Research On The Remediation Effects Of Cd Contaminated Soils By Combined Applications Of Amendments

Cadmium（Cd）contamination in agricultural soils becomes server and server in recent years.Cd not only affects crop yields and safety,but also threats human health through the food chain.Due to great remediation efficiency and simple operation,in situ immobilization remediation technology makes it appropriate for the remediation of large area of soils contaminated by heavy metals.As affected by soil type,and the type and application method of amendments,the selection of amendments type and corresponding application method for different contaminated soil is the key to better remediation efficiency.The adsorption characteristics of biochar,fly ash and white marble were studied by a series of adsorption experiments.The effects of different combinations of the three amendments on remediation efficiency of Cd contaminated soils were further investigated through soil culture experiment,pot experiment and field experiment.The main results are presented as follows:（1）The adsorption of Cd²⁺by biochar,fly ash and white marble were fitting well with the Freundlich model and pseudo-second-order model.The adsorption process is the result of physical adsorption and chemical adsorption.The saturated adsorption capacity of the three amendments were 50.61 mg g^-1,47.79 mg g^-1 and 42.92 mg g^-1.It was found that the adsorption degree and affinity of fly ash were greater than biochar,followed by white marble.The adsorption rate of biochar was greater than white marble,followed by fly ash.The adsorption of Cd²⁺by biochar and white marble increased first and then decreased with increasing p H from 3.5～8.5.The adsorption of Cd²⁺by fly ash increased with increasing p H.The adsorption of Cd²⁺by biochar,fly ash and white marble reached the maximum at p H of7.5,8.5 and 6.5,respectively.（2）The different combined application of the three amendments significantly increased soil p H and reduced the available Cd concentrations.After 30-day incubation,the p H of neutral and acidic soils increased by 0.26～0.26 and 0.23～1.32 units,respectively.Available Cd in neutral and acidic soil decreased by 10.52%～25.62%and 8.47%～32.66%,respectively.Available Cd in the two soils decreased first and then showed no significant changes with increasing incubation time.Available Cd in neutral soil showed greater decrease from 0～3days,and then showed little difference from 9～15 days.Available Cd in acidic soil showed greater decrease from 0～5 days,and then showed little difference from 7～15 days.The combination of“1.5%biochar+1.5%fly ash+0.5%white marble”and“1.5%biochar+0.5%fly ash+1.5%white marble”presented the greatest remediation efficiency for the neutral and acidic soils,respectively.（3）For the pot experiment,the different combined applications of the three amendments significantly increased the p H of neutral and acid soils,and reduced available Cd in neutral and acid soils by 7.24%～25.98%and 9.46%～24.41%,respectively.Among treatments,the growth of cabbage was inhibited when applied with higher amount of white marble and lower amount of biochar,while the growth of cabbage was not inhibited for other combined applications of the three amendments.Cd concentrations in edible parts of cabbage grown in neutral and acid soils decreased by 9.47%～22.52%and 9.10%～24.39%among different combined applications of the three amendments.With the evaluation index of Cd concentration in edible parts,the combination of“1%biochar+0.5%fly ash+1%white marble”,“0.5%biochar+1.5%fly ash+1.5%white marble”,“1.5%biochar+1%fly ash”,“1%biochar+1%fly ash+0.5%white marble”and“1.5%biochar+1%white marble”,“1%biochar+0.5%fly ash+1%white marble”,“1%biochar+1%fly ash+0.5%white marble”presented the greatest remediation efficiency for the neutral and acidic soils,respectively.（4）Under field conditions,three-season plantation of cabbage was conducted with combined applications of the three amendments.The combined applications of the three amendments kept the normal growth of cabbage by increasing soil p H and decreasing available Cd in soils.Cd concentrations in edible parts of the three-season cabbages decreased by 12.60%～29.28%,7.83%～25.07%and 3.12%～19.31%with the combined applications of the three amendments.In the third season cabbage,the remediation efficiency of the combined applications of the three amendments reduced.With the evaluation index of Cd concentration in edible parts,the combination of“1%biochar+0.5%fly ash+1%white marble”and“1.5%biochar+1.5%fly ash+0.5%white marble”showed the greatest remediation efficiency.