Study On The Effect Of Amendments On Soil Cd Pollution Remediation And Water Movement Characteristics

In recent years,with the rapid development of China’s economy and significant breakthroughs in urbanization and industrialization,heavy metal pollution has become a critical issue that needs to be addressed urgently in the country.Among them,cadmium（Cd）,a heavy metal with high mobility and concealment,is a particularly concerning pollutant element.With the application of soil amendments and the reduction of immobilized heavy metals minimizing crop uptake,whether the addition of amendments to the soil infiltration,porosity,water-holding capacity and other conditions due to the addition of amendments,as well as the potential pollution hazards to groundwater from leaching of immobilized heavy metals under natural conditions such as rainfall also require further research.This experiment simulated the long-term flooding conditions in paddy fields through pot experiments.It studied the effects of five amendments:ferrous sulfate（FS）,rice husk biochar（BC）,calcium carbonate（LS）,zero-valent iron（n ZVI）,and iron-manganese modified biochar（FMBC）on the growth and Cd absorption capacity of rice（Mengliangyousimiao）under different additions（mass fractions of 2‰,4‰,and 6‰）.The soil column leaching test was also conducted to investigate the leaching characteristics of different amendments on soil infiltration,water holding capacity and Cd²⁺.The results showed that:（1）Compared with the control group（CK）,the addition of five amendments added significantly changed the physicochemical properties of the soil.Except for FS,all amendments significantly increased the soil p H by between 0.26 and 0.98 units,and the increase in p H contributed to the passivation of Cd.（2）Compared with CK,the addition of BC,LS,n ZVI,and FMBC all significantly reduced the Cd content in rice roots,stems and leaves and brown rice to below the limit value(0.2 mg·kg^-1)standard for Cd specified in the National food safety standard Maximum levels of contaminants in foods（GB 2762-2017）.The Cd content in the roots,stems and leaves of rice in the FMBC group was comparable to the levels before modification.FS reduced the soil p H,increased the effective Cd content of the soil,and the Cd content in the roots,stems and leaves and brown rice of rice also tended to increase,which indicates the passivation effect wasn’t adequate.（3）BC,LS,FS,n ZVI,and FMBC can significantly reduce the soil water capacity,with LS showing an increasing trend with increasing addition.BC,LS,and FMBC reduced the wetting front migration distance and cumulative infiltration,thus inhibiting soil water infiltration,while FS and n ZVI had the opposite effect.The water characteristic curves of the five amendments generally shifted to the right,indicating an increased water-holding capacity of the soil.Among them,the water holding capacity of BC,LS and FMBC increased with increasing addition,while the trend of FS and n ZVI did not change significantly.All five amendments increased the total soil porosity and the number of small and medium soil pores,among which LS was effective in increasing soil porosity.（4）The Cd²⁺content of the soil leachate under the conditions of the five amendment additions all met the groundwater quality standards in China’s quality standard for ground water（GB/T 14848-2017）for Class II water quality,indicating the long-term effectiveness of inhibiting Cd migration in the soil.Among them,the trend of Cd²⁺release from soil leachate after BC,LS,n ZVI and FMBC remediation was relatively stable,while the FS group took a longer time to reach a stable point and the release tended to increase with a higher addition level.Using the stepwise regression analysis equation,it was found that p H and organic matter content played a main role in Cd²⁺release,with p H having the largest determining effect and a coefficient of determination of 0.441.