Characterization and utilization of solid residues

ORIGINAL ARTICLE

Characterization and utilization of solid residues generatedupon oil and heat production from carbonate-rich oil shale

B. S. Al-Saqarat1 • K. M. Ibrahim2• F. M. Musleh2 • Y. S. Al-Degs3

Received: 24 December 2016 / Accepted: 20 March 2017

� Springer-Verlag Berlin Heidelberg 2017

Abstract The utilization of a newly discovered Jordan-

origin oil shale was outlined in this work. Both industrial

and environmental issues were discussed for better han-

dling the wastes that often generated upon processing of oil

shale. Two by-products of oil shale were studied, retorted,

and combusted oil shale. The wastes were produced under

different conditions. Different analytical techniques (XRF,

XRD, proximate analysis, infrared spectroscopy, particle

size distribution, TGA/DSC, and ultimate analysis) were

used to follow up the physicochemical changes in gener-

ated solid residues. Oil shale was rich in carbonate with

spent content of 73.2%. Upon processing oil shale, many

heavy metals were concentrated in the final residue. The

most concentrated metals were Cr, Cu, Co, and V with

enrichment factor more than 2.0 in both residues. Com-

pared with raw oil shale, leaching of toxic heavy metals

was increased many folds and percentage of extraction was

higher than 60% of all metals using HNO3. Total charac-

teristic leaching tests TCLT, a standard test to stimulate

metals elution in the environment, confirmed that retorted

oil shale was more toxic when contacted with aquatic

environment. TCLT indicated that the released amount of

Cr was 4.4 higher than the safe limit set by international

agencies. Elemental analysis indicated that H/C ratio of oil

shale was 0.11 and hence would be used as low-grade fuel.

The maximum content of kerogen was 19%, which is

estimated by Soxhlet extraction with methanol. The best

utilization of retorted and combusted solid residues was as

solid medium for Pb ions and phenol removal from solu-

tion. Retorted oil shale has better efficiency toward phenol,

while combusted oil shale exhibited better removal for Pb

ions. Gross heating value, textural parameters, density, and

Si/Al ratio were found useful indicators to assess the best

utilization of solid wastes generated upon oil shale

processing.

Keywords Oil shale � Retorted oil shale � Combusted oil

shale � Waste handling � Adsorption � Metals leachability

Introduction

Geologically, oil shale (OS) is composed of a fine-grained

sedimentary rock having organic matter (5–22%) that gives

large amounts of oil and combustible gases upon retorting

(Patterson et al. 1986). Compared with gulf countries and

Egypt, Jordan has limited sources of crude oil and natural

gas. However, there are large deposits of oil shale in the

country. Jordan is listed among the top five countries rich

in oil shale (Al-Harahsheh et al. 2012). Up to now, the

practical utilization of OS for oil production at national

level is under investigation. The high fluctuation in the

prices of crude oil is the main reason behind the urgent

need for utilization of OS on a global scale (Al-Harahsheh

et al. 2012). The most investigated OS was originated from

El-Lajjun as indicated in the scientific literature (Alali

2006; Ibrahim and Jaber 2007; Al-Harahsheh et al. 2012).

The estimated volume of shale oil (i.e., the oil extracted

from OS) that would be produced from the global OS is 30

times higher than the available crude oil (Russell 1990; Al-

& Y. S. Al-Degs

[email protected]

1 Department of Geology, The University of Jordan,

P.O. Box 11942, Amman, Jordan

2 Department of Earth and Environmental Sciences, The

Hashemite University, P.O. Box 150459, Zarqa, Jordan

3 Department of Chemistry, The Hashemite University,

P.O. Box 150459, Zarqa, Jordan

123

Environ Earth Sci (2017) 76:264

DOI 10.1007/s12665-017-6578-9

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Harahsheh et al. 2009). Increasing local demand for pro-

ducing energy has initiated many national projects for OS

utilization (Al-Harahsheh et al. 2012). As already known,

oil shale has been explored in Jordan since 1960 (Alali

2006). Governmental reports indicated that 65 billion tons

of OS is available in Jordan and 85% of this solid material

is located in the central part of the country (Alali 2006).

Extraction of shale oil (also known as kerogen) and

using as low-grade fuel were the main utilization practices

of OS. In general, extraction of kerogen represents 90% of

overall oil shale usage (Speight 2012). Extraction of oil

needs conversion the solid hydrocarbons in OS to kerogen

which pumped and processed in another stage (Speight

2012). Basically, extraction of kerogen is accomplished by

direct heating of the rock to a high temperature and low

oxygen content and then separating the resulting oil

(Speight 2012). This process is known as retorting (Hutton

1987; Speight 2012). Extraction of kerogen from OS would

be accomplished by two procedures, surface retorting and

in situ retorting (Russell 1990; Speight 2012). In situ

retorting is more applicable as surface retorting required

large land and high water consumption (Speight 2012).

In situ retorting, oil is directly extracted and recovering of

deeply located OS is easily accomplished (Speight 2012).

In this advanced procedure, OS is gradually heated

underground and the collected oil and gas are directly

extracted from the site just like pumping crude oil (Speight

2012). Currently, the Jordan Oil Shale Company (JOSCO)

has been demonstrated the efficiency of extracting kerogen

in many locations over Al-Azraq area using in situ retort-

ing. Beside in situ retorting, extraction of kerogen from

powdered OS by organic solvents seems to be achievable

on commercial scale with high percentage yield (Al-Alla

and Nassef 2015; Nassef et al. 2015). Using kerogen as a

potential substituent for crude oil was an essential research

area and received important attention in the last few

years (Kumar et al. 2013).

The main disadvantage that associated with surface

retorting, in situ retorting, and combustion of OS was the

large amount of residues (Speight 2012). Recently, there

were growing concerns on the environmental impact of spent

oil shale. In natural form, oil shale is harmless and has no risk

when it remains in situ and even after long exposure to rain or

ground waters (Speight 2012; Snape 2012; Naseef et al.

2015). All types of spent oil shale have, in fact, serious

environmental consequences if utilized in the wrong place or

wrong time (Speight 2012; Snape 2012; Naseef et al. 2015).

The reported studies clearly indicated that retorted oil

shale and combusted oil shale contain much more metals

than the original material (Alali 2006; Ibrahim and Jaber

2007; Al-Harahsheh et al. 2012). Accordingly, concerns

about the impacts of spent oil shale on the environment and

human health should be carefully considered. Depending

on utilization practices, oil shale often generates three

types of pollutants (Speight 2012): (1) S and N gases, (2)

liquid residues including water saturated with unwanted

chemicals, and (3) solid residues or spent oil shale. Indeed,

emission of N and S gases and leaching of toxic heavy

metals from spent oil shale were listed as the top envi-

ronmental issues related to full utilization of OS (Alali

2006; Ibrahim and Jaber 2007; Al-Harahsheh et al. 2012).

The previous studies confirmed that leaching of heavy

metals was higher in retorted OS compared to natural OS.

