Effect And Mechanism Of Different Passivating Agents On Mercury Activity In Farmland Soils Of Jilin Province

Due to the increasing frequency of industrial activities,the random disposal of garbage,the abuse of pesticides and chemical fertilizers,the mining and smelting of mines,the heavy metal pollution of farmland soil in China presents a serious trend.Mercury,a heavy metal,has high potential toxicity and is easy to accumulate through the food chain,which poses a serious threat to the ecological environment and human health.There is a potential risk of heavy metal pollution in cultivated soil of nickel mining area in Jilin Province.It is of great significance to explore the remediation methods of heavy metal pollution in farmland soil for preventing and controlling heavy metal pollution and ensuring the ecological security of farmland soil in Jilin Province.The existing remediation methods for heavy metal pollution in soils include physical,chemical,biological,and agronomic measures nowadays.Among them,the passivation remediation y is a method of repairing soil heavy metal pollution by adding a passivating agent to the contaminated soil,converting heavy metals from active to stable form and reducing the migration and bioavailability of heavy metals.In this paper,by sampling from the farmland soil in the nickel mining area of Jilin Province and simulating in the laboratory,the contents were studied as following: the passivation effect of eight kinds of passivating agents,including bentonite,phosphate rock powder,undisturbed palygorskite,modified palygorskite,sepiolite,volcanic slag,desulfurized gypsum,and organic fertilizer on exogenous mercury in the soil;the adsorption characteristics of mercury in five passivators,including volcanic slag,organic fertilizer,modified palygorskite,sepiolite and desulfurized gypsum being of significant passivation effect on the exogenous mercury;the effect of different amount of passivator on the speciation and distribution of mercury in the soil;the passivation mechanism of passivators on soil mercury according to the surface morphology and functional group characteristics of different passivators..The results of this study will provide scientific basis and technical support for the remediation of heavy metal pollution in farmland soil of Jilin Province.The results from the effects of different passivation agents on the activity of mercury showed that passivation effect of different passivation agents on the active mercury in the soil of Jilin Province was the order of modified palygorskite> volcanic slag > organic fertilizer > desulfurized gypsum >sepiolite> phosphate rock powder > bentonite > undisturbed palygorskite.According to the influence of different passivators on the content of water-soluble and exchangeable mercury,five passivators,including organic fertilizer,volcanic slag,sepiolite,desulfurized gypsum and modified palygorskite,were selected as passivators with remarkable passivation effect on the exogenous mercury in the soil.The results from the adsorption of mercury in different passivation agents showed that the adsorption kinetic characteristics of five passivators for mercury were described with Double constant rate equation and Elovich equation,and the adsorption thermodynamic characteristics were described by Freundlich equation.The order of adsorption rate for mercury was modified palygorskite> desulfurized gypsum>sepiolite> volcanic slag> organic fertilizer;adsorption capacity for mercury was the order of modified palygorskite>sepiolite> desulfurized gypsum> organic fertilizer> volcanic slag.The results from the effect of different adding amounts of passivator on the form distribution of mercury in soil showed that the percentage of inactive mercury in the total amount of soil mercury increased and the percentage of active mercury decreased with the increase of passivators.The results from SEM and FTIR showed that the passivators were generally porous and rough with large specific surface areas,and probably had Si-O-Al,Si-O,P-O or C-O bonds,as well as the active groups such as hydroxyl,amino,and carboxyl.Therefore,it can be inferred that the passivation mechanism for mercury in farmland soil from nickel mine in Jilin Province was as following: different passivators contain functional groups which can cooperate or chelate with mercury,the activity of soil mercury reduced due to the coordination or chelation of mercury when the passivator were added to the soil;the passivators have porous structure,rough surface and different specific surface area,which enhanced the adsorption of heavy metal mercury in the soil.In addition,the alkalinity of different passivators was beneficial to the hydrolysis of water-soluble mercury to produce the precipitate of oxide or hydroxide mercury,which can reduce the activity of mercury in the soil.