NGC2010 Carbonaceous shale by UGK6U5j

VIEWS: 59 PAGES: 11

									Physico-chemical behavior of carbonaceous shale at Batu Gajah, Perak: Their
                          troubles and mitigation
  Askury Abd Kadir, Angga Pratama Herman, Aminur Rashid Mohd Shariai and Aaron
                                 Subash George

                                          ABSTRACT

The Paleozoic carbonaceous shale exposed around Batu Gajah is interbedded with sandstone and
siltstone, which is sandwiched in between Kinta Limestone over a total thickness estimated to be
about 3,000m. It deposited within deep marine environment indicated by the dissemination of
reduction pyrite. The exposures along Seputeh-Batu Gajah (new road) were studied whenever
numbers of slope failure occurred along the stretch, as well as stained road surfaces and drains,
which is believed trigger by the material properties of black shale. Chemical weathering is the
only factor that contributes to the change of chemical and physical properties of the
carbonaceous shale. Acid rock drainage (ARD) is one of the environmental problem occurred
and it produced by the oxidation of sulphides minerals, such as pyrite and marcasite (FeS2). Both
of these phenomena can affect the physical and chemical properties of the carbonaceous shale.
Acid Rock Drainage is found around the world both as a result of naturally occurring processes
and activities associated with land disturbance such as highway construction and mining where
acid-forming minerals exposed to the air and water. These acidic can cause metal in geologic
material to dissolve, which can cause a very serious contamination and damage the environment
for the flora and fauna around the area. Acidic soil contributed by pyrite oxidation in
carbonaceous shale has a very low pH near 3. An appropriate method need to be implemented in
order to treat the acidic soil problem. Due to the high acidity, plants or vegetation are unable to
grow. The growth of plants or vegetation is important because the roots of the plant can serve as
natural fiber reinforcement and will increase the resistance to slope failures. Pyrite oxidation,
also referred to as pyrite disease or pyrite decay, is identified by a sulphuric acid odor, white
crystalline powder, yellow sulphide powder, and/or gray to yellowish microcrystalline mass in
and out of specimens. One of the important approaches to prevent pyrite oxidation is to create a
surface coating on pyrite. In the study conducted, a coating of iron 8–hydroxyquinoline was
formed by leaching pyrite with a 0.10M H2O2/0.0034 M 8-hydroxyquinoline solution; stability of
the coated pyrite was tested under various pH and temperature conditions. It shown the iron 8-
hydroxyquinoline coating could significantly suppress further pyrite oxidation by both chemical
(H2O2) and biological (Thiobacillus ferrooxidans). Ammonium gas and ethanolamine
thioglycollate treatments neutralize sulphuric acid and remove ferros-sulphate, and are reportedly
effective in partly or completely removing oxidation reaction products. Calcium carbonate or
limestone powder can also be utilized to treat the ARD, where the exposed black shale covers by
calcium carbonate, and then cover back by layer of softwood and hardwood. These mitigation
methods suggested can be implemented to enhance the growth of grass and stabilize slopes.

Introduction

       This project is about to determine the physical properties of the carbonaceous shale that
can be found along Seputeh – Batu Gajah road. Along this road, there were some environmental
issues at the left and the right side of the road. Due to the construction of the new road, the
carbonaceous shale is exposing to the atmosphere when the hill is excavated during this process.
        Due to the exposure to the environment and atmosphere, the carbonaceous shale can
cause rock weathering and also Acid Rock Drainage. Rock weathering happens naturally while
acid rock drainage is produced by the oxidation of sulphides minerals such as pyrite and
marcasite (FeS2). Both of these phenomenons can affect the physical and chemical properties of
the carbonaceous shale.
This black shale can cause the acid rock drainage (ARD). Acid rock drainage is produced when
sulphide-bearing rocks and mine waste minerals such as pyrite (FeS2) and pyrrhotite (Fe1-xS) are
exposed to water and atmospheric oxygen (Keith 1992). The mixture may react via chemical
and/or biological oxidation processes to form sulphuric acid which, together other metal
hydroxides and heavy metal products can contaminate soils and pollute surface and ground water
resources. Increased soil and water acidity and heavy metal contamination has very serious and
damaging environmental ramifications for flora and fauna.

Acidic soil contributed by carbonaceous shale is basically due to pyrite oxidation. Pyrite (FeS2)
is a common mineral found in sedimentary rock and fossils, and its decay is a major problem in
the conservation of fossil specimens. Pyrite oxidation, also referred to as pyrite disease or pyrite
decay, is identified by a sulphuric acid odor, white crystalline powder, yellow sulphide powder,
and/or gray to yellowish microcrystalline mass in and out of specimens.
The carbonaceous shale experience weathering and acid rock drainage due to the exposure to the
environment and it affect the surrounding area such as ‘soil cancer’ and land slide.