Accordingly, detailed chemical tests on metals leaching

from spent or combusted oil shale are essential prior to

final discharging of the wastes of OS. A detailed literature

survey was carried out to evaluate the possible utilization

of retorted or combusted oil shale. Most studies investi-

gated the leaching of heavy metals including Cr, Mn, Co,

V, Zn, and Cu from spent oil shale (Michael and Surendra

1991; Al-Asheh et al. 2003; Ibrahim and Jaber 2007; Bai

et al. 2008; Al-Harahsheh et al. 2012; Goren 2015). Bai and

co-workers have systematically investigated the migration

behavior of toxic heavy metals from OS and other forms

subjected to high temperatures 360–560 �C (Bai et al.

2008). The reported results indicated that leaching of

metals was higher for retorted OS at 560 �C (Bai et al.

2008). The authors outlined that leaching tests by different

solvents were essential before the final discharge of spent

OS (Bai et al. 2008). Ibrahim and Jaber have studied the

physical and chemical properties of El-Lajjun retorted OS

and outlined that the residue was rich in Ca and Si along

with many heavy metals (Cr, Ni, Zn, and Cu) (Ibrahim and

Jaber 2007). The authors do not test the leachability of the

metals from the waste; however, they outlined that the best

utilization of spent OS was for Pb ions removal from water

(Ibrahim and Jaber 2007). In an interesting study, Fu et al.

(2013) investigated the migration behavior of many metals

including Se, Cd, Mo, As, Cs, Pb, Sr, and U while com-

bustion of marine oil shale for sake of heat production. Al-

Harahsheh et al. (2012) investigated the leachability and

environmental impact of combusted El-Lajjun OS. The

reported results proved that combusted OS combusted at

650 �C can leach heavy metals like Cd, Pb, Zn, Cu, and Cr

but in amounts below the safe levels set by the Environ-

mental Protection Authority (Al-Harahsheh et al. 2012).

Moreover, the level of leached heavy metals increases with

ashing temperature as a weaker matrix would generate at

higher temperatures (Al-Harahsheh et al. 2012). Upon

extraction of heavy metals from spent residues, the other

useful applications including solid adsorbents (Shawabkeh

et al. 2004), carbon-based adsorbents (Mohan and Pittman

2006), geopolymers (Zarina et al. 2013), and ingredients

in construction materials (Paiste et al. 2016) would be

judged but after detailed physical and chemical

examinations.

264 Page 2 of 17 Environ Earth Sci (2017) 76:264

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In this work, the following aims are intended to be

achieved to find the best utilization of two possible waste

forms of oil shale including retorted and combusted OS.

Initially, surface characterization of a newly explored oil

shale in Al-Azraq area (70 km east Amman) was carried

out including XRD (for mineral identification), XRF (for

chemical identity), TGA/DSC (for pyrolysis temperature,

phase transformation and stability to heat), particle size

distribution, oil/spent shale assay, gross heating value,

textural properties (surface area and pore volume), and

leachability of toxic heavy metals by different solvents.

Based on the characterization outputs, the best utilization

of retorted and combusted oil shale as potential wastes is

discussed. The possible utilization practices of wastes are:

precursor for geopolymer, ingredient with construction

materials, filling materials, fertilizers, soil stabilizers, pre-

cursor for zeolites, adsorbents for heavy metals and

harmful organic pollutants, and as low-grade fuel for power

generation or domestic heating.

Experimental

Materials: oil shale, retorted and combusted forms

About 5.0 kg of natural oil shale, provided as a hard rock,

was donated by Jordan Oil Shale Company JOSCO (Am-

man, Jordan). The sample was obtained from a deep

borehole drilled in Al-Zraq area, 70 km east Amman.

JOSCO is a leading company and has excellent experience

in shale oil retorting and purification (JOSCO 2016). The

sample was crushed by a hammer and then sieved into

different particle sizes, and sample size less than 100 lmwas used in leaching and adsorption tests. The powder was

stored in a plastic bottle and tightly closed to prevent

moisture uptake. The sample was used in all tests without

further purification. About 3.0 kg sample of retorted oil

shale was kindly donated from JOSCO. The sample was

procured from the field where shale oil was extracted using

in situ technology from a newly discovered location in Al-

Azraq area. Initial sieving tests indicate that 75% of the

sample was fine powder with particle diameter less than

100 lm. The fine portion (\100 lm) was stored in a tightly

closed plastic bottle to minimize moisture uptake. The

retorted oil shale was used as received in adsorption and

leaching tests. Combustion of oil shale was carried out in

our laboratory as follows. Before combustion, 25.0 g of oil

shale was crushed and sieved to homogenous particle

diameter less than 1.0 mm. The powder was placed in a

quartz dish and heated in a muffle furnace at 750 �C under

atmospheric conditions. Heating rate was 10 �C/min, and

the samples were heated for 40 min to ensure full com-

bustion of the oil within the internal pores of the sample.

Reagents and solutions

HNO3, NaCl, NaOH, CH3COOH, Pb(NO3)2, and C6H5OH

were purchased as analytical-grade chemicals from BDH

(UK). For metals leaching test, 1.0 M solution of HNO3,

NaCl, and NaOH was prepared by dissolving or diluting

the appropriate amounts in a 1.0-L volumetric flask and

diluting by distilled water. For toxicity characteristic

leaching test TCLT, 0.1 M solution of acetic acid was

prepared by diluting appropriate amount of acetic acid to

final volume of 1.0 L using distilled water. For Pb

adsorption from solution, 1000 mg/L Pb stock solution was

prepared by dissolving 1.60 g of Pb(NO3)2 in 10 ml dis-

tilled water and the final solution was toped up to 1.0 L

using distilled water. From Pb stock solution, diluted

solutions were prepared for adsorption tests using distilled

water as diluent. For phenol test, 1000 mg/L stock solution

was prepared by dissolving 1.00 g in a small amount of

water, stirring for 10 min, and diluting to a 1.0 L by dis-

tilled water. From the stock solution, diluted solutions were

prepared for adsorption tests using distilled water as

diluent.

Instruments and measurements

XRD patterns were recorded using Shimadzu X-Ray

diffractometer (Shimadzu X-Ray Diffractometer XRD-

6000). The scans were recorded over 2h 4–80 with a step of0.02 using X-ray operated at 40 kv. Scanning electron

