Immobilization Of Cadmium In Acid Soil By Oyster Shell Powder

Soil acidification and cadmium?Cd?contamination in agriculture soils are of increasing concern,due to the high risk of Cd in acid soil on human health through food chain.It is well recognized that the activity of Cd depends mainly on its various chemical species.The species of Cd can be changed and its activity can be immobilized by adding amendments.Therefore,the purposes of the dissertation are about the effects of oyster shell powder on the remediation of acid soil coupled with Cd contamination,and an amendment compound based on oyster shell powder is prepared.Moreover,this immobilization mechanism of Cd is discussed.The dissertation contains four chapters.Chapter one,soil acidification and Cd contamination in agricultural soils were introduced based on reading a lot of literatures.Techniques concerning remediation of Cd were also summarized.The emphasis that the application of oyster shell powder on the immobilization of heavy metal were expounded.Chapter two:the effects of oyster shell powder on the species distribution of Cd in acid soil were investigated.Results showed that when adding 50 g/kg_?soil?of oyster shell powder?150mesh?and incubating with soil for 30 days,the content of Cd species,such as in the fractions of acid soluble,reducible and oxidable forms,reduced significantly by 12.92%²0.97%,18.99%³1.10%and 18.02%³1.10%,respectively,and residual forms increased by 124.2%¹24.2%.It could be concluded that acid soluble,reducible and oxidable forms might convert into those in the residual forms after adding soil with the oyster shell powder.Chapter three:a compound amendment of oyster shell powder was prepared.Orthogonal experiment results showed that when the compound amendment with optimum ratio of 50 g/kg_?soil?oyster shell powder,15 g/kg_?soil?hydroxyapatite and 20 g/kg_?soil?biochar could dramaticlly reduce the content of active Cd by 76.1%in 15 days,and achieve stability in 30 days.Chapter four:the pot experiments were carried out to study the mobility and bioavailability of Cd using the compound amendment,and the influence for Cd and Ca uptake by plant was researched.Furthermore,the immobilization mechanism of Cd in soil was analyzed by XRD.The results showed that the content of Cd species in vegetable-soils,such as in the fractions of acid soluble and reducible forms decreased significantly by 32.2%⁵0.1%and 13.4%³7.9%,respectively.At the same time,oxidable forms increased slightly by 3.29%³3.6%,and residual forms did not change obviously.Amendments could effectively inhibit the Cd uptake by mustard edible part,compared with the control group,the compound amendment reached the inhibition rate of 97.1%,while oyster shell powder having the inhibition rate of 65.7%,coming to a conclusion that the compound amendment was more effective at immobilizing biological activity of Cd in soil.In addition,the compound amendment could increase the content of Ca of mustard edible part,6.78 times higher than the control group.The result of XRD showed that the main function of Cd immobilization was the formation of the precipitate of Cd?OH?₂ and CdCO₃.