe in iron plaque.?3?In the seven different treatments,the concentrations of Fe²⁺and Fe³⁺in pore water increased with the growth stage.In the four growth stage,there were significant correlations between the concentration of Fe²⁺and the concentration of As in pore water,negative correlations between the concentration of As in pore water and the concentration of Fe in iron plaque,and the positive correlation between the concentration of As in pore water and the concentration of As in each portions of rice plant.The correlation relationships strengthened through the growth stage with seedling stage<tillering stage<filling stage<maturation stage.?4?Compared with biochar,the concentrations of As in soil and brown rice decreased significantly when the soil was treated with BION.The application of BION in the contaminated soil could raise the rice output and decrease the accumulation of As by rice.