micrograph–energy-dispersive X-ray spectrometry SEM/

EDX (FEIINSPECT-F50-SEM/EDX) was used for viewing

the surfaces at high magnification powers (950,000) and

for metals detection on the surface. The contents of heavy

metals in the solid materials were measured by X-ray flu-

oresce spectroscopy (Shimadzu XRF-1800 Sequential

X-Ray Fluorescence Spectrometer). Textural characteris-

tics including specific surface area and total pore volume

were measured by surface area and pore size analyzer

which is based on N2 adsorption at 77 K (Nova 4200e,

Surface Area and Pore Size Analyzer). Gas chromatogra-

phy was applied for C, H, N, and S quantification (ELTRA

CW multiphase determinator). For alkali metals (Ca, K,

and Na) quantification, Jenway flame photometer was

applied (Jenway). For monitoring thermal stability and

phase changes in solid materials, thermal and differential

scanning calorimeter was used (PerkinElmer, USA). Par-

ticle size distribution of powders was measured using laser

technology (Microtrac Zetatrac, Microtrac, Particle Size

Analyzer). PerkinElmer Dynascan Interferometer AVI

(USA) was used to measure IR spectra of samples over the

range 400–4000 cm-1. Samples were placed in a small

crystal cup (50 mm diameter and 10 mm depth) before

scanning. The temperature of sample holder was controlled

Environ Earth Sci (2017) 76:264 Page 3 of 17 264

123

at 25 �C. The spectra were subtracted against background

air spectrum. The content of phenol in solution was mea-

sured using simple spectrometry (UV/Vis spectropho-

tometer, PerkinElmer). Ultimate analysis of solid residues

was carried out according to standard procedures (ASTM

D3172 2013). Oil content was quantified by methanol

extraction as outlined in the literature (Al-Alla and Nassef

2015). A 100-g powdered oil shale was placed in a metal

dish and heated in the furnace at 200 �C for 10 min under

flow of N2 gas. After this step, the dish was closed and re-

heated at 300 �C for 1.5 h under flow of N2 gas. The heated

OS was placed in the thimble to start Soxhlet extraction

with 200 ml of an organic solvent. Many organic solvents

were tested in this regard including methanol, ethanol,

acetone and tetrahydrofuran. The mixture was extracted for

6.0 h to ensure oil recovery. Finally, the mixture was fil-

tered, and the dark-brown organic layer was distilled to

remove the solvent. The collected oil was dried under

vacuum and weighted. The solid residue was removed from

thimble, dried, and weighted to estimate the amount of

spent oil shale.

Metals leaching from solid materials by different

solvents

In fact, the tested reagents are known of their high extraction

efficiency of metal from solid residues (Kosson et al. 2002).

All extraction tests were carried out using 1.0 M solution,

and the ‘‘liquid to solid’’ ‘‘L/S’’ ratiowas fixed at 50.0 cm3/g.

Typicality, 200 ml solvent was contacted with 4.0 g sample.

The mixture was mechanically agitated for 4.0 h at 25 �C(±2 �C). The particles of solid materials were removed by

centrifugation (5000 rpm), and the clean supernatant was

analyzed for metals using flame photometer for Ca, Na, and

K ions and atomic absorption spectrometer for Cr, Ni, V, Co,

and Cu ions. Due to the hydrophobic nature of oil shale

particles, methanol (1.0 ml) was added as a wetting agent,

and this helped for soaking the floated fine particles (Pakalns

1983). There was no need to add methanol in the case of

retorted and combusted wastes. For total characteristic

leaching test TCLT, the same experimental procedure was

repeated using 0.1 M acetic acid solution (Pandey et al.

2012).

Removal of Pb ions and phenol as model pollutants

from solution

As will be discussed later, the best utilization of retorted

and combusted OS was as solid adsorbent. Accordingly, all

solid residues were tested to remove Pb ions and phenol

from model solutions. Concentration–variation adsorption

isotherms were conducted for Pb ions and phenol adsorp-

tion from solution by ROS and COS. Adsorption of Pb ions

was carried out over the concentration range 2.0, 4.0, 6.0,

8.0, 10.0, 12.0, 16.0, 18.0, and 20.0 mg/L, while adsorption

of phenol was investigated over the concentration range

3.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0, and

50.0 mg/L. For both systems, pH was adjusted to pH 5.0 to

prevent the hydrolysis of Pb ions and keeps phenol in its

H-form (pKa of phenol 10.0). Typically, 0.5 g of dried

solid material (diameter less than 100 lm) was added to a

100 ml of adsorption solution. The flasks were closed and

agitated in a thermostated shaker (GEL, Germany) for 5 h

(for Pb) and 20 h (for phenol). The equilibrium times (5

and 20 h) were determined in separate kinetic runs. In all

cases, 1.0 ml methanol was added as a wetting agent to

help fine oily particles to soak in the solution (this was

necessary for oil shale adsorption test). Solid particles were

removed from solution by centrifugation at 2000 rpm for

5 min. For Pb adsorption test, the solutions were directly

measured by atomic spectrometry at 405.8 nm and phenol

was directly measured by double-beam spectrophotometer

at 270 nm.

Adsorption isotherm

Before modeling adsorption data, it was necessary to

estimate surface concentration qe (mg/g) and equilibrium

concentration Caq (mg/L) for the pollutant after attainment

of adsorption process. qe is estimated according to Issa

et al. (2016):

qe ¼ðCo � CeÞ � V

mð1Þ

where Co, Ce, qe, V and m are the initial solute concen-

tration (mg/l), the equilibrium concentration (mg/l), surface

concentration (mg/g), volume of solution (L), and mass of

adsorbent (g), respectively.

Langmuir isotherm

Langmuir’s isotherm is based on the assumption that

adsorption energy is constant and uptake occurs on

homogeneous surface by monolayer adsorption (Allen

et al. 2004). When the surface is covered by a monolayer of

adsorbate, the adsorption goes on localized sites with no

interaction between adsorbate molecules. Assuming equal-

energy active sites and no reaction between adsorbed

molecules, then Langmuir equation is presented as (Issa

et al. 2016):

qe ¼KLQmax

ð1þ KLCeÞð2Þ

where qe (mg/g), Ce (mg/L), KL (L/mg) and Qmax (mg/g)

are surface concentration of adsorbate at equilibrium,

concentration of adsorbate remaining in solution at


123

equilibrium, a constant that relates to the adsorption

intensity, and the maximum adsorbed quantity of adsor-

bate, respectively.

Freundlich isotherm

Freundlich model has empirical nature and based on

adsorption by heterogeneous surface and has the general

expression (Issa et al. 2016):

qe ¼ KFCne ð3Þ

whereKF (mg/L) and n are equilibrium constant indicative of

relative adsorption capacity and model exponent which

characterize quasi-Gaussian energetic heterogeneity of the

surface (Ho 2004). A favorable uptake of adsorbate is indi-

cated by higher n value 1–10 (Allen et al. 2004; Ho 2004).

Assessment of models and errors estimation

The parameters of both models were estimated following a

nonlinear fitting procedure. Data solver (Excel�) was

adopted to run all necessary calculations. The degree of fit

of the models to the experimental data was evaluated by

estimating Chi-square value X2, which is estimated as

follows (Ho 2004):

X2 ¼XN

i¼1

ðqe;exp � qe;predÞ2

qe;predð4Þ

where qe,pred. and qe,exp are the predicted and experimental

adsorption values, respectively. In Eq. 4, N is the number

of experimental points. Higher X2 value reflects the poor

fitness of the model.

Results and discussion

Surface characterization of solid materials

for environmental assessment

Different physicochemical tests were adopted to evaluate

the environmental impact of processed oil shale samples

that investigated in the current work.

XRF and XRD: elemental and mineralogical

measurements

Solid materials were analyzed by XRF to measure the

contents of metals. Table 1 summarizes the final results.

Enrichment factors (EFs) were estimated for metals in ROS

and COS against natural OS to assess the effect of treat-

ment conditions of OS on metals distribution in the wastes.

