This paper presents the first study on the oil shale (OS) ashing and OS ash leachability of Jordanian OS located further in the south. The studied OS is from Isfir Al-Mahata subsurface OS located 10 km south of Ma’an. Chemical and physical characterization of the OS ash was performed and compared with original OS. Ashing OS was conducted at different temperatures. Important parameters affecting OS ash leachability were also investigated. The leachability of certain heavy metals was investigated based on clear leaching protocol. The Fisher Assay analysis result indicates that this OS type has quite higher moisture content, lower oil content, and higher spent shale compared with other Jordanian oil shales. Ashing of OS at higher temperatures (950°C) resulted in the disappearance of silica, due to its complete reaction with lime and Al, and formation of Anhydrite and cement materials like, Portland cement. The leachability analysis indicates that for most elements the leachability is high at low pH. The released heavy metals concentrations are below EPA limits. Chromium and lead are leached out more than other elements with the exception at low pH. In general, the higher the ashing temperature is, the lower the release of elements is. The chemical composition of the ash and the leachability results suggests that it has high fixing capacity toward the heavy metals present in the ash.
Enormous research work and feasibility studies have been carried out on the Jordanian OS. This indigenous natural fossil fuel remains without utilization. Huge OS reserves are reported to cover large area of the country [
Oil shale development in Jordan requires complex and expensive facilities. Serious economic, environmental, and social implications for Jordan and its people are expected [
Heavy metals found in OS ash could be released to the surrounding environment including surface and groundwater recourses [
Oil shale composite sample was provided from OS core interval of Isfir-1 borehole drilled in Isfir Al-Mahata OS south of Ma’an in the southern region of Jordan (
Oil shale sample was firstly cleaned and then dried. One thin section has been prepared
and studied under the transmitted white light microscope. Part of the sample was crushed then pulverized. The pulverized OS sample was then sieved to several particle size fractions. The bulk density of the sample was determined through the density apparatus. Organic matter ( OM ) content is inferred from the total organic carbon content (TOC) that is measured via carbon determinator. Elements quantitative analysis was obtained by x-ray fluorescence instrument. The X-ray powder diffractometer (XRD) was used for mineral phase identification. The quality of OS is inferred from the Fisher Assay analysis that is obtained via the Fisher Assay apparatus according to ISO 647 by thermal cracking method.
Ashing process was performed according to standard procedure reported by Harahsheh et al. [
The investigated parameters and leaching methodology conditions followed are presented in
The bulk density of OS was found to be 1.4 g/cm3. This is quite lower than that reported for similar material from other OS deposits in Jordan by Alali [
Investigated parameters | Conditions | Other setup conditions |
---|---|---|
1. Mass (g) | Different masses (1, 2, 3, 4) g | Volume (100 ml), time (5 hrs), rpm (700), size (710 - 1400) µm. |
2. Size (µm) | Different sizes (µm) | Volume (100 ml), time (5 hrs), mass (1 g), rpm (700). |
3. Time (hr) | Different time (1, 2, 3, 5, 7, 18, 24) hrs. | Volume (100 ml), mass (1 g), rpm (700), size (710 - 1400 µm) |
4. Speed of mixing (rpm) | Different rpm (300, 500, 900, 1100) | Volume (100 ml), mass (1 g), time (5 hrs), size (710 - 1400 µm) |
5. pH test | pH of the water adjusted by HCl and NaOH solutions | Volume (100 ml), mass (1 g), rpm (700), time (5 hrs), size (710 - 1400 µm) |
6. Effect of temperature on pH value | Temperature and pH | Volume (100 ml), mass (1 g), size (710 - 1400 µm), time (3 hrs), and rpm (700) |
The results of Fisher assay analysis is presented in
The main mineral phases identified Via XRD analysis (
The average content (wt%) of selected metal oxides in the studied OS is presented in
Fe2O3 % | MnO % | TiO2 % | CaO % | K2O % | P2O5 % | SiO2 % | Al2O3 % | MgO % | Na2O % | L.O.I % |
---|---|---|---|---|---|---|---|---|---|---|
1.94 | 0.01 | 0.20 | 28.65 | 0.19 | 1.16 | 5.92 | 0.42 | 0.15 | 49.72 |
OS since this type of OS is rich in terrestrial material indicators [
The XRD results of OS ash resulted from ashing OS samples at different temperatures are shown in
