Abstract

Solid friable residues (i.e. Ash) from combusted oil shale are a major environmental issue because they are highly enriched with toxic elements following combustion. The synchrotron based techniques X-ray Absorption Fine Structure (XAFS) were used for determining the changes in speciation of Chromium (Cr) and Vanadium (V) in the ash and its mixtures with Red soil and Phosphogypsum as additives, through one-year period of hydration process. The X-ray Absorption Near Edge Structure (XANES) qualitative results indicate that all mixtures exhibits similar patterns showing that Vanadium has remain as pentavalent state, on the contrary Chromium has dramatic decreased from hexavalent to trivalent. This change in Cr speciation became clearer with increasing hydration period. Therefore, the results confirmed the advantage of the hydration process in the Cr(VI) reduction which might be due the domination of carbonate phase within all mixtures, thus hydration caused carbonate dissolution that increase the pH toward more alkaline which caused the Cr(IV) reduction into less-harmful and less mobile Cr(III). This increase in pH was not in favor of changing the V(V) into V(IV) due to its large stability field V(V). The Extend X-ray Absorption Fine Structure (EXAFS) analysis showed that Cr exhibiting a coordination shell of C-atoms as first nearest neighbors backscattering atoms around Cr, and at C-atoms backscattering at medium range order. This confirmed the domination of carbonate media through the best fitting of Cr–C. Which might be attributed to the more alkaline conditions developed during saturation of water (hydration), that accelerates of the reduction of Cr(VI) into Cr(III). This means simply that hydration of the ash can reduce the presence of harmful Cr(VI) in these ash tailings.

Highlights

  • IntroductionEl-Lajjoun is the main area containing the Oil Shale, its 110 km to the south of the capital Amman

  • The X-ray Absorption Fine Structure (XAFS) is a powerful element-selective technique that is sensitive to the three-dimensional structure around the photo-absorber, and can effectively probe the defects, vacancies, and distortion in local structure

  • The synchrotron XAFS analytical results confirms the effect of increasing pH (i.e. Alkalinity) as controlling factor in Cr(VI)

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Summary

Introduction

El-Lajjoun is the main area containing the Oil Shale, its 110 km to the south of the capital Amman. Oil shale at Attart Umm Al-Ghudran area Figure 1 Such power plant will provide Jordan with significant electrical power from a domestic source of fuel for the first time. A rough calculation suggests, that a 900 MW thermal power plant would require 6000 tons of oil shale. This would generate 3300 tons of burned oil shale (BOS) ash per day (i.e. 1.2 million tons per year).

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