As indicated in Table 1, natural OS has high inorganic

nature where Ca and Si were making more than 40% of the

material, and this was also observed in El-Lajjun OS (Al-

Harahsheh et al. 2009). As Ca is making about 28%, then

the current OS was categorized as carbonate oil shale

(Kumar et al. 2013). From Table 1, Si/Al was 12.5 indi-

cating the modest content of aluminosilicate as the typical

ratio should be within 1.85–3.0 (Panda et al. 2010; Al-

Bakain et al. 2014). Si content in OS also reflected the

existence of quartz mineral in substantial level, and this

reported in other local OS like Sultani and El-Lajjun (Al-

Harahsheh et al. 2009). As reported in local (Al-Harahsheh

et al. 2009, 2012), regional (Goren 2015), and international

oil shale (Kumar et al. 2013), toxic heavy metals including

V, Cr, Ni, Cu and Zn were available in large amounts

(160–648 ppm). Compared with other regional and inter-

national OS, the levels of Zn and V were high and

reflecting the industrial importance of the newly discovered

OS. The interesting point in Table 1 is the large variation

in EF of major and minor metals. After kerogen extraction,

EF values were ranged from 0.5 (for Fe) to 3.7 (for V).

However, for COS EFs were ranged from 0.1 (for V) to 3.3

(for Cu). In fact, the stable EFs (0.9) of Ca in both residues

were attributed to its large fraction in the materials. It

seems that both Si and Al did not leave the matrix upon

retorting and combustion as their EFs were higher than 1.0.

Both metals would involve in other phase changes rather

leaving with other combustible materials. The migration of

Fe and Ni with kerogen is possible as inferred from their

low EF. The low EF of S atom (0.9) in combusted OS has

indicated S removal from the matrix as SO2 gas. After

retorting, the interaction of S with other elements is

Table 1 XRF outputs along with enrichment factors for the metals

Metal OS ROSa COSb Enrichment factor EF

ROS/OS COS/OS

Na% 0.20 0.24 0.21 1.2 1.0

Mg% 0.19 0.30 0.38 1.6 2.0

Al% 1.25 2.10 2.40 1.7 1.9

Si% 15.20 21.25 21.40 1.4 1.4

P% 0.85 1.40 1.52 1.6 1.8

S% 3.28 3.48 2.88 1.1 0.9

K% 0.35 0.66 0.63 1.9 1.8

Ca% 28.32 25.55 26.88 0.9 0.9

Fe% 0.95 0.45 1.76 0.5 1.9

V ppm 204 748 13.6 3.7 0.1

Cr ppm 277 455 816 1.6 2.9

Ni ppm 237 210 395 0.9 1.7

Cu ppm 160 255 522 1.6 3.3

Zn ppm 648 895 1134 1.4 1.8

Co ppm 160 262 325 1.6 2.0

a Heating temperature is 520 �C (in situ retorting)b Direct combustion at 750 �C in atmosphere


123

possible as EF of S was higher than 1.0. The extremely

high EF of V in ROS would indicate the accumulation of

this metal in the solid residue rather leaving with kerogen.

However, the same metal (V) seems to leave the matrix

upon composition with O2 as inferred from the low EF

(0.1). The best source of V, of course, is ROS not COS.

The metals (Cr, Cu, and Co) have high EF in COS indi-

cating the formation of stable oxides upon heating at

750 �C in the presence of O2. Accordingly, the best source

of (Cr, Cu, and Co) is COS. Following the above conver-

sation, XRF analysis was significant for selection of the

proper residue for metals recovery.

Although ROS and COS were enriched with Ca, K, Mg

and Na, the direct application as fertilizer is not possible

unless toxic metals were removed in a separate step.

Accordingly, direct application of COS and ROS as

potential fertilizers would be ecumenically not feasible.

The mineralogical constitutions and possible phase

changes in oil shale and other residues were monitored by

recoding XRD scans. Labeled XRD scans of the samples

are depicted together in Fig. 1.

In fact, XRD is the most adopted technique for surface

characterization of oil shale (Kumar et al. 2013). For better

detection of crystalline phases, the scanningwas carried out at

highpower (40 kV).At high scanningpowers, the detectionof

low-level crystalline phases is possible and can give

detectable diffraction peaks in XRD pattern (Muhammad

et al. 2011). Stable and noise-free scans with sharp peakswere

obtained as indicated in Fig. 1. From the XRD scans, the

crystalline phases in the sampleswere identifiedby the search-

match-program available with the instrument. Identification

of phases is based on inter-planner distances and intensity of

the peak value. Moreover, identification of phases was also

made by comparing XRD pattern of pure phases with those

shown in Fig. 1. XRD analysis indicated the domination of

crystalline phases compared to amorphous phases as

confirmed from the sharp XRD lines over the entire range

4–80. For the three samples, almost identicalXRDpatternwas

observed and the main difference was the new peak of high

intensity that observed in the pattern ofCOS (diffraction angleFig. 1 XRD scans of OS and other solid wastes

ROS (magnification×4000)

COS (magnification×16000)

OS (magnification×917)

Fig. 2 SEM of OS and related solid residues recorded at different

magnification powers


123

25.6). Fourteen XRD peaks were positioned at 21.0, 23.8,

26.9, 29.7, 32.4, 36.2, 39.7, 43.4, 47.7, 48.8, 57.6, 60.9, 64.9,

and 65.8 and observed in the three scans. Among the detected

peaks, the highest intensitieswereobserved at 26.9, 29.7, 39.7,

47.7, and 48.8. In fact, phase identification in real soils would

be a hard geological job due to the lower content of some

phases and the possible overlapping between the patterns.

Basedon library searchprovidedwith the instrument, the clear

peaks at (2h) degree 23.8, 29.7, 36.2, 39.7, 43.4, 47.7, 48.8 and57.6 represented calcite (CaCO3) mineral. Besides calcite,

other major minerals that detected in the sample were

kaolinite and quartz. The high intensity of CaCO3 peaks

revealed the high content of this mineral, and this result is in

agreement with XRD analysis as all samples were rich in Ca

(Table 1). The significant reduction in the intensities of peaks

in the range 2h 30–50 observed in COS was an indication of

partial damageof calcite under high temperature.BothOS and

ROS showed comparable patterns, which reflected that

CaCO3 did not highly affectedunder retorting conditions.The

other detected crystalline phase was quartz, which is evi-

denced from the clear peaks at (2h) degree 26.7, 50.3 and 60.0.In fact, 26.7 is a characteristic ofXRDpeak for quartz, and the

existence of Si was also confirmed by XRF. XRD evidenced

the presence of clay minerals (smectites) (in small level) in

COS.Theonly identifiedpeakwas positioned at 2h25.5with agood intensity as indicated in Fig. 1. The characteristics of

XRDpeaks of kaolinitewere appeared at 12.0 and 25.5 (Panda

et al. 2010; Al-Bakain et al. 2014). The absence of other

smectite peaks was attributed to low level of the minerals or

overlapping with the peaks of calcite. The samples have high

crystalline nature as noweak humpwas observed in 2h 20–30,which is common for amorphous materials.

Morphological features and detection of metals

on the surface: SEM/EDX

Monitoring of morphological features upon OS retorting

and combustion is necessary at this stage. Moreover, SEM

would reveal the development of porosity and changes in

crystallinity or amorphous nature in the material at high

temperatures. Accordingly, the morphological features of

the solid surfaces along with detected metals were inves-

tigated by running SEM/EDX tests, and the results are

presented in Figs. 2 and 3.

