| In this research, sand and two soils(B horizon of yellow brown soil in Xiaogan city and brown red soil in Wuhan City, Hubei Province) were collected as experimental material. Added different of leaching solution of iron-manganese, pumped in an air which was simulated the alternating wet and dry process by air pumping, a process of alternating wet and dry was a cycle. Leach ten cycles as a stage in sand column and twenty cycles in soil column. Samples were collected at the end of each stage and some analyses were carried out such as pH and iron,manganese contents of the leachate, iron-manganese oxides of different forms in soils and sand cutans, the contents of iron-manganese oxides extracted by HAHC in iron-manganese cutans, and the surface topography of cutans was observed by SEM to study the formation mechanism of iron-manganese cutans. conclusions are as follows:1.According to the content of Fe-Mn in the leaching solution, which indicated the development conditions of cutans in the sand columns and soil column. The changing of Fe-Mn in the leaching solution was 1)Different stages, the content of Fe in the leaching solution was lower than leaching, the content of Mn in the leaching solution was bigger than leaching, showing the cutans adsorption of Fe2+ was higher;2)The content of Fe2+ in the leaching solution in the simulation of iron cutans was lower than simulation of iron-manganese cutans,description Mn ions in the leaching may play a role of competition on the adsorption of Fe2+ in the cutans, which reduced to adsorption of Fe2+ 3)The content of Fe in the leaching was higher concentrations, the higher of Mn was played a catalytic role in the concentrations adsorption of Fe2+ by cutans, but the other the higher of Mn was played a competition role in the concentrations adsorption of Fe2+ by cutans;4)If the leaching containing a certain of Fe2+, which can promote the absorption of Mn in the film. The content of Mn in the leaching was higher concentrations, the higher of Fe was played a catalytic role in the concentrations adsorption of Mn2+ by cutans, but the other, the higher of Fe was played a competition role in the concentrations adsorption of Mn2+ by cutans;5)Solution the process of cutans, the adsorption of Mn2+ in the yellow-brown soil was higher than the red-brown, the texture of yellow brown soil is clay and the texture of brown-red soil was silty clay loam, which indicated that Mn2+ more easily oxidation.deposition in the yellow-brown.2. The changing of leaching pH, which could indirectly explain the changing of cutans in the sand columns and in the soil column. The changing of leaching pH indicated:the leachate pH of CK2 and CK3 higher than 5 in the iron simulation cutans, but the others are lower than 5, the concentration of manganese in the leaching increased may further promote leaching pH lower. the changing of leachate pH in CK3,C,D was above.In the previous, the leaching solution pH in soil decline sharp, which may be related to adsorption of more Fe2+ or Mn2+ in the previous, the formation of oxides deposited adsorbed OH- release more H+, thus contributing to the leaching solution pH of soil decreased. If the adsorption content of Fe-Mn decreases in the soil, the changing of leaching solution pH was slowly decreasing. After five leaching, leaching solution pH of brown-red soil was lower than yellow-brown,which may be related to the content of pH and CEC in the soil.3. The different forms content of iron oxide is higher than manganese oxide in the cutans. The results 1) the concentration of iron is from 0.02mol/L increased to 0.04mol/ L in the leaching, the free state content of Fe showed an increasing trend in the cutans, which indicated that a higher concentration of iron may help iron oxide formation in cutans.2) If the concentration of Fe was 0.04mol/L in the Fe-Mn leaching, with the concentration of manganese increased in the leaching, the free state content of Mn showed an increasing trend in sand cutans. If the concentration of Fe was 0.02mol/L in the Fe-Mn leaching, with the concentration of manganese increased in the leaching, the free state content of Mn If the concentration of Fe was 0.04mol/L in the Fe-Mn leaching, with the concentration of manganese increased in the leaching, the free state content of Mn was no significant difference in sand cutans. If containing a high concentration of iron in the leaching, which conducived to the formation of manganese oxide in the cutans.3) The free state contents of Fe in the iron-cutans were higher than iron-manganese cutans, and the free state contents of Mn in the iron-manganese cutans were higher than iron cutans on different of stage. The ratio of the free state content of iron-manganese oxide was less than 0.1, which indicated that free state content of iron oxide was bigger than manganese in the cutans.4) The activation of Fe-Mn in the bottom of the sand columnwas less than in the upper and middle, which related to the environment of sang cutans. The alternating wet and dry was obvious in the upper and middle column which was benefit for activation of Fe-Mn oxide; but if the bottom of sand column was wet in a long period, which promoted the aging of iron-manganese oxides.5)the extraction content of manganese was only 9.95% -35.12% by HAHC, suggesting that the manganese oxide may be wrapped by iron oxide on the cutans.6)Leaching after twenty times in the soil, the whole content of Fe-Mn changing was more significant. Based on the determination of the free state of Fe-Mn in the cutans, the iron oxidation maybe played a catalytic role for adsorption of Mn2+ at pH 5 conditions,7) Leaching after twenty times in the soil, the amorphous content of iron-manganese and the complex content of iron-manganese increased significantly, which showed an increase or even a hundred times compared with non-leached soil. The activation grade of Fe-Mn in the brown-red soil and yellow brown increased obvious which increased 18.72%-34.92%21.51% -41.04% compared with non-leaching.4. The redox reactions was frequent when the alternating wet and dry changes in the upper obvious sand column, and the others have a strong reduction in a humid environment which may be have different effects on the morphology of cutans. From the second phase to the fifth stage, the transformation of the cutans have different morphologies in the sand column. A little of the plate structure have transformation to a large area of lath structure or similar needle-like structure in the middle and upper sand column; the lath structure or similar needle-like structure have transformation to globular structure or plate in the lower of column. The alternating of wet and dry maybe have promote to the structure transformation of lath or similar needle-like; and humid environment maybe have promote to the transformation of the spherical structures and the plate structure. 5. As for the mass percentage of iron in the column CK at different stages, the middle layer was higher than the upper and under layers. The mass percentage of iron-manganese in the column E trended to increase. Both for CK and E micro-part at different stages and different layers, there was more iron and iron-manganese oxides in the ball and layer structure. |
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