The Characteristics Of Iron And Manganese Migration And Deposition In Quartz Sand And The Brown-Red Soil Columns

In this study, the quartz sands and the brown-red soils with little iron-manganese were collected as materials for test, single or mixed iron-manganese solution (FeSO4O-0.08mol/L, MnCl20-0.08mol/L) were used to leach quartz sand columns and soil columns simultaneously or alternately(substituted every ten times), in which quartz sand and brown-red soil were leached ten times and twenty for a sample stage. In addition, different solution pH(sand columns at pH5and pH3.5, soil columns at pH3.5) and molar ratios (Fe/Mn was1:1,2:1,4:1) were setted in leaching treatments. We analysed the change of the leachate from the columns and the conditions of iron and manganese migration and deposition in the columns, to investigate the characteristics affected the iron and manganese leaching in soils. The results were as follows:1. With the increase in numbers of leaching, in the quartz sand columns, pH of leachate in each treatment fluctuated. The pH of leachate at pH5decreased fluctuatly,while they were steady at pH3.5. The leachate pH of sand columns which were leached with mixed iron-manganese solution changed slightly, ranged in3.0-4.5and2.4-3.5respectively at pH5and pH3.5. However, The leachate pH of sand columns which were leached with iron or manganese solution alternately varied obviously, especially that of pH5columns were periodic changing.The D-value at different stage could reach1.5. Compare with quartz sand columns, the pH of soil columns’leachate had the same change trend, they all decreased to about2.5.2. The concentration of iron and manganese in leachate were related to the leaching way and stage. There was little variation in that of sand columns leached with mixed iron-manganese solution, approaching the original solution. Otherwise, they were changed with the leaching period in the sand columns leached by single iron or manganese solution alternately. When leached iron solutions, the iron concentration closed to the original solutions’, while the manganese concentration were low and it dropped to0quickly, and vice versa. The concentration of iron and manganese from soil columns changed slowly through the process, and had the same trend with sand columns. The concentration from soil columns leached with iron or manganese solution alternately changed when period altered, finally closed to the origin. 3. With the leaching progress, the iron and manganese contents increased, the former was more than the the latter. There were more and more iron and manganese deposited on the sands when leached simultaneously, howere, the quantity of iron and manganese on the sands in the columns leached alternately become up and down when the stage alternated. The contents of iron and manganese in sands columns at pH3.5(high iron and manganese concentration) were more than that at pH5(low iron and manganese concentration). There were more in the under layers(15cm) than upper(5cm) and middle(15cm) layers at pH3.5, but there was no similar phenomenon at pH5. When molar ratios were2:1and4:1, the illuviation of iron was more, and the manganese illuviation was more when the original manganese concentration was high. The iron-manganese oxides formed in the early time of leaching promoted the illuviation of the oxides in the latter period.4. The SEM micrographs and EDS scan patterns shows:the distributions of iron and manganese on the sands were not uniformity and the illuviation of iron was more than manganese. The iron and manganese materials distributed intensively, clustered as small slices, spheres and bulks shapes. And materials deposited dispersely on sands leached alternately as wee slices. With the increase in the number of leaching, the contents of iron and manganese on quartz sand increased gradually, higher concentration treatments had more illuviation.5. With a long time leaching, the pH and Eh of the soil came down. The pH in soil columns leached simultaneously were lower than those in columns leached alternately. While the Eh of soil in different treatments were near, the soil were all at deoxidation condition. The basic ions in the soil especially calcium and magnesium were washed away fiercely, while leaching proceed.6. In the soil columns,there was more iron deposition than manganese, but both of them are higher than in the quartz sand column. The contents of free iron-manganese in quartz sands were the highest, and they could reached91.67mg/g and4.64mg/g respectively. The next were amorphous iron-manganese contents increased gradually, they could reached71.49mg/g and4.47mg/grespectively. The least were bonded state, they were below7mg/g. The full amount, free and amorphous state of iron were several or dozens times moer than those of manganese. The bonded state iron and manganese contents were close. The iron contents of all state increased with the leaching proceding, otherwise, the manganese phenomenon was the opposite. In the soil columns leached simultaneously, the illuviations of iron were more than those in columns leached alternately, the depositions of manganese were on the congtrary.