SEM pictures of the samples were taken at different

magnification powers (9900–16,000) as shown in Fig. 2.

SEM is often combined with EDX (Fig. 3) for scanning

solid surfaces and viewing the pores and to detect the

elements making up the surface. Based on SEM, the

distribution of minerals in OS and homogeneity of the

surface and phase distribution with temperature could be

assessed. The carbonaceous nature of OS and the presence

of plant or animal residues were deduced from the

pictures taken at 9917. The flakes and the pores indicated

organic nature and the presence of kerogen in the sample.

Identical SEM pictures were reported for local oil shale

samples (Al-Harahsheh et al. 2009). For retorted oil shale,

SEM indicated the incomplete removal of kerogen as

confirmed by detected shale or flakes in the sample which

pictured at 94000 magnification power. Moreover, the

formation of small crystals mainly for calcite was an

indication of effect of temperature (520 �C) on OS matrix.

The significant removal of organic matter from oil shale

and development of higher crystalline phases was clearly

depicted in plate 3, which was taken at very high mag-

nification power (916,000). As will be outlined in the

following section and in agreement with SEM, the carbon

content for the three residues was increasing in the fol-

lowing order: combusted oil shale\retorted oil shale\oil

shale. Also, analysis revealed that ash contents in the

samples decrease in the following trend: combusted oil

shale[ retorted oil shale[ oil shale. The identification of

calcite and quartz minerals in ROS and COS through

SEM was carried out by comparing their morphological

features with those provided in petrology Atlas of Welton

(Welton 1984). Based on that, the spherical white crystals

were represented both calcite and quartz phases. Other

textural parameters including surface area and pore vol-

ume were measured to give better judgment on the

environmental applications of the solid residues as will be

outlined soon. EDX spectra of the samples indicated the

elements on their surfaces. The detection of Ca in all

surfaces was observed in the samples with high concen-

tration and this was expected due to the high level of Ca

in the matrices. The detection of P in the sample along

with Ca indicated the presence of apatite. The detection of

Zn on the surface of ROS was evidenced in the ROS

spectra (appeared at 8.5 keV in the spectra), and this was

in agreement with XRF data where Zn had a high

enrichment factor (1.4) and may be concentrated on the

surface under the high temperature of retorting process.

The detection of Fe (appeared at 6.5 keV in the spectra)

on the surface of COS was evidenced in EDX spectra, and

this was in agreement with XRF data where Fe had a high

enrichment factor (1.9) and concentrated on the surface.

The absence of Si peak in the spectra would be attributed

to the overlapping with other peaks (Fig. 3). Presence of

considerable amounts of both Zn and Fe along with S in

ROS and COS samples may reflect the occurrence of

sphalerite (ZnS) and pyrite (FeS2) minerals.

Ultimate, proximate, and oil analyses

Chemical nature of OS and other residues was also

investigated by running standard chemical tests, and the

final results are compiled in Table 2.


123

Oil shale

Retorted oil shale

Combusted oil shale

Fig. 3 Energy-dispersive X-ray

spectrometry of oil shale and

other related residues


123

As indicated in Table 2, proximate analysis revealed that

ash content of solid materials was decreasing in the follow-

ing order COS[ROS�OS, and this reflected the stripping of

oil in the retorting and combustion processes. On the other

hand, percentage of volatile matter (measured at 525 �C)was notably reduced in the reverse order to the one observed

for ash content (see Table 2). Fixed carbon that measured

after combustion at high temperature showed similar trend to

the one observed for volatile matter. Fixed carbon was rel-

atively high comparedwith other Jordan-origin oil shale (Al-

Otoom et al. 2014), and this would be attributed to the

presence of inorganic C in calcite mineral. The interesting

point in approximate analysis was the inefficient removal of

volatile matter in COS (which previously heated to 750 �C),and this was attributed to the encapsulation of organic matter

within the inner matrix. In fact, comparable ash and volatile

matter contents were reported in the popular Jordanian El-

Lajjun OS (Al-Harahsheh et al. 2009, 2012). As already

known, Fisher test is the common procedure that often used

to measure the level of oil, emitted gasses, water and spent

material in oil shale (Speight 2012). In this work, a simple

analytical protocol was followed to measure the level of oil

and spent shale (Al-Alla andNassef 2015). In this procedure,

OS was initially heated at 250–300 �C for 2 h and then

extracted by different organic solvents. Among the tested

organic solvents, methanol was achieved the maximum

recovery of oil fromOS. In fact, the proposed procedurewas

reliable as it gives reasonable oil level in OS (19.82%;

Table 2). Oil content in the current OS was relatively high

when compared with other local OS (Ibrahim and Jaber

2007). In a similar study, the level of oil was 14.5% in El-

Lajjun OS (Ibrahim and Jaber 2007; Al-Harahsheh et al.

2009). In fact, retorting process was carried out underground

in O2-poor environment, and the complete recovery of

kerogen was not achieved as deduced from the good level of

oil detected in ROS (4.7%). The final level of oil was very

modest in COH, which go down to 0.4% indicating the

intensive combustion of the material at 750 �C (Table 2).

Ultimate analysis of initial OS indicated the high levels

of C (23.1%) and H (2.61%), consistent with the presence

of kerogen. The high content of S (Table 2) is unfavorable

due to possible emission of SOx when using OS as fuel for

heat generation. Level of S in OS was significantly lower

than those detected in Jurfed Darawish and El-Sultani

deposits (Al-Alla and Nassef 2015). H/C ratio would

indicate the combustion quality of a fossil fuel; the lower

ratio implies better combustion quality (Kumar et al. 2103).

The H/C ratios were 0.11, 0.06, and 0.16 for OS, ROS, and

COS, respectively. This result implies the possible appli-

cation of OS and ROS as low-grade fuel in power stations.

Ash and spent oil contents (Table 2) indicated the

presence of high level of inorganic matter rich in Ca and Si,

consistent with XRF data.

Monitoring of structural changes by thermal

stability and infrared spectral analysis

Thermal behavior of solid residues was measured. Both

TGA and DSC are depicted in Fig. 4.

It is important to mention that measuring TG and DSC

of OS should not carried out at heating rates higher than

5 �C (Wang et al. 2016). TG curves measured at heating

rates of 10 and 30 �C were unstable and did not give any

informative information on thermal stability (Wang et al.

