| Hg is a trace heavy metal with high environmental risk. The mercury levels in soil were several times higher than the background value of data in the early1980s in many areas, serious threat to human health and ecological safety. At present, many researchers tried to discuss the relationship with the mode of occurrence of soil Hg and the biological activity through analyze it. Humic acid is an important part of soil organic matter, which have a significant effect on soil Hg speciation and allocation of Hg in the soil solid phase and a liquid phase, through the ion exchange, adsorption, chelation and oxidation reduction reaction, because the heterogeneity of unique structure of humic acid contain a variety of groups with in high reaction activity. FA/HA is an important quantitative indicators to evaluation the humification of soil. Different FA/HA have a different structure and reactive. Its influence on the activity of soil mercury speciation will also differences. Hg in soil solution have a high activity, Hg content of the soil solution dominated by the soil solid phase Hg. In a state of dynamic equilibrium between the solid and liquid phases. Therefore, it’s very important to discuss the different conditions of humic acid to impact to Hg speciation distribution in the soil solid phase. So, this study used simulated experiment, discussed the humic acid to impact on distribution of Hg speciation in soil solid and solution at the different sources of humic acid, the different content of humic acid, the different FA/HA ratio and the Hg pollution levels. This study extracted and separated the different forms of soil solid phase, used Tessior sequential extraction method. Used the method of Bollen and Wenke extract the Hg in soil solution. Total Hg and speciation Hg of soil solution were measured. The results were as follows:The impact of humic acid on the morphology and activity of soil mercury were varies due to different types of humic acid and soils. Control of the concentration of soil Hg was lmg/kg, Added different sources of\%C humic acid(JY (It’s the soil humic acid that extracted Jinyun Mountain). TJ(It’s the Tianjin humic acid that extracted Lignite), SH(It’s the Shanghai humic acid that extracted Peat)) had significantly increased the content of organic combination Hg in three soils (yellow soil, purple tide soil and gray brown purple mud), which was the largest increased in yellow soil after added JY. The Hg on three soils were JY can increase the content of soil water soluble Hg in three soils, reduced the content of residual Hg. Compared to be blank, the water soluble Hg in purple soil increased most, increased by2.27%; the residual Hg in gray brown purple mud reduced most, reduced by5.83%. SH and TJ could strengthen the yellow soil, purple soil fixed on mercury, promoted the water soluble Hg to the low activity of the organic combination state, residual state Hg transformation, and the effect of SH was better than TJ. The residual Hg and organic combination Hg on purple tide soil increased most, compared to be blank, reduced by4.68%,4.48%respectively.The humic acid of different FA/HA ratio had a different effect on the transformation of soil mercury speciation.Under the same conditions of total carbon(1%C), the water soluble Hg of three soils increased gradually with the increase of the FA/HA ratio, and the residues and organic combination state mercury reduced gradually. For yellow soil and gray brown purple mud, Humic acid on the effect of soil Hg speciation marked a turning point when the FA/HA ratio was0.3. When the FA/HA≦0.3, humic acid could effectively inhibit the activity of soil mercury, promoted the water soluble, acid soluble Hg to the organic combination state, residual state Hg transformation,When the FA/HA was0, the decline of water soluble Hg on yellow soil was the largest, reduced by0.96%, the increase of residual state Hg was the largest, increased by3.18%. When the FA/HA>0.3, humic acid could enhance the activity of mercury in soil and promote the increase of water soluble Hg and the reduction of inert state Hg. When the FA/HA ratio was2, the decline of residual state Hg on gray brown purple mud was the largest, reduced by4.51%. As for the purple tide soil, humic acid on the effects of soil Hg speciation marked a turning point when the FA/HA ratio was0.7. When the FA/HA≦0.7, Humic acid could effectively inhibit the activity of soil mercury, the decline of water soluble Hg was the largest when the FA/HA ratio was2, reduced by1.36%.The increase of residual state Hg was the largest,increased by1.90%. When the FA/HA>0.7, humic acid could enhance the activity of mercury in soil, When the FA/HA ratio was2, the increase of water soluble Hg was the largest,increased by0.96%,and the decline of residual state Hg was the largest,reduced by2.60%.The influence of humic acid on the conversion of soil Hg speciation limited by the total carbon of humic acid. Different concentrations of humic acid had a significant effect on Hg speciation. When the FA/HA≦0.3, the greater the humic acid added amount, the more obvious effected on fixation of Hg from soils. When the FA/HA ratio was0and the adding of humic acid was2%C,the fixed effect was the best. The increase of residual state Hg were yellow soil(5.57%)> gray brown purple mud(3.52%)>purple tide soil (1.85%). When the FA/HA≧0.7, with the increase of the humic acid added amount, the water soluble Hg of three soils increased gradually and the residual state Hg reduced gradually. Activation of the mercury in the soil increased gradually. When the FA/HA ratio was2and the adding of humic acid was2%C, this activation were the most obvious, The increase of water soluble Hg were purple tide soil (4.60%)>yellow soil (4.33%)>gray brown purple mud (2.46%), The decline of residual state Hg were gray brown purple mud (5.42%)>yellow soil (2.07%)>purple tide soil (1.80%).The influence of humic acid on the conversion of soil Hg speciation closely related to the soil mercury pollution level. When the FA/HA ratio was same,with the increase of the adding of Hg, the alkali-soluble Hg on Three soils first increased then decreased, and the acid-soluble Hg contrast. When the FA/HA ratio was0.3, Hg concentrations was lmg/kg, humic acid had a better inhibitory effect on soil Hg, which could significant increase the content of the residual Hg in the soil. When the FA/HA≧0.7, water soluble mercury had increased to some extent in the three soils. When the FA/HA was2, the