| Mercury in the soil is absorbed by plants and accumulated in animals and humans through the food chain,which is harmful to human health,and this damage is not only related to the total amount of mercury accumulated in the soil,but also depends to a greater extent on mercury.Humic acid can change the morphology and bioavailability of mercury in soil due to its special structural characteristics.The mercury pollution in the soil of Wanshan area is serious.The application of humic acid alone may limit the fixation of mercury in the soil.Therefore,a combination of various passivating agents can be considered.Mesoporous silica ceramic nanomaterials(NA)have superior adsorption capacity for mercury,which can reduce the degree of mercury pollution in soil.In this paper,through the characterization of humic acid and nanomaterials,through laboratory experiments,chemical continuous extraction morphological classification method was used to investigate the occurrence of mercury in the mercury-containing soil of Wanshan with different concentrations of humic acid components fulvic acid and humic acid.At the same time,a pot experiment of humic acid and nanomaterials was carried out to illustrate the bioavailability of mercury in the soil,and the following results were obtained:1.Using Fourier transform infrared spectroscopy and scanning electron microscopy to study the main functional groups and surface structure of two humic acid samples FA and HA,it is found that FA contains more acidic groups,its carboxyl group,hydroxyl group,phenolic hydroxyl group and alcohol.The functional groups such as hydroxyl groups and ketone groups are more abundant than HA,while HA contains more amino groups,carbonyl groups and aliphatic groups.The functional characteristics of different functional groups of humic acid affect the possible mode of action with mercury.Referring to the structural characteristics of the FA and HA samples in the scanning electron microscope image,it was found that the FA was spherical and the surface was smooth and microporous;the HA was in a massive structure,and the surface was rough and pitted with obvious cracks.Different structural characteristics lead to differences in the possible modes of action of FA,HA and mercury:HA structural characteristics facilitate the diffusion of mercury ions into the interior of HA,the reaction process is not easy to desorb,and can form a stable complex with HA,while FA and mercury The main way of bonding may be that the functional groups on the surface of the FA adsorb mercury ions by electrostatic interaction.This bond is unstable and may desorb and re-release the mercury ions under certain conditions.2.The main functional groups and surface structure characteristics of NA were studied by Fourier transform infrared spectroscopy and scanning electron microscopy.The peaks of NA absorption peaks changed during the adsorption of mercury,and the absorption intensity of each absorption peak became stronger.NA surface Irregular mass characteristics are exhibited,and the adsorbed NA structure is broken and the specific surface area is increased.Referring to the structural characteristics of the NA sample in the SEM image,the possible mode of action of NA and mercury is illustrated:in the process of interaction between NA and mercury ions,NA is first combined with the mercury ion first adsorbed on the outer layer of NA,with the reaction time.The elongation and the reaction continue to occur,and the mercury ions gradually reach the interior of the NA,forming an inner layer complex with the NA in the form of a chemical bond/coordination covalent bond.The combination of mercury ions and NA releases more energy,and the original NA is The structure is broken,resulting in a crack in the structure of the NA combined with mercury ions,and a lot of micropores are newly formed,so that the specific surface area of the NA is increased.3.The effects of two active components of humic acid on the change of mercury form in soil showed that FA and HA could promote the conversion of water-soluble mercury,exchangeable mercury and acid-soluble mercury in soil to other forms,but the difference between the two components.The effect of concentration on mercury form is quite different.The soil water-soluble mercury and exchangeable mercury decreased by 6.28～7.05%and 13.25～15.89%in different concentrations of FA,respectively.The water-soluble mercury and exchangeable mercury decreased by 7.32 in 45 days under different concentrations of HA.7.46%and 14.26～16.7%.The alkali-soluble mercury and organic-bound mercury in the soils with FA and HA increased significantly.The alkali-soluble mercury and organic-bound mercury in the soil increased by 13.03～16.24%and 14.33～17.27%in different concentrations of FA,respectively.Under the action of HA,alkali-soluble mercury and organically bound mercury increased by 2.52～8.67%and 15.96～19.16%,respectively,in 45 days.Although different FA and HA concentrations have different effects on the transformation of soil mercury,the overall change of mercury form is consistent.The correlation analysis of humic acid on the change of mercury form in soil showed that the addition of humic acid changed the form of mercury in the soil,but the transformation between the various forms was not unidirectional,showing multiple forms.The dynamic balance of the conversion.4.In the plant pot experiment,the addition of FA,HA,NA,FA+NA,HA+NA can inhibit the activity of mercury in the soil and reduce the mercury content in plants.Different humic acid components have different fixation effects on mercury.Compared with FA,the fixation effect of HA on mercury is more obvious,and the combination of HA+NA has the greatest inhibitory effect on mercury activity in soil.After the whole plant pot experiment,the mercury content and morphological changes in the residual soil were affected by the added humic acid and nanomaterials.HA better reduced the content of water-soluble mercury and exchangeable mercury in the soil;FA could better reduce The content of acid soluble mercury in the soil.The content of alkali-soluble mercury and organically bound mercury in the soil with added HA was higher than that in the soil with dissolved FA and organically bound mercury.The residual mercury content in the soil of Chinese cabbage was higher than that in lettuce pot,and the mercury content in lettuce was higher than that in Chinese cabbage,whether it was root,stem or leaf or the whole plant,indicating that soil mercury was more effective against lettuce.5.The transport and enrichment ability of the two plants to soil mercury is different:in the pot experiment of Chinese cabbage,the transfer coefficient(TF)of FA and FA+NA is added to>1,and the TF<1 of HA,NA and HA+NA is added.The transport of mercury in the soil with added FA is stronger than that in HA,and the mercury added with HA and NA is transported less to the ground.In the pot experiment of lettuce,adding TF>1 of FA,HA and FA+NA,the transport ability of mercury in lettuce was stronger,indicating that the plant activity of mercury on lettuce was higher.Both Chinese cabbage and lettuce are not enriched plants of mercury.In different treatments,the enrichment ability of Chinese cabbage and lettuce is different.In the potted cabbage,the addition of FA in Chinese cabbage has the highest mercury enrichment ability(0.476).HA+NA pakchoi had the lowest mercury enrichment ability(0.009);in lettuce potted plants,the addition of FA in lettuce increased the maximum mercury enrichment(0.439),and the addition of HA+NA lettuce had the lowest mercury enrichment ability(0.117). |
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