2016). As shown in Fig. 4a, thermal behavior of OS indi-

cated two thermal decomposition stages, around 150 and

350–400 �C. The first stage corresponds to moisture

vaporization, while the second stage that contributed to a

high mass loss (20%) resulted from the decomposition of

kerogen and other heavier organic matter in the sample

(Wang et al. 2016). DSC indicated the presence of two

small endothermic peaks at 450 and 530 �C, and these

peaks could be attributed to phase changes in mineral

matter at higher temperatures. Better monitoring of phase

changes would be observed at higher temperatures

([650 �C) (Wang et al. 2016). TGA of ROS and COS

indicated a 4% mass loss with high stability up to 450 �C.DSC of ROS indicated an endothermic process at

80–100 �C. The main outputs of thermal analysis (Fig. 4a)

were: a) OS was a good source of liquid fuel, which is

Table 2 Ultimate, proximate analysis, and oil content of OS and

other residues

Parameter OS ROS COS

Ultimate analysis (%)a

C 23.10 14.22 5.33

H 2.61 0.82 0.83

N 0.47 0.12 ndb

S 3.48 3.28 0.67

Proximate analysis (%)c

Moisture 3.1 1.5 0.5

Ash 41.7 52.6 73.6

Volatile matter 15.4 10.4 1.4

Fixed carbon 39.8 35.5 24.5

Oil and ash assay (%)d

Oil 19.82 4.7 0.4

Spent 73.2 87.8 94.72

a Measured by GC analysis (Al-Degs et al. 2012)b nd: not detectedc According to standard method (ASTM D3172 2013): moisture

content: heating at 105 �C for 2 h using an electrical oven. Volatile

content: heating at 525 �C for 7 min in muffle furnace. Fixed carbon:

heating at 800 oC for 3 h in muffle furnace. Ash con-

tent % = 100-moisture (%)-volatile (%)-Fixed C (%)d As outlined in the literature (Al-Alla and Nassef 2015)


123

easily pyrolyzed at 350–400 C under atmospheric condi-

tions, and b) ROS and COS were thermally stable up to

500 �C and hence would be utilized as ingredients in

construction materials (Fig. 4b, c).

IR measurements were useful for detection of the

organic and inorganic moieties. The IR spectra of oil shale

and other processed forms are depicted in Fig. 5.

For oil shale, the following IR bands were appeared in

good intensities: 2922, 2852, 2509, 1415, 1032, and

873 cm-1. Moreover, overlapping bands were appeared

over the spectral range 797–466 cm-1. IR bands observed

at 2992 and 2852 cm-1 were attributed to the symmetric

and asymmetric stretching vibrations of aliphatic CH2 in

kerogen (Kumar et al. 2013). The low intensity of these

peaks reflected the low content of oil in the sample. The

sharp peaks positioned at 1415 and 873 cm-1 indicate the

presence of calcite in large amounts. In fact, the influence

of temperature on kerogen removal or destruction was

evidenced from the absence of 2922 and 2852 cm-1 peaks

in the IR spectra of COS and ROS (Fig. 5). Moreover, the

intense influence of temperature on calcite was also evi-

denced from the lower intensity of 1415 cm-1 peak in

COS compared with ROS. The sharp peak positioned at

466 cm-1 indicated the presence of Si/Al minerals, and the

high intensity of this peak in COS also reflected the

resistance of these minerals against temperature. The IR

peaks appeared at 1032 cm-1 indicated the presence of

pyrite in the samples (Kumar et al. 2013). The peaks at

797, 779, and 772 cm-1 were observed in all samples with

higher intensities in COS (Fig. 5), indicating the presence

of large fraction of inorganic moiety in the matrix.

Particle size distribution and possible utilization

as construction materials and in geopolymers

Due to the high contents of Ca, Si, and Al in ROS and

COS, such residues could be used as active ingredients in

construction materials, precursors for geopolymer, and as

solid adsorbents (Sarkar et al. 2005, 2006). To assess the

convenient industrial application, particle size distribution

of COS and ROS was measured by laser technology, and

the final results are provided in Fig. 6.

As shown in Fig. 6, particle size range of ROS was

within range 4.0–129.0 lm. Moreover, finer particles were

observed for COS with a range of 3.3–85.0 lm. For more

assessment of size ranges and industrial applications, D10,

D50, and D90 were estimated as outlined in the literature

(Al-Degs et al. 2014). For ROS, the value of D10 was

33.5 lm, and this indicated that 10% of the particles have

diameter 33.5 lm and less. The corresponding D values for

ROS were D10 = 33.5 lm, D50 = 65.4 lm, and

D90 = 98.8 lm. For COS, the results were

D10 = 21.5 lm, D50 = 41.5 lm, and D90 = 73.4 lm. The

earlier values indicated that 90% of collected ROS particles

have diameter of 98.8 lm or less, while it was 73.4 lm for

COS particles. In fact, the fine nature of COS particles was

mainly attributed to the harsh burning conditions as the

process was accomplished at 750 oC in the presence of O2

gas. For both solid wastes, particle size ranges were within

Fig. 4 TG and DSC curves for OS (a), ROS (b) and COS (c).Heating rate at 5 �C/min and under atmospheric conditions


123

the typical size of atmospheric aerosol 0.01–100 lm(Sarkar et al. 2006), and then, disposal of such materials

was not recommended. As already known, particle size

range can indicate the proper utilization of solid residues

(Sarkar et al. 2005, 2006). Solid residues of diameter less

than 10 lm were often recommended as ingredients in

construction materials, while larger particles (45–100 lm)

were preferable as filters or solid adsorbents (Al-Degs et al.

2014). For ROS and COS, the average diameters were 66.0

and 45.0 lm, respectively. Accordingly, both solids could

not be utilized as ingredients in construction materials as

the average diameters were much higher than 10 lm.

Moreover, using both residues as precursor for geopolymer

was not possible as Si/Al ratio of both residues was sig-

nificantly higher than 3.0 (Pandey et al. 2012). Based on

the earlier discussion, the best utilization for ROS and COS

would be as solid adsorbent or as filters in gas purification

systems.

Efficiency of different solvents for heavy metals

extraction

Different solvents were tested for extraction of metals from

OS and other solid wastes. The tested solvents were known

Fig. 5 IR spectra of oil shale

and other solid residues


123

of their high efficiency toward metals extraction from solid

residues (Kosson et al. 2002). The overall results along

with TCLT are provided in Table 3.

In OS, extraction efficiency of most metals (provided in

%) was rather low for all solvents. Even HNO3 did not

exhibit its common extraction power for heavy metals.

Using HNO3, %extraction was ranged from 6.3 (for Ca) to

43.4 (for K) as indicated in Table 3. At basic and neutral

conditions, extraction of most metals was not high (\42%)

and extraction of Ca and K by NaOH was not even

achieved. Comparatively, extraction of heavy metals (Ni,

Cr, V, Co, and Cu) was notably higher using NaCl with

extraction range 24.8–42.6%. The high extraction of metals

by NaCl would indicate that heavy metals were attached

with mineral moiety of OS. The interesting point in

Table 3 was that OS is not a toxic material on aquatic

environment. The earlier conclusion was deduced from the

modest extraction of all cations (6.8–34.6%) as supported

by TCLT. United States Environmental Protection Agency

(USEPA) was regulated the upper limits of many leachable

heavy metals from solid residues (USEPA 1996). Table 3

lists the final level of toxic metals from OS by TCLT. The

maximum concentration was observed for Co and Cu with

levels of 41.0 ppm and 50.9 ppm, respectively. Indeed, the

elution of metals was not high when compared with the

safe limits which set at 100 ppm for most metals (USEPA

1996). In fact, the modest extraction of heavy metals was

attributed to following two reasons: a) the presence of high

level of organic matter, which may retard the direct contact

with aqueous extractant. Moreover, strong interaction of

heavy metals with organic matter is highly possible, which

retard their extraction, and b) the strong interaction of

heavy metals with the inorganic moiety of OS, and this

would retard their simple liquid extraction.

