| Chemical leaching is one of the practical techniques for the remediation of heavy metal contaminated soils,the timely improvement of the soil after leaching and the restoration of the original ecological functions of the soil as much as possible are of great significance to the value of soil resources and the maintenance of the safety of the ecosystem.In this paper,the mining area soil contaminated by Mn and Cd is used as the research object,the re-aggregation effect of soil aggregates and the change characteristics of the occurrence of heavy metals during the improvement process after citric acid and FeCl3 leaching and using CaO,corn stalk biochar or chicken manure fermented organic fertilizer were investigated,a comprehensive analysis of the effects of different amendments on the organic matter,total nitrogen content,microbial community structure,mineral phase composition and surface micro-morphological characteristics of soil aggregates,reveals the damage/aggregation mechanism of different leaching agents and amendments to the structure of soil aggregates,and evaluates the quality of the soil after leaching and improvement,so as to provide a reference for the reuse of heavy metal contaminated soils.The main research conclusions are as follows:（1）Both citric acid or FeCl3 leaching can effectively reduce the mass concentration of Mn and Cd in the soil,but the residual heavy metal activity in the soil is at a higher level after leaching.Soil leaching caused serious damage to the structure of soil aggregates,the proportion of large aggregates of 0.25-2.00mm decreased by 1.28%～4.09%compared with the control,and the proportion of powder clay particles of<0.05mm increased by 30.68%～41.50%,indicating that the chemical leaching greatly reduces the stability of soil aggregates.（2）The addition of the modifier reduces the content of the weak acid extractive state of residual heavy metals in the soil after leaching,and the activity of heavy metals is effectively controlled.Among them,the amendment CaO has a good passivation effect on Mn,but excessive CaO activates the residual Cd in the soil,and the biochar amendment shows the passivation of Mn and the activation of Cd in the soil after FeCl3 leaching.The organic fertilizer modifier has a long-term passivation effect on Mn and Cd,and there is no activation of heavy metals.（3）CaO has an outstanding effect on stabilizing soil aggregates after leaching in a short period of time,greatly reducing the proportion of aggregates<0.05mm in the soil.Biochar does not have a significant effect on the aggregation of aggregates in the soil after leaching with citric acid and FeCl3,which is mainly due to the limitation of the soil environmental conditions after leaching and the slower decomposition of biochar.Organic fertilizer has a good agglomeration effect on soil aggregates after FeCl3 leaching,but has a poor stabilization effect on soil aggregates after citric acid leaching.（4）The content of organic matter and total nitrogen in the soil cannot be used as indicators for judging the stability of soil aggregates,it should be judged more scientifically by organic matter with binding effect or bioavailability.The microbial community structure has a certain correlation with the stability of soil aggregates.Compared with citric acid leaching,FeCl3 has less impact on the microbial community structure and cohesive minerals such as kaolin.After FeCl3 leaching,chicken manure fermented organic fertilizer has the best soil improvement effect,which is more conducive to the restoration of soil ecological functions.（5）When improving the soil after chemical leaching,the indicators that affect the stability of soil aggregates should be fully considered,after comprehensively analyzing the soil organic matter,microbial community structure,mineral composition and the properties of amendments,apply them rationally,and pay attention to the changes in the form of residual heavy metals to restore the original ecological functions of the soil. |
