| Acid mine drainage(AMD)is formed by the oxidation and decomposition of sulfide minerals,and generally contains high concentrations of pollutants such as sulfur,iron,and aluminum.The high arsenic coal mine area in Xingren County,Guizhou Province is one of the typical areas of coal burning arsenic poisoning in China.High arsenic coal mines and abandoned old kilns are widely distributed,and the continuously released acidic coal mine wastewater is directly discharged without treatment,causing serious pollution to surrounding farmland and crops..In this paper,through pot experiments,different proportions of unmodified biochar were applied to AMD contaminated soil to plant rice,to explore its loading mechanism on iron and arsenic,the changes in soil iron and arsenic forms,and the impact on iron and arsenic absorption and transportation by rice.The following conclusions were drawn from the study:(1)The application of biochar increased the p H,EC,Eh and water content of the soil,and increased the concentration of arsenic and ferrous iron in the soil pore water.Compared to the unapplied biochar group,The application of biochar increased the p H,EC,Eh and moisture content of the soil,And the amount of increase increases with the proportion of biochar applied,As the rice grows,The proportion of the crystalline iron-bound state(F4)arsenic and iron content in the soil has continuously decreased from tillering stage to maturity stage,Conversion to residual state and amorphous iron binding state(F3);The application of biochar promotes the dissolution of iron and arsenic in the soil into the soil solution,Significant positive correlation between arsenic and Fe()concentration in pore water,The correlation coefficients in the 3% and 5% groups were 0.86(p <0.01)and 0.95(p <0.01),respectively.(2)Biochar has a better loading effect on arsenic and iron in the soil,The proportion of each element on the surface of biochar is C > O > Fe > As;The application of biochar reduces the arsenic iron mole ratio of the stereotyped iron-bound state(F3)in the soil,Biochar surface functional groups(-SO2-,-OH and C-O,etc.)can adsorb free iron and arsenic in fixed soil solution;Iron in Fe(Ⅲ),The arsenic on biochar in 3% and 5% groups was mainly as As(Ⅲ),And As(Ⅲ)mainly complexed or coordinate with hydroxyl and group,As(V)is mainly complexed or coordinated with carboxyl and groups in organic matter.(3)The iron and arsenic content of all organs of rice showed: root> stem> leaf>rice husk> grain,and the content of arsenic and iron decreased continuously from tillering stage to maturity stage.During the ripening period,the iron content in rice grains decreased with the proportion of biochar addition,with a minimum of 0.14 g /kg,while the arsenic content showed the opposite trend but increased less.(4)The bioconcentration factors(BCF)of arsenic and iron in the parallel group of rice roots with biochar was significantly reduced compared with the unadded group,3% and 5% group decreased by 13.94% ～ 49.46% and 26.29% ～ 52.21% respectively;the tolerance index of rice roots and stems was significantly improved with the highest of 138.66.In addition,the addition of biochar also promoted the transfer of arsenic and iron in rice stems,and the size of migration factor was 5% group> 3%group> 0% group. |