Fig. 6 Particle size distribution

of solid residues


123

Undoubtedly, a better extraction of metals from ROS

and COS by all solvents was observed. As indicated in

Table 3 for ROS, the best elution was achieved by HNO3

with %extraction of 62 (for Cu) to 96.7 (for Cr). It was

interesting to notice the better extraction of Ca (up to 80%

using HNO3) from ROS compared to OS. Both H2O and

NaCl solutions outperformed NaOH for metals elution,

which reflected the oxidized nature of metals in the matrix.

Upon oil extraction, the final residue becomes more

hydrophilic, and this would help for better contact with

aqueous solvents and hence better extraction. In fact, the

release of heavy metals was substantially higher than in

OS, and this would make ROS as a toxic solid residue. For

better environmental assessment of ROS, the amounts of

leached metals were checked against regulated levels. The

results indicated that the levels of all heavy metals were

exceeded the safe limit (100 ppm). The level of released Cr

was 4.4 times higher than the safe limit, and this would

make direct disposal of ROS is not recommended. In the

meantime, extraction of heavy metals by nitric acid would

be a necessary job before utilizing the spent oil shale as

fertilizer or adsorbent for water purification. Finally, better

extraction of all metals was observed for COS (Table 3).

The best elution was observed for HNO3, 66% (for V) and

93% (for Na). Based on TCLT, COS was rather of less

toxicity than ROS as the final level of metals did not

exceed the safe 100-ppm level. The poor extraction by

acetic acid may reflect the strong interaction of metals with

the inner matrix that subjected to high temperatures. Based

on leachability tests, ROS could be discharged into envi-

ronment but after elution of toxic heavy metals. More-

over, ROS is a good source of Cr, V, Co and Cu.

As indicated from XRF measurements and extraction

tests, heavy metals were present in variable amounts and

degree of stripping was dependent on the type of residue

and nature of solvent. The majority of metals were eluted

by HNO3. Table 4 summarizes the most suitable conditions

at which the maximum level of the metals would be

attained. The data provided in Table 4 were generated from

Table 3. For example, the maximum content of Na ions

(1927 mg/L) was extracted from COS using HNO3.

The following conclusions could be deduced from

Table 4: a) Natural oil shale was not a good choice for

metals extraction. In fact, the best utilization of natural OS

was to extract oil, and this aim was achieved by simple

liquid extraction or by in situ retorting, b) most metals

(except Ca and V) would be simply extracted from COS

using HNO3, c) the best conditions for V and Ca extraction

would be achieved using ROS and HNO3 as extractant, d)

although most metals would be extracted in high levels,

separation of eluted metals is necessary to get the metals in

their pure states, and e) enrichment factors can explain the

extraction behavior of heavy metals from different resi-

dues. Extraction of Ni, Cr, V, and Cu from their

Table 3 Extraction efficiency of different solvents for metals elutiona

Extractant Na Ca K Ni Cr V Co Cu

OS

HNO3(pH 1.0) 24.5 6.3 43.4 25.8 21.7 15.2 25.8 20.2

H2O 9.5 \1 33.0 16.0 16.2 8.7 12.0 14.8

NaCl 14.3 1.4 35.8 35.1 28.7 24.8 36.5 42.6

NaOH (pH 14.0) 19.2 \1 \1 18.4 8.5 11.2 12.4 12.4

TCLT-test (pH 5.5)b 21.8 6.8 34.6 9.4 (22.3 ppm)c 8.3 (23.0 ppm) 11.7 (24.0 ppm) 25.3 (41.0 ppm) 31.8 (50.9 ppm)

ROS

HNO3(pH 1.0) 72.1 80.8 64.8 61.9 96.7 67.1 64.1 62.0

H2O 63.1 27.6 47.3 47.6 54.5 49.5 45.8 50.2

NaCl 63.9 32.9 39.0 52.4 48.4 53.5 42.0 54.9

NaOH (pH 14.0) 54.1 9.8 20.1 19.0 17.6 13.4 26.7 19.6

TCLT-test (pH 5.5)b 67.2 32.1 60.4 57.1 (120 ppm)c 82.6 (440 ppm) 48.1 (360 ppm) 61.1 (160 ppm) 58.8 (150 ppm)

COS

HNO3(pH 1.0) 93.0 75.0 90.2 92.1 88.2 66.0 77.1 97.3

H2O 43.0 26.4 38.6 55.6 53.9 44.1 33.4 55.9

NaCl 50.3 26.5 40.8 53.2 51.5 36.8 40.0 48.3

NaOH (pH 14.0) 26.8 9.2 31.0 22.8 29.4 33.8 27.7 20.3

TCLT-test (pH 5.5)b 74.3 84.1 59.8 86.4 (15 ppm)c 74.8 (22.8 ppm) 58.8 (\1 ppm) 65.1 (7 ppm) 67.4 (12 ppm)

a The reported results were taken as an average of three trialsb This test stimulates the potential toxicity of a solid waste toward aquatic environment (Al-Degs et al. 2014)c Values in brackets are the concentrations of released metals after extraction


123

corresponding residues is a good example on the impor-

tance of EF. With high EFs (1.7–3.3), Ni, Cr, and Cu were

extracted in large amounts by HNO3 from COS. ROS is a

good source for V as EF of this metal was 37 times higher

compared to its EF in COS. Commercially, ROS is a good

source for V, while COS is a convenient source for Ni, Cr,

Co, and Cu ions. However, separation of heavy metals is

necessary at this stage. Currently, separation of heavy

metals after extraction from processed oil shale is being

investigated in our laboratory.

Practical applications of oil shale and other solid

residues

For better practical applications of oil shale and other

processed forms (ROS and COS), more special tests were

carried out. Thermal properties, textural characteristics, Si/

Al ratio were estimated, and the results are provided in

Table 5.

Beside oil extraction, OS could be utilized as low-grade

fuel for heat production. This conclusion was deduced from

the marked gross heating value (GHV) 5255 kJ/kg. In fact,

direct burning of oil shale would be attractive for certain

small industries; however, emission of SO2 gas in large

amounts would retard its direct application on a large scale.

Moreover, accumulation of S in extracted kerogen is pos-

sible, and more research is necessary at this stage. With a

modest GHV and high inorganic residue, local oil shale is

not economically feasible compared to coal or common

liquid fuel. The GHVs of ROS and COS did not support

their usage for heat production. The interesting point in

Table 5 was the high surface area and porosity of COS

compared to OS. In fact, combustion of OS at 750 �C was

the reason for developing high surface area and porosity

after oil destruction. The bulk density of the materials also

revealed the developed porosity in COS with a value of

0.74 g/mL. It seems that retorting conditions have devel-

oped some porosity in the matrix. It is important to mention

that the inorganic nature of OS played a major role for

developing stable and porous matrix after oil stripping. Si/

Al ratio does not support using any form of OS as precursor

for geopolymer preparation. As already know, the optimum

Si/Al ratio for a precursor should be 3.0 to end up with a

stable geopolymer (Al-Degs et al. 2014). In light of the

earlier discussion, the best application of processed oil

shale is as solid medium for pollutants removal from

solution. It seems that many researchers have reached to

this conclusion (Ibrahim and Jaber 2007; Al-Asheh et al.

