Evaluating the removal efficiency of potentially toxic elements (PTEs) from a shale deposit by citric acid

Document Type : Original Article

Authors

1 Nuclear Materials Authority

2 Benha University, Faculty of Agriculture, Soils and Water Department

3 Benha University, Faculty of Agriculture, Soils and Water department

Abstract

The majority of arable lands of Egypt are deserts, mainly sandy soils of low fertility, low water retention and high water and wind erodibility. Shale deposits (rich in clay minerals) might be considered suitable conditioners to improve soil physical, chemical and mineralogical properties and hence increase its productivity. However, these additives should not be a source of contaminants such as PTEs. Accordingly, a technical shale deposit sample was collected from Abu Thor (longitudes between 33○ 22″ and 33○ 23ʺ E and latitudes between 29○ 00″ and 29○ 02ʺ N), Southwest Sinai . In this shale deposit sample, silica comprised 37.35% and alumina was about 18.37%. This sample also contained 630 mg Mn, 7704 mg Zn, 19200 mg Fe, 2627 mg Pb, 2763 mg Co and 1310 mg Ni per kg. These levels are not environmentally acceptable in shale deposits when used for soil conditioning. Accordingly, removal or at least reduction in contents of these contaminants in shale deposits should be considered prior to their addition as conditioners to low fertile which exhibit low water holding soils such as the sandy ones. To attain this aim, PVC columns (6.8cm inner diameter× 45cm height) were filled with the shale deposit, washed with citric acid (conc: 10 g L-1) at a flow rate of 1 mL per min. with a total volume of 3200 mL per column and the leachate was collected every 100 min to determine its content of PTEs. Cumulative extracted PTEs were calculated versus time and best fitted to the power function kinetic model. This extraction followed the sequence of Ni>Fe>Co>Pb≈Zn>Mn and, in general, the removal efficiencies were low and did not exceed 12% of Ni, 4% of Co, 2.97% of Mn, 2% of Pb and 1% for each of Fe and Zn. It can; therefore, be deduced that citric acid can only chelate the easily bounded forms of PTEs. More researches are needed to investigate the efficiency of citric acid for in-situ long term facilitated phytoextraction of PTEs from shale deposits to attain more acceptable levels

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History

  • Receive Date: 16 January 2023
  • Revise Date: 11 February 2023
  • Accept Date: 11 February 2023

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