انتقال نانوذرات TiO2 در ستون هاي خاك دست نخورده: تاثير نرخ جريان

Transfer of TiO2 Nanoparticles in Undisturbed Soil Columns: Effect of Flow Rate

ﺑﺮاي ﺑﺮرﺳﯽ اﻧﺘﻘﺎل ﻧﺎﻧﻮذرات در ﻣﺤﯿﻂ ﻣﺘﺨﻠﺨﻞ، ﺑﺎ ﺗﻮﺟﻪ ﺑﻪ ﻣﺤﺪودﯾﺖ اﺑﺰارﻫﺎي آزﻣﺎﯾﺸﮕﺎﻫﯽ و دﺷﻮار ﺑﻮدن ﺗﻔﺴﯿﺮ ﻧﺘﺎﯾﺞ ﺑﻪدﺳﺖ آﻣﺪه در ﻣﺤﯿﻂﻫﺎي ﻣﺘﺨﻠﺨﻞ ﭘﯿﭽﯿﺪه ﻣﺎﻧﻨﺪ ﺧﺎك، اﻏﻠﺐ از ﻣﺤﯿﻂﻫﺎي ﻣﺘﺨﻠﺨﻞ، ﻫﻤﺎﻧﻨﺪ داﻧﻪﻫﺎي ﺷﯿﺸﻪاي، ﺷﻦ، داﻧﻪﻫﺎي ﺧﺎﻟﺺ ﮐﻮارﺗﺰ و ﺷﻦﻫﺎي ﺑﺴﺘﺮ رودﺧﺎﻧﻪ اﺳﺘﻔﺎده ﻣﯽ ﺷﻮد. در اﯾﻦ ﺗﺤﻘﯿﻖ، اﺛﺮ دﺑﯽﻫﺎي ﻣﺨﺘﻠﻒ ﺟﺮﯾﺎن ﺑﺮ اﻧﺘﻘﺎل ﻧﺎﻧﻮذرات دي اﮐﺴﯿﺪ ﺗﯿﺘﺎﻧﯿﻢ در ﺳﺘﻮنﻫﺎي ﺧﺎك دﺳﺖﻧﺨﻮرده ﺑﺮرﺳﯽ ﺷﺪ. دﺑﯽ در واﺣﺪ ﺳﻄﺢ ﺑﺮاﺑﺮ ﺑﺎ ﻫﺪاﯾﺖ ﻫﯿﺪروﻟﯿﮑﯽ اﺷﺒﺎع )ﺟﺮﯾﺎن اﺷﺒﺎع(، 0/7 ،0/9 و 0/5 ﺑﺮاﺑﺮ ﻫﺪاﯾﺖ ﻫﯿﺪروﻟﯿﮑﯽ اﺷﺒﺎع ﺧﺎك )ﺟﺮﯾﺎن ﻏﯿﺮاﺷﺒﺎع( ﺗﻮﺳﻂ ﭘﻤﭗ ﭘﺮﯾﺴﺘﺎﻟﺘﯿﮏ )BT100-1F( ﺑﻪ ﺳﺘﻮنﻫﺎي ﺧﺎك اﺿﺎﻓﻪ ﺷﺪ. ﺑﺎ اﻧﺪازهﮔﯿﺮي ﻣﻨﺤﻨﯽﻫﺎي رﺧﻨﻪ ﻣﺮﺑﻮط ﺑﻪ ﻫﺮ ﺳﺘﻮن، ﭘﺎراﻣﺘﺮﻫﺎي ﺗﺒﯿﯿﻦ ﮐﻨﻨﺪه اﻧﺘﻘﺎل ﻧﺎﻧﻮذرات ﺑﺮ ﻣﺒﻨﺎي ﻣﺪل ﺟﺬب ﺗﮏ ﻣﮑﺎﻧﯽ، ﻣﺪل ﺟﺬب ﺳﯿﻨﺘﯿﮏ ﺗﮏ ﻣﮑﺎﻧﯽ و ﻣﺪل ﺟﺬب ﺳﯿﻨﺘﯿﮏ دو ﻣﮑﺎﻧﯽ ﺗﻌﯿﯿﻦ ﺷﺪﻧﺪ. ﻧﺘﺎﯾﺞ ﺣﺎﮐﯽ از آن اﺳﺖ ﮐﻪ ﺑﺎ اﻓﺰاﯾﺶ ﻧﺮخ ﺟﺮﯾﺎن، ﻏﻠﻈﺖ ﻧﺴﺒﯽ ﻧﺎﻧﻮذرات TiO2 )ﻏﻠﻈﺖ ﻧﺎﻧﻮذرات در ﺧﺮوﺟﯽ ﺳﺘﻮنﻫﺎي ﺧﺎك ﻧﺴﺒﺖ ﺑﻪ ورودي آن( از 3 درﺻﺪ ﺑﻪ 28 درﺻﺪ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ. در ﺑﯿﻦ ﻣﺪلﻫﺎي ﻣﻮرد ﺑﺮرﺳﯽ، ﻣﺪل ﺟﺬب ﺳﯿﻨﺘﯿﮏ دو ﻣﮑﺎﻧﯽ ﻋﻼوه ﺑﺮ ﻟﺤﺎظ ﻧﻤﻮدن ﻣﮑﺎﻧﯿﺴﻢ ﺣﺒﺲ ﻓﯿﺰﯾﮑﯽ ﮐﻪ ﺑﺮاﺳﺎس اﻧﺪازه ذرات و ﻣﻨﺎﻓﺬ ﻣﺤﯿﻂ ﻣﺘﺨﻠﺨﻞ ﺻﻮرت ﻣﯽﮔﯿﺮد، ﺑﺎ وارد ﮐﺮدن ﺗﺎﺑﻊ اﺷﺒﺎع ﺷﺪن ﺳﻄﺢ ذرات ﻣﺤﯿﻂ ﻣﺘﺨﻠﺨﻞ ﺑﺎ ﻧﺎﻧﻮذرات و ﺗﺎﺑﻊ ﺣﺒﺲ ﻓﯿﺰﯾﮑﯽ ﮐﻪ ﺗﻐﯿﯿﺮات اﯾﻦ ﻣﮑﺎﻧﯿﺴﻢ ﺑﺎ ﻓﺎﺻﻠﻪ را ﻟﺤﺎظ ﻣﯽﮐﻨﺪ، ﺑﻬﺘﺮﯾﻦ ﺑﺮازش )90 %>R2( را در ﺑﯿﻦ ﺳﻪ ﻣﺪل ﺑﻪ ﮐﺎر ﮔﺮﻓﺘﻪ ﺷﺪه ﺑﺮاي ﺗﺨﻤﯿﻦ ﻣﯿﺰان اﻧﺘﻘﺎل ﻧﺎﻧﻮذرات از ﺳﺘﻮن ﺧﺎك ﻧﺸﺎن ﻣﯽدﻫﺪ.

Due to limitations of laboratory tools and difficulty in interpreting the results obtained from complex porous media such as soil, artificial porous media such as glass beads, pure sand and quartz and riverbed sand are oftenly used to investigate the transfer of nanoparticles in porous media. In this study, the effect of different flow rates on transfer of titanium dioxide nanoparticles was investigated in the undisturbed soil columns. The flow rate equal to 100, 90, 70 and 50% of the saturated hydraulic conductivity were applied on the soil columns by the peristaltic pump (BT100-1F). By measuring the breakthrough curves for each column, the parameters explaining the transfer of nanoparticles based on a one-site sorption model, one-kinetic site sorption model, and a two-kinetic site sorption model were determined. The results indicate by increasing the flow rate, the reltive concentration of TiO2 nanoparticles (C/Co) in the soil column increases from 3% to 28%. Among the three studied models, the two-kinetic site sorption model which consider the physical straining mechanism based on the particle size and porosity of the porous medium, the function of saturation of the porous media particles with nanoparticles and the physical straining function considering changes of this mechanism with distance, shows the best fit (R2>%90) for estimation of the nanoparticles transfer in the soil column