2CaO + SiO2 → Ca2SiO4 (1)
3CaO + SiO2 → Ca3SiO5 (2)
CaO +SO3 → CaSO4 (3)
The chemistry of the ashed samples at different ashing temperatures is presented in
About 1 g of OS ashed at 750˚C was soaked in distilled water and agitated at 700 rpm. The values of pH and conductivity obtained at different conditions are shown in
Type | Fe2O3 % | MnO % | TiO2 % | CaO % | K2O % | P2O5 % | SiO2 % | Al2O3 % | MgO % | Na2O % | L.O.I % |
---|---|---|---|---|---|---|---|---|---|---|---|
Ash 550˚C | 2.584 | 0.012 | 0.265 | 40.484 | 0.280 | 1.697 | 17.06 | 8.702 | 0.631 | 0.278 | 28.00 |
Ash 750˚C | 3.067 | 0.013 | 0.320 | 50.165 | 0.363 | 2.155 | 21.84 | 11.090 | 0.827 | 0.498 | 09.65 |
Ash 950˚C | 3.604 | 0.013 | 0.329 | 51.451 | 0.336 | 2.329 | 24.04 | 12.390 | 0.888 | 0.556 | 04.05 |
Element | Co | Pb | As | Fe | Ba | V | Cr | Cu | Ni | Zn |
---|---|---|---|---|---|---|---|---|---|---|
Concentration, ppm | ||||||||||
Original OS | 20 | 95 | 19 | 13500 | 15 | 75 | 290 | 459 | 204 | 2870 |
Ash at 550˚C | 25 | 112 | 25 | 17070 | 20 | 100 | 385 | 610 | 270 | 3710 |
Ash at 750˚C | 40 | 121 | 28 | 24065 | 50 | 115 | 450 | 1110 | 305 | 4169 |
Ash at 950˚C | 45 | 130 | 30 | 27060 | 50 | 145 | 805 | 1410 | 357 | 4485 |
ture of OS ash. This is also evident from the mineralogy of the ash; CaO in water is converted to calcium hydroxide, which is slightly soluble in water (about 2 g/l at room temperature). From the environmental point of view, high pH when OS ash pH is regarded as advantageous in neutralizing acidic mine drainage (AMD) [
Results show that the pH and conductivity increases as a result of mixing time increase (
Slight increase in pH and conductivity observed due to the increase in mixing rate (
Ashing OS temperature, leaching temperature, and their relation with pH are important factors need to be considered in heavy metal release from OS ash. The effect of ashing temperature on heavy metal release is shown in
The effect of leaching temperature on metal release at wide range of pH for OS ash obtained at different ashing temperatures is shown in Figures 7-10. Generally, metal release is minor. More metal release is obtained at low pH. With increasing leaching temperatures, OS ashes show different patterns of metal release. At low pH, the leachability of the heavy metals analyzed is higher than those at higher pH. Analysis result on the effect of initial pH on final pH of the leachate (see
it is found that all metals higher release. It is also interesting to note that the release of Cr from both original OS and OS ash obtained at 950˚C are lower than that obtained at OS ashes obtained at 550˚C and 750˚C. This could be related to the fact that Cr in the first instance are fixed with the crystalline structure of the mineral phases, whereas, it could available for leaching in a matrix obtained at moderate ashing temperatures where better chances to find easy leachable amorphous phases. Never less, heavy metals
in OS ash are immobile and will not be easily leached to the groundwater by the action of water infiltration. Agitated mixtures resulted in slight leaching of these metals in the present case [
Characterization results of Jordanian Isfir Al-Mahata OS deposit show that the OS has TOC content of 8%. The mineral constituents are calcite, silica as quartz, phosphates as apatite, and minor amounts of clay minerals and pyrite. The average CaO and SiO2 content is 28.65 and 11.64%, respectively. Oil shale ash was also examined and characterized. Ashing OS at 550˚C did not result in any major change in the mineralogical composition. Ashing OS at 750˚C resulted in the appearance of calcium silicate and aluminium silicate and lime, and the disappearance of calcite. Ashing OS at 950˚C resulted in the disappearance of silica, due to its complete reaction with lime and Al, and clear formation of Anhydrite cement materials like, Portland cement Ca3SiO5 + Ca2SiO4. The leachability of heavy metals shows that for most elements the leachability is high at low pH. The leachability of Cr, Cu, Ni, Zn, and Pb is below EPA limits. Chromium and lead are leached out more than other elements with the exception at low pH. In general, the higher the ashing temperature is, the lower the release of elements is.
Alnawafleh, H.M., Al-Harahsheh, M.S. and Al-Harahsheh, A.M. (2016) Leachability of Oil Shale Ash from Isfir Al-Mahata Oil Shale, Southern Jordan. Journal of Minerals and Materials Characterization and Engineering, 4, 292-303. http://dx.doi.org/10.4236/jmmce.2016.45026