2003).

Removal of Pb ions and phenol from solution

The earlier physical tests indicated that ROS and COS have

large particle diameter, large surface area, and developed

porosity and hence would be utilized as solid adsorbent. As

a demonstration for ROS and COS utilization, removal of

two model pollutants from solution was studied. The

selected pollutants were Pb ions and phenol, and both are

problematic pollutants in the aquatic environment. Both

residues were thoroughly washed with 1.0 M HNO3 solu-

tion to remove all metals from the inner matrix and to

activate the surface. The solid surfaces were washed with

Table 4 Maximum levels of

eluted metals from solid

residues at different

experimental parametersa

Metal Level (ppm) Waste EF (ROS/OS)b EF (COS/OS)b Solvent

Na 1927 COS 1.2 1.0 HNO3

Ca 206,400 ROS 0.9 0.9 HNO3

K 5700 COS 1.9 1.8 HNO3

Ni 364 COS 0.9 1.7 HNO3

Cr 720 COS 1.6 2.9 HNO3

V 502 ROS 3.7 0.1 HNO3

Co 251 COS 1.6 2.0 HNO3

Cu 508 COS 1.6 3.3 HNO3

a Data were picked up from Table 3b Enrichment factors were estimated from the results of XRF (Table 1)

Table 5 Textural properties

and calorific (heating values) of

ROS, SOS, and COS

Material GHVa (kJ/kg) SSAb (m2/g) Pore volume Bulk density (g/cm3) Si/Al ratio

OS 5255 1.5 0.03 1.22 12.2

ROS 133 18.2 0.12 0.96 10.1

COS 13 56.4 0.31 0.74 8.9

a Gross heating valueb Specific surface area


123

distilled water before running adsorption tests. For com-

parison purposes, adsorption behavior of pollutants by oil

shale was also investigated. Adsorption isotherms are

depicted in Fig. 7. Adsorption data were presented by

Langmuir and Freundlich isotherms, and all parameters are

provided in Table 6.

For adsorption isotherms, L2-isotherm was obtained for

all systems except Pb adsorption by COS which showed

H-isotherm (Giles and Smith 1974). In L2-isotherm,

removal of Pb and phenol from solution by adsorbents was

attained by forming one layer only (Giles and Smith 1974).

In fact, L2-isotherm reflected the high adsorption affinity

between solutes and solid adsorbents at lower concentra-

tions, however, at higher concentrations the surface satu-

rated with solutes. In H-isotherm, Pb saturated the surface

at lower concentrations. Adsorption isotherms of heavy

metals and charged dye molecules have been reported to

have L2-shape (Giles and Smith 1974). In both cases, L2-

and H-isotherms were reflected the higher affinity of Pb

and phenol compared with solvent molecules (Giles and

Smith 1974). The interesting results obtained from

adsorption tests were: a) OS has rather modest adsorption

for both solutes, and b) a better affinity of phenol toward

ROS and better affinity of Pb toward COS were reported.

To measure the maximum retention values of both solutes

and to study the mechanism of adsorption, adsorption data

were modeled by two common equations. Parameters of

the models and degree-of-fit X2 are provided in Table 6.

In general, Langmuir was applicable for presenting

adsorption behavior of both solutes from solution. For

Langmuir model, X2 values were ranged from 0.9 to 2.5,

and the best result was observed for phenol removal by OS

with a value of 0.9 only. On the other hand, Freundlich

model showed limited application with X2 values 4.5–11.2.

Presenting adsorption behavior of phenol by ROS was not

successful with X2 value of 11.2. Based on Qmax values,

removal trend of Pb by the adsorbents was increasing in the

following order: ROS (0.76 mg/g)\OS (0.91 mg/g)

\COS (2.39). For phenol removal, the following trend

was reported: OS (1.70 mg/g)\COS (2.02 mg/g)\ROS

(3.60 mg/g). The earlier trends indicated that COS was the

best adsorbent for Pb ions while ROS was the best adsor-

bent for phenol uptake from solution. The high affinity of

phenol toward ROS would be attributed to the high surface

area and the presence of some organic matter that improved

hydrophobic interaction with the organic pollutant. The

developed porosity, high surface area and high content of

mineral moiety were positively contributed for Pb removal

by COS. As indicated from KL values, the best affinity was

achieved for Pb adsorption by OS and ROS. The applica-

bility of Langmuir model indicated the homogenous dis-

tribution of active sites on the surfaces, as the model

assumed homogenous active sites for adsorption (Allen

et al. 2004). Although Langmuir model was workable for

presenting Pb and phenol removal from solution, testing of

Freundlich model is still necessary. As given in Table 6,

Freundlich model was not applicable as confirmed by the

high X2 values 4.5–11.2. Although it is not highly appli-

cable for the current adsorption systems, the values of n (-

exponents in Freundlich model) would indicate the

favorable uptake of Pb and phenol by OS and other wastes.

Fig. 7 Adsorption isotherms of phenol and Pb ions by OS (a), ROS(b) and COS (c) at 25 �C


123

As indicated from KF values, the model predicted the same

adsorption trend (as obtained from Langmuir’s model) for

both solutes.

Conclusions

Due to fluctuation in the prices of crude oil, there was a need

to look for another source of energy and oil shalewas the best

choice due to its availability in Jordan. Extraction of oil

and direct combustion of oil shale left large amounts of spent

oil shale rich in Ca. Chemical analysis indicated that the new

discovered OS was rich in carbonate with high ash content.

XRD indicated that calcite and quartz were the main min-

erals inOS,ROS andCOS.Analysis of oil shale indicated the

final level of kerogenwas 19.82% and this value, indeed, was

notably higher than the one reported for El-Lajjun OS. XRF

analysis indicated that Vwas concentrated in ROS compared

with OS and COS. SEM analysis indicated that the tested oil

shale has fossil origin. Particle size distribution indicated

that ROS and COS have fine particle diameters of 66 and

45 lm, respectively and hence the best application should

be as filter or solid adsorbent. The utilization of Ca-rich ROS

and Ca-rich COS as fertilizer is possible but after removing

toxic heavy metals like Cr, Co, V, and Zn. Based on TCLT,

OS was not a toxic by-product as the level of eluted metals

was less than the safe limit recommended by international

agencies. However, both ROS and COS would be toxic

residues due to the high levels of elutedmetals. Gross heating

value of OS was rather high which support its application as

low-grade fuel. Surface area, pore volume, and apparent

density all indicating the development of porous surfaces in

COS and ROS which generated under the effect of high

temperature. Accordingly, the best utilization for both sur-

faces was as solid adsorbent. The removal of Pb ions and

phenol from solutionwas tested using ROS andCOS. Phenol

was favorably removed by ROS, while Pb was favorably

removed by COS.

Acknowledgements This research was financially supported by the

Deanship of Graduate Studies at the Hashemite University. The kind

donation of oil shale samples by JOSCO was highly appreciated.

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Characterization and utilization of solid residues