| The environmentalissues has long been a global concern as the society develops.The remediation of heavy metal pollution is one of the major tasks in our country.Stabilization of heavy metals,which has the advantage of fast repair rate,high efficiency,and“repair during productive process”model,has been a frequently-used and main remediation tool in current safety utilization of farmlands over national criteria.Siliceous amendment is commonly used in soil stabilization technology due to its good stability,good environmental compatibility,low costand abundant resources.Modification of minerals,whichmay alter their special surface properties and internal structure,has been widely used to enhance their remediation efficiency prior to their applications.This study intends to develop a new siliceous amendment to fix cadmium in soil by modifying molybdenum milltailings using necessary means.This is of great significance for heavy metal stabilization in farmlands and utilization of molybdenum milltailings.The main result of this study as follows:?1?In this study,field experiments were conducted to investigate the immobilization of cadmium by one marketable soil conditioner.The results indicated that this soil conditioner would slightly increase so il p H value and reduce the bio-availablity of cadmium in soils.However,the effects weren't significant.?2?Various modify methods,including ball-milling,acid modification,salt modification,alkali modification,were employed in this study to develop a new type of passivating agent based on molybdenum tailings.Then the modified molybdenum tailings were added into 100 mg·L-1 Cd solution to study their removal rate of Cd.The results indicated that the removal rates of Na-type and K-type amendments,which referenced from the method of artificial zeolite synthesis,were 99.76%and 98.64%,respectively.The removal rates of these two amendments have shown significant superior than the rest modified molybdenum tailing.?3?The thermodynamics and kinetics so rption experiments were introduced to study the mechanism of the Na-type and K-type amendments on adsorption of cadmium.The results indicated that the sorption of Cd by these two types of amendments matchs the Langmuir model andthe pseudo-second-order model perfectly.The results reveals that the adsorption of cadmium by these two amendments were mainly dominated by chemical adsorption processes,and were secondly dominated by electrostatic adsorption.The adsorption capacity of Cd by Na-type and K-type amendments were 158.73 mg·kg-1 and84.75 mg·kg-1,respectively.?4?The X-ray diffraction analysis?XRD?,specific surface area analysis?BET?,scanning electron microscopy-energy spectrum analysis?SEM-EDS?were conducted to explore the physical structures and surface properties of Na-type and K-type amendments.The results showed that the Na-type amendments has good mesoporous structures and typical crystalline structures,which fit the faujasite type structures and are considered good for cadmium adsorption.As for K-type amendments,ultra-small particle size and amorphousstructures.The EDS analysis illustrated the existence characteristic group of Cd after adsorption of these two amendments.The SEM analysis observed Cd polymeride on the surface of Na-type amendment after its sorption of Cd,while unconspicuous changes were obtained on the surface of K-type amendment t after its sorption of Cd.?5?Soil incubation experiments were conducted to study the application effects of these two amendments in three different types of soils under the dosage of 5%.The results indicated that the available Cd decreased significantly?>94%?after application of these two amendments.However,slight soil harden phenomenon was observed in some soils under this application amount.Then the effects of different additive amounts?0%,0.5%,1%,1.5%,2%?were studied.The results indicated that the immobilization rate increased along with the increase of the additive amounts.However,the increase trend became gentle after the 1%application.The immobilization rate of Cd by the Na-type and K-type amendments under 2%application were 96.20%and 83.53%,respectively.We can conclude that,from the obtained results,the best additive amount of these two amendments was 1%. |
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