Problem statements

       Carbonaceous shale generally strong in nature, however due to the construction of the
Seputeh - Batu Gajah new road, the carbonaceous shale were expose to the surface because of
the hill excavation during the construction. The exposure to the water and atmospheric oxygen
can cause the properties of the carbonaceous shale along the Seputeh – Batu Gajah new road
changed.
       This acidic condition can cause metals in geologic material to dissolve, which can affect
ground water quality and also can lead to what known as ‘soil cancer’. As a result, the
carbonaceous shale that initially is black in colour will change to rusty brown and this acidic
condition will prevent the growth of plants around the area. This phenomenon can affect the
strength of the soils and also lead to landslide and other land problems
       The exposed carbonaceous shale also experience rock weathering and it indicates that the
grass can grow at the weathered shale. Since the rock weathering takes some time to occur, the
land structure or the exposed carbonaceous shale that affected by the ARD earlier are weak and
exposed the area to the environmental issues as stated earlier. The project is about to indicate the
Physical and Chemical properties of the carbonaceous shale of fresh to weathered sample in
order to determine cause of the environmental issues happens at the area.
Acid Rock Drainage is low pH ground and surface waters generated by the oxidation of the
sulfide minerals to produce sulphuric acid. The process occurs naturally, but it can be caused or
made worse by exposes sulphide-bearing rocks to air. Poor environmental practices can cause
ARD. The major problem with ARD is that acidic waters dissolve metals, which in certain
quantities are harmful to aquatic life and humans.


If the rock at the site contains sulfide minerals such as pyrite (FeS2), then it could generate ARD
when exposed to oxygen and water. The sulphur will react with oxygen with the help of bacteria
(Thiobacillus ferroxidans) to form sulfuric acid. When the rock oxidizes, they change colour to
rusty brown, and the waters will show a drop in pH. From the figure1 and 2, all the green stuff at
the site will be died due to the acidic soil.
Acidic soil contributed by pyrite oxidation in carbonaceous shale has a very low pH near 3. An
appropriate method need to be implemented in order to treat the acidic soil problem. Due to the
high acidity, plants or vegetation are unable to grow. The growth of plants or vegetation is
important because the roots of the plant can serve as natural fiber reinforcement and will increase
the resistance to slope failures.
Objective

      To determine the physical and chemical properties of carbonaceous shale for fresh and
       weathered sample.

      Compared and analysed the results obtain with the reference data and determine the by-
       product of the carbonaceous shale after ARD and weathering.

              1. To analyze the chemical contain in the black shale and the effects expose to
                 the environment.
              2. To identify the mechanisms for controlling the oxidation of black shale.
              3. To plan the remedial actions again the problem.

              4. To find the most effective method to prevent rapid pyrite oxidation or to
                 suppress pyrite oxidation chemically or biologically.
              5. To find an appropriate treatment to treat acidic soil
              6. To conduct few experiments to find the appropriate plantation that can grow
                 on a acidic soil condition
Physical and chemical behavior
       the density of the carbonaceous shale decreases as it weathered because of the weathering
and the effect of the ARD.
The carbonaceous shale colour are initially dark in colour gradually becomes lighter as the
carbonaceous shale experience weathering and ARD. The weathering and ARD phenomenon
also affected the physical condition of the shale which initially the carbonaceous shale is hard
becomes more brittle and porous.

CHNS experiment results proof that the carbon content inside the carbonaceous shale decrease
significantly as the rock weathered. The theory also supported by the colour test results where
the carbonaceous shale colour becomes lighter as the rock experience weathering.




                      (a)                                               (b)
                        (c)                                                (d)

Figure …: The CHNS distribution with accordance to weathering grades. SPOT1- Fresh;
SPOT2- Slightly weathered; SPOT3 – Moderately weathered; SPOT4 – Highly weathered;
SPOT5 – Completely weathered; SPOT6 – Residual soil.

       The carbon percentages of the fresh carbonaceous shale are initially 6.885% and as the
carbonaceous shale experience weathering, the percentages of the carbon are decreasing as in
table 10 and almost depleted at spot 4. The carbon increase again at spot 5 and 6 but the
percentage of the carbon at spot 5 and spot 6 are very low.
       As the carbonaceous shale is exposed to the atmosphere and water, the carbonaceous
shale experience chemical weathering where in figure 10, the carbon content inside the
carbonaceous shale is decreasing. The carbon react with oxygen, water and pressure to produce
oxidized residuum and also soluble compound [8].
       The hydrogen content of the carbonaceous shale is increasing as shown in figure 11 but
the increasing of the hydrogen is not significant or in the other words, the results are more or less
the same. From the result obtain in table 9, the percentage of hydrogen is range from 0.4% to
0.8% which means the hydrogen content in the carbonaceous shale are not effected much by
either weathering or acid rock drainage.
       The nitrogen shows in figure 12 is decreasing in trend lines as the nitrogen in the
carbonaceous shale decrease from spot 1 to spot 6. From results table 9 shows the highest
percentage of nitrogen is 0.343% and the lowest is 0.162% which means the hydrogen does not
severely affected by the weathering and also acid rock drainage.
       Sulphur is one of the main elements that involve in the acid rock drainage. Sulphur can
react with iron in presence of oxygen and water to produce hydrogen ions, acidity, sulphate ions
and soluble metal ions in the ARD [4]. This is the reason why is the percentage of sulphur in the
carbonaceous shale are decreasing.
the percentage of carbon, hydrogen, nitrogen and sulphur successfully determined. It is found
that the percentage of carbon significantly decreased and almost depleted at the end of the
weathering profile. The percentage of sulphur also gradually decreased as the rock weathered
due to ARD and heavily affected the area surround the carbonaceous shale.
        The XRD results are successfully determine the mineral constituent of the carbonaceous
shale samples. The minerals contain in the carbonaceous shale are quartz and clay minerals such
as kaolinite and montmorillonite.




