مطالعه ريزساختاري و تغييرات نفوذپذيري خاك هاي رسي در حضور كودهاي فسفاته

Microstructural Study and Permeability Variations of Clayey Soils at the Presence of Phosphate Fertilizers

ﻧﻴﺎز ﺑﻪ ﺗﻮﻟﻴﺪ ﺑﻴﺸﺘﺮ ﻣﺤﺼﻮﻻت ﻛﺸﺎورزي در واﺣﺪ ﺳﻄﺢ ﻣﻮﺟﺐ اﻓﺰاﻳﺶ اﺳﺘﻔﺎده از ﻛﻮدﻫﺎي ﺷﻴﻤﻴﺎﻳﻲ و ﺳﺎﻳﺮ ﻋﻮاﻣﻞ ﺧﻄﺮزا ﺑﺮاي ﻣﺤﻴﻂ زﻳﺴﺖ ﺷﺪه اﺳﺖ. از ﺳﻮي دﻳﮕﺮ اﺳﺘﻔﺎده از ﻛﻮدﻫﺎي ﺷﻴﻤﻴﺎﻳﻲ ﻣﻮﺟﺐ ﺗﻐﻴﻴﺮ ﺳﺎﺧﺘﺎر و وﻳﮋﮔﻲﻫﺎي ژﺋﻮﺗﻜﻨﻴﻜﻲ ﺧﺎك ﻣﻲﺷﻮد و اﻳﻦ اﻣﺮ ﻣﻲﺗﻮاﻧﺪ در اﻓﺰاﻳﺶ آﻟﻮدﮔﻲﻫﺎي ﺳﻄﺤﻲ و زﻳﺮزﻣﻴﻨﻲ ﻣﻮﺛﺮ ﺑﺎﺷﺪ. ﺑﺮ اﻳﻦ اﺳﺎس ﻫﺪف اﻳﻦ ﭘﮋوﻫﺶ ﻣﻄﺎﻟﻌﻪ ﺗﻐﻴﻴﺮات ﻧﻔﻮذﭘﺬﻳﺮي و ﺗﻐﻴﻴﺮات ﺳﺎﺧﺘﺎر و رﻳﺨﺖﺷﻨﺎﺳﻲ ﺧﺎكﻫﺎي رﺳﻲ در اﻧﺪرﻛﻨﺶ ﺑﺎ ﻛﻮدﻫﺎي ﺷﻴﻤﻴﺎﻳﻲ ﻓﺴﻔﺎﺗﻪ اﺳﺖ. در اﻳﻦ راﺳﺘﺎ ﺑﺎ اﻧﺠﺎم ﻳﻜﺴﺮي آزﻣﺎﻳﺶﻫﺎي ژﺋﻮﺗﻜﻨﻴﻜﻲ و ژﺋﻮﺗﻜﻨﻴﻚ زﻳﺴﺖﻣﺤﻴﻄﻲ، ﻓﺮاﻳﻨﺪ اﻧﺪرﻛﻨﺶ ﻧﻤﻮﻧﻪ رﺳﻲ ﺑﻨﺘﻮﻧﻴﺖ ﺑﺎ ﻛﻮدﻫﺎي ﺷﻴﻤﻴﺎﻳﻲ ﻓﺴﻔﺎﺗﻪ ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ. ﺑﺮرﺳﻲ ﺗﻐﻴﻴﺮات ﺿﺮﻳﺐ ﻧﻔﻮذﭘﺬﻳﺮي، رﺳﻮب، وﻳﮋﮔﻲﻫﺎي ﺧﻤﻴﺮي ﺧﺎك، ﺗﻐﻴﻴﺮات pH ﻣﺤﻴﻂ، ﻧﺘﺎﻳﺞ رﻳﺰﺳﺎﺧﺘﺎري ﭘﺮاش اﺷﻌﻪ اﻳﻜﺲ )XRD( و ﺗﺼﺎوﻳﺮ ﻣﻴﻜﺮوﺳﻜﻮپ اﻟﻜﺘﺮوﻧﻲ ﭘﻮﻳﺸﻲ )SEM( ﻧﺸﺎن ﻣﻲدﻫﺪ ﻛﻪ ﺣﻀﻮر ﻛﻮدﻫﺎي ﻓﺴﻔﺎﺗﻪ ﻣﻮﺟﺐ ﺗﻐﻴﻴﺮ ﺳﺎﺧﺘﺎر ﺧﺎك رﺳﻲ ﺷﺪه اﺳﺖ. ﺑﺮ اﺳﺎس ﻧﺘﺎﻳﺞ اﻳﻦ ﭘﮋوﻫﺶ ﭼﮕﻮﻧﮕﻲ ﻗﺮارﮔﻴﺮي ﺳﺎﺧﺘﺎر و اﺑﻌﺎد ﺻﻔﺤﺎت رﺳﻲ ﺑﻪ ﺷﺪت ﺗﺤﺖ ﺗﺄﺛﻴﺮ ﻣﻴﺰان ﻛﻮدﻫﺎي ﻓﺴﻔﺎﺗﻪ اﺳﺖ. ﻫﻤﭽﻨﻴﻦ ﺣﻀﻮر ﻛﻮدﻫﺎي ﻓﺴﻔﺎﺗﻪ ﻣﻮﺟﺐ ﻛﺎﻫﺶ ﺷﺪت ﻗﻠﻪ اﺻﻠﻲ ﻛﺎﻧﻲ رﺳﻲ ﻣﻮﻧﺖﻣﻮرﻳﻠﻮﻧﻴﺖ و اﻓﺰاﻳﺶ ﺿﺮﻳﺐ ﻧﻔﻮذﭘﺬﻳﺮي ﺧﺎك ﻣﻲﺷﻮد ﺑﻪ ﻧﺤﻮي ﻛﻪ اﻓﺰاﻳﺶ ﺣﺪود 0/5 %ﺳﻮﭘﺮﻓﺴﻔﺎت ﺗﺮﻳﭙﻞ ﺣﺪ رواﻧﻲ ﻧﻤﻮﻧﻪ ﺑﻨﺘﻮﻧﻴﺖ را 27% ﻛﺎﻫﺶ داده و ﺳﺒﺐ اﻓﺰاﻳﺶ ﺿﺮﻳﺐ ﻧﻔﻮذﭘﺬﻳﺮي ﺧﺎك ﺑﻪ ﻣﻴﺰان ﺣﺪود 100 ﺑﺮاﺑﺮ ﺷﺪه اﺳﺖ.

In the recent years the use of phosphate fertilizer has been increased. On the other hand, the use of phosphate fertilizer causes change in micro-structure and geotechnical properties of clayey soils. This may raise the risk for groundwater contamination. The main objective of this paper is to study the permeability and microstructural change of clayey soils after interaction with phosphate fertilizer. To achieve the above mentioned objective, series of geo-environmental engineering experiments was performed and the process of interaction of bentonite with phosphate fertilizer is studied. The evaluation of permeability variations, sedimentation tests, plasticity properties, soil pH variations and results of XRD and SEM experiments show that the presence of phosphate fertilizer changes the clay soil microstructure. Based on the results of this study phosphate fertilizer causes a reduction on the quantity of intensity of basal spacing of montmorillonite. Consequently the permeability might increases around1000 times at the presence of 10 percent phosphate fertilizer.