increase was the largest. The mercury concentration increased Omg/kg to3mg/kg, the water soluble Hg on yellow soil, purple tide soil and gray brown purple mud respectively increased1.46%,0.50%,0.57%.The humic acid of FA/HA ratio、the total carbon of humic acid and the soil mercury pollution level not only had a effect on the speciation distribution of the mercury on the soil solid phase. Throughout the aging process, acid soluble, alkali-soluble mercury change relatively gentle, Organic combination Hg increased considerably before aging15d and then decreased slightly, residual mercury showed an upward trend with aging time. When the FA/HA ratio was0, the adding of humic acid was1%C and the Hg concentrations was lmg/kg, the increase of residual mercury was the largest, increased by9.06%. Under the condition of different FA/HA ratio, Soil water soluble state mercury and exchange of mercury drops rapidly at the beginning of the aging then gradually tend to be stable. When the FA/HA ratio was1, the decrease was the largest, respectively reduced26.68%.9.56%. Under the condition of different the total carbon of humic acid and the soil mercury pollution level, Water soluble state mercury and exchange of mercury gradually reduced with the aging time. When the adding of humic acid was0.5%C and the Hg concentrations was lmg/kg, the decrease of water soluble state mercury was the largest, reduced by15.84%.The content and morphological changes of mercury in the soil liquid phase dominated by the soil solid phase. The mercury in solid phase could be activated by JY, at the same time which also could promote to increase the content of soil total Hg in liquid phase, the total Hg in purple soil increased most, increased by1.43μg/kg. SH and TJ passived the mercury in soil solid phase, while reduced the content of Hg in the soil liquid phase. Among them, the content of total Hg in the purple tide soil solution after adding TJ and in the gray brown purple mud solution after adding SH reduced the most, reduced by5.58,5.57μg/kg respectively. After adding three types humic acid, the distribution of various forms of Hg in the soil liquid phase(in addition to gray brown purple mud liquid adding JY) were organic active mercury>inorganic active mercury>elemental mercury. The content of organic active mercury was the biggest in yellow soil solution after adding JY, accounting for56.75%of the total mercury. The content of organic active mercury was the biggest in gray brown purple mud and purple tide soil solution after adding TJ, accounting for65.71%and65.71%of the total mercury respectively.With the increase of the FA/HA ratio, the total mercury in soil solid phase had been activated, the total mercury, organic active mercury, inorganic active mercury in soil liquid phase also gradually increased. The HA/FA ratio increased0to2, the total Hg and organic active mercury in gray brown purple mud liquid increased the biggest, reduced by17.55,15.66μg/kg respectively. When the FA/HA≦0.3, humic acid could effectively reduce the mercury content in soil solution, When the FA/HA ratio was0, the decline of the content of mercury in purple tide soil was the largest, the total Hg reduced by88.12%; When the FA/HA≧0.7, Humic acid could effectively increase the mercury content in soil solution, When the FA/HA ratio was2, the increase of the mercury content in gray brown purple mud was the largest, the total Hg、 organic active mercu、inorganic active mercury reduced by69.31%,46.58%,74.75%respectively.The mercury speciation changes of soil liquid was closely related with the content of humic acid total carbon and the concentrations of exogenous mercury in the soil solid phase. When the FA/HA ratio was0, with the increase of the the content of humic acid total carbon, the content of mercury decreased gradually in purple tide soil and yellow soil solution, which the purple tide soil decreased the biggest, the total Hg, organic active mercury, inorganic active mercury reduced by8.29,2.95,5.31μg/kg respectively. Compared to the blank, although the content of mercury in the gray brown purple mud liquid phase was significantly, but it increased slowly with increasing the carbon content of humic acid. When the FA/HA=0.3, activation of the mercury in the soil reduced effectively with increasing the carbon content of humic acid. When the FA/HA ratio was2and the adding of humic acid was2%C, the decrease of the mercury content in purple tide soil was the largest, the total Hg,organic active mercury,inorganic active mercury reduced by50.37,2.67,47.45μg/kg respectively. Under the condition of same HA/FA ratio, with increasing the concentration of exogenous mercury, total mercury and various forms of mercury levels significantly increased in three soil liquid phase.Under the condition of different HA/FA ratio and different sources of humic acid, the correlation analysis found that various forms of mercury in the soil solid and liquid phases had the high correlation. The content and morphological changes of mercury in the soil liquid phase dominated by the soil solid phase. Various forms of mercury in the liquid phase with water soluble, alkali-soluble mercury in solid phase were positively correlated, with the residual, acid soluble mercury was negatively correlated. Under the condition of different carbon contents of humic acid, various forms of mercury in the purple tide soil and gray brown purple mud liquid phase with water soluble, exchangeable, alkali-soluble mercury in solid phase were positively correlated, with the residual, acid soluble, organic combination state mercury was negatively correlated. Various forms of mercury in the yellow soil liquid phase with water soluble, exchangeable, acid soluble mercury in solid phase were positively correlated, with the residual, alkali-soluble, organic combination state mercury was negatively correlated.Under the condition of different soil types, different FA/HA, different content of humic acid, different concentration of mercury, Humic acid had a similarity effect on the dynamic transformation of mercury in the soil liquid phase. Total mercury and mercury species in the soil liquid phase decreased with the aging time. And also indirectly description the mercury in the soil liquid phase were fixed in the soil with the extension of the time, which transformed into mercury species of the less active, thereby reducing damage to the ecological environment. |
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