Effect Of Hematite On HAP Immobilization Of Copper And Cadmium Under Flooding Conditions

The area of southern paddy soil contaminated by heavy metals is gradually expanding.Because the southern paddy soil is rich in a large amount of iron oxides,especially hematite,it will interact with the currently widely used phosphoruscontaining repair materials,thus affecting the repair effect on contaminated soil.Therefore,four treatment groups(control,hematite,hydroxyapatite(HAP),hematite mixed hydroxyapatite)were designed to treat paddy soil contaminated by heavy metals Cu and Cd under flooding culture.The hematite treatment group and the mixed additive treatment group were simultaneously set with three groups of hematite addition amounts of 1%,3% and 5%.Using Visual MINTEQ software to evaluate the formation and migration of heavy metal pollutants in the soil during cultivation and evaluate the repairing effect thro?gh wheat culture experiment.The changes of heavy metals,iron and phosphorus in the soil were determined by chemical analysis.The results are as follows:(1)Three groups of experimental treatments can reduce the content of Cu and Cd in soil pore solution.The mixed additive has the best treatment effect,can effectively reduce its P content and reduce the risk of eutrophication.(2)Correlation analysis showed that the activity of Cu and Cd in soil pore water was mainly controlled by soil pH;Visual MINTEQ model calculation showed that the ion activity of Cu and Cd was not related to any precipitation.The combination of the two shows that the fixation mechanism of soil heavy metals Cu and Cd may be surface adsorption.(3)The addition of HAP can greatly reduce the content of the most active ion exchange state Cu and Cd in the soil,and transform it into moderately active state and stable state,thus reducing soil the activity of Cu and Cd.The addition of hematite can reduce the activity of Cu,but the effect on Cd is not obvious.Moreover,with the increase of the proportion of hematite,the content of free iron oxide and crystalline iron oxide in the soil also increased gradually,but the content of amorphous iron oxide did not change significantly.At the same time,the addition of hematite can reduce the content of active phosphorus in the soil and transform the soil P into a stable state.(4)The wheat culture experiment shows:The germination rate of wheat in the HAP treatment group was the highest(100%),and the inhibition rate of wheat root elongation in the mixed additive treatment group was the lowest(64.01%).The concentration of Cu and Cd in wheat plants treated by four treatments are as follows: blank>hematite treatment>HAP treatment>mixing additive treatment,and the higher addition of hematite,the lower Cu and Cd concentration in wheat plants.Figure[20] Table[13] Reference[97]...