Effect of interaction between organic and mineral colloids in the quantity of negative and positive charges of clay minerals

Abstract

    This study was conducted to identify the proportion of the contribution of mineral and organic soil components in the values of Cation exchange capacity in some soils with high organic content and compare them with soils with low organic content. To achieve this goal, seven sites were selected for each surface and subsurface sample. Selected  sites included Al-Dalmach marsh in Wasit governorate and the marshes soils in Misan governorate included(Al-Azim, Al-sanaf ,Um Naaj and Al-Sudda), as well as one soil site in Diwaniyah governorate, samples of surface and subsurface from all above mentioned sites were collected, dried, grinded and sevied through2mm opening sieve, and placed in plastic cans to store in lab.(Physical, Chemical and Mineralogical ) properties  were analyzed in the laboratories of the Faculty of Agriculture, Wasit University, except for the X-ray diffraction tests of the clay fraction, was conducted in the laboratories of the Ministry of Science and Technology/  Baghdad and the scanning electron microscope (SEM) were done at the Faculty of Sciences / University of Kufa.

     The X-ray diffraction results showed the presence of a group of clay minerals exhibited by a group of different peaks at different intensities, most notably the presence of smectite minerals in the range of 14 Angstrom as well as chlorite minerals in the same peak, which can be distinguished from smectite by its remaining in 550Cᵒ heating treatment as well as the second 7 Angestrom , also the results showed existance of  Mica-Smectite as well as Mica-Chlorite regular interstratified    minerals, The presence of the mica group was observed through its well-known 10-angstrom peak, which appeared with different intensities, sometimes slightly higher than this value, and sometimes slightly decreased, depending on the weathering status to which this mineral is exposed, as evidenced by the appearance of peak of the regular interstratified minerals mica-smectite as well as mica-chlorite, the data revealed Kaolinite mineral from 7 Angstrom peak which can be distinguished from the second 7 of the chlorite minerals through its breakdown and disappearance in the treatment of heating at 550 Cᵒ.

     Images of the scanning electron microscopy of selected samples from the study's soil sites showed the appearance of clay minerals as a function of weathering at different intensity affecting the morphology of minerals and the emergence of a series of changes in the edges and layers zones that gave clear evidence of the impact on the wet conditions of the soils resulting oxidation and reductions conditions  that affect the shape and structure of the mineral through the emergence of the process. An important manifestation of the scanning electron microscope is the state of overlap between the organic matter and the clay fraction, which appeared in the non-removable samples of the organic matter and formed by organic molecules of coverings around the particles of clay minerals. This situation has an effect on the exchange properties of both organic and mineral fractions, the images show the appearance of some living skeletens within theseparticles.
The cation exchange capacity of the study's samples ranged from 19-57 Cmol.kg^-1 where Alsudda marsh soil in its subsurface depth recorded the highest value of the Cation Exchange Capacity while the lowest value of the Cation Exchange Capacity in the Diwanyah soil in its second depth and it is also noted through the values referred to that there is a state of variation between the studied sites on the one hand and the two depth of each site on the other hand. This variation is due to the difference between the sites in the total quantity of organic matter as well as the difference in the proportions of their fractions (Humic, Volvic and Humin) on the other hand.

     The CEC values for the organic part ranged from (4-46) Cmol.kg^-1 where the highest value was recorded in Alsudda marsh soil in the subsurface depth while the lowest value was recorded in Diwanyah soil in the subsurface depth as well, In the light of these values, the apparent variation in the values of cation exchange capacity can be observed both between sites and between the two studied depths. This variation relied mainly on the proportion of total organic matter on the one hand and the proportions of organic matter fractions (humic acid, volfic acid and humin) on the other.

     Cation exchange capacity values for study soil samples removed from organic matter varied (representing the exchange capacity of the clay mineral fraction only) between (7-16) Cmol.kg^-1 The highest value was recorded in the Diwaniyah soil and the lowest was recorded in the Um naaj marsh soil. The above results indicated, variation in the CEC values can be observed between the sites on the one hand and the two studied depths on the other hand.