Effects of Moisture Content and Voltage Gradient on the Removal of Cd, Pb and Zn From a Calcareous Contaminated Soil

Document Type : Research Paper

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Abstract

Electrokinetic removal of heavy metals from the contaminated soils seems an innovative approach for their remediation. This technique may require much less time for the removal particularly in the soil with lower permeability comparing to the conventional leaching methods. In the current study electrokinetic remediation of a calcareous soil contaminated by three heavy metals (Zn=1400 mg kg-1, Cd=15 mg kg-1 and Pb=250 mg kg-1) due to the release of sludge's from mining industry around Zanjan city north west of Iran, was investigated in disturbed soil columns. Treatments imposed during the experiment were three moisture contents (saturated, FC and 0.7 FC), and two voltage gradients (1.3 and 2.66 volts per cm of the column length). Effects of three electrolytes (distilled water, Acetic acid, EDTA), electrolyte circulation and anodes displacement on the removal efficiency were also studied. Experimental data showed that raising voltage gradient and water content both enhanced ion migration through the column and thus led to considerably grater removal. After 10 days imposing the above voltage gradient under saturation condition, the removal of Cd, Zn and Pb achieved to 32.6%, 31.3% and 18.9%, respectively. Reducing water content to 0.7 FC reduced the removal percents to 21%, 18.4% and 12.3%, respectively. The largest removal belonged to Cd; with Zn and Pb being the second and third in this respect.

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1-   کارایی حذف فلزات سنگین در رطوبت اشباع نسبت به رطوبتهای دیگر بالاتر بوده و با کاهش رطوبت، درصد حذف فلزات سنگین کاهش می­یابد.
2-   تأثیر افزایش شیب ولتاژ در تیمارهای مختلف بر کارایی حذف فلزات سنگین نتایج متفاوتی دارد و در تیمار آندهای نزدیک شونده  و تیمار EDTA افزایش شیب ولتاژ بالاترین افزایش در کارایی حذف فلزات سنگین را دارد.
3-   موادی مانند EDTA به علت قدرت کمپلکس کنندگی بالا کارایی حذف فلزات سنگین توسط روش الکتروسینتیکی را تا حد قابل توجهی افزایش می­دهند.
4-     استفاده از مواد اسیدی در خاکهای آهکی در افزایش کارایی حذف فلزات سنگین چندان مؤثر نمی­باشد.
5-   استفاده از سیستم جریان گردشی به عنوان تعدیل کننده pH در خاک­هایی که ضریب آبگذری پایینی دارند در شیبهای ولتاژ بالا در افزایش کارایی حذف فلزات سنگین چندان موفقیت آمیز نمی­باشد.
 
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Water and Soil Science
Volume 19, Issue 1
May 2009
Pages 177-199

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