Figure ….: The XRD output for fresh carbonaceous shale.
Figure ..: Surface morphology of fresh shale showing flaky flakes of clay minerals.

       The surface morphology of carbonaceous shale changes due to the effect of the
weathering and acid rock drainage. It is found that, the fresh carbonaceous shale has some
‘flaky’ effect which indicates the organic content inside the shale. As the shale weathered, the
morphology of the carbonaceous shale does not have ‘flaky’ effect and becomes more pores. It
can conclude that, the weathering and ARD can cause the surface morphology of the
carbonaceous shale change.

Acid Rock Drainage

From the past years study, the acid rock drainage (ARD) is one of the biggest issues for
environment throughout the last decade. The study had been conducted regarding this big issue
and found that there are several factors that could lead this problem happen. The three major
factors are oxygen from atmosphere, water from rain or underground source and last factor is the
rock in this case, the black shale. When the three elements are meeting the formation of the acid
rock drainage could be happen and the process is natural.
There have been various studies on the mechanism of ARD formation. The reactions describe
and present in 3 stages (Kleinmenn et al., 1993).
Stage 1 involves the relatively slow chemical or biochemical oxidation of pyrite and other sulfide
minerals near-neutral pH according to Eqn (1).
                       2FeS2(s) + 7O2 + 2H2O → 2Fe2+ + 4SO2- + 4H+ (1)
This initial step might be catalyzed by acidophilic microorganisms, such as Thiobacillus
ferrooxidans, through direct contact with sulfide minerals. As acid begins to accumulate around
the minerals as indicated in Eqn (1), the process enters stage 2.


In stage 2, ferrous iron is oxidized to ferric iron (Eqn 2), which precipitates as ferric hydroxide
(Eqn 3) and releases more acidity.
                              4Fe2+ + 4H+ + O2 → 4Fe3+ + 2H2O (2)
                             Fe3+ + 3H2O → Fe (OH)3(s) + 3H+ (3)
As the pH falls even further, below about 3.5, some ferric iron remains in solution to oxidize
additional pyrite directly according to Eqn (4).
                    FeS2(s) + 14Fe3+ + 8H2O → 15Fe2+ + 2SO4+ + 16H+ (4)
In stage 3, the associated acidophilic bacteria rapidly catalyzes the process by oxidizing more
ferrous iron to ferric iron (Eqn 5) and the overall rate of acid production is increased by several
orders of magnitude. This stage will produces large quantities of acids associated with the release
of heavy metals into solution. At this stage, acid rock drainage becomes a problem.
                                     Fe2+ + O2 (aq) → Fe3+ (5)
                                Fe3+ + FeS2(s) → Fe2+ + SO4+ (6)
ARD

The acid rock drainage (ARD) is one of the biggest issues for environment throughout the last
decade. Black shale is typically very fine-grained and contain pyrite, phosphate, and abnormally
large amounts of heavy metals. Pyrite (FeS2) that is available at the black shale is the major
element that can be directed to the formation of the ARD. Pyrite is containing iron and sulfur
mineral, when it exposed to the atmosphere it could be formation the change of the iron. The
process happened when The oxidation of the sulfide to sulfate soluble the ferrous iron (iron(II)),
which is next oxidized to be ferric iron (iron(III)). When this happened, it will flow the yellow
liquid which is iron (III) from the rock to the environment that was containing acid to the
environment.
The oxidation process of the pyrite happens when the rock is exposing to the atmosphere. In this
case, the construction of the new road at Batu Gajah, had cut of the hill to give the new road
being construct at the middle of the hill. The specific role of acidophilic chemoautotrophic
bacteria in pyrite oxidation thru the research is become controversy matter. Since oxidation of
FeS2 may proceed slowly by chemical routes, it had been suggested that microorganisms are not
important to ARD formations. Their role has been suggested as direct catalyst that alters the
overall the chemical reaction rates or as specific catalyst agent which alters the rate of
intermediate reaction. It is suggested that the microorganism remove electron from the surface
pyritic iron to start reaction and/or catalyst sulfur oxidation or they simply increase iron(III)
concentration. Thiobacillus are colorless, rod-shaped, Gram-negative bacteria with polar flagella.
They possess an iron oxidize, which allows them to metabolize metal ions such as ferrous iron
(Baker RA.1970): Thiobacillus are strictly aerobic bacteria. All species are respiratory
organisms. Thiobacillus are obligate autotrophic organisms, meaning they require inorganic
molecules as an electron donor and inorganic carbon (such as carbon dioxide) as a source. They
obtain nutrients by oxidizing iron and sulfur with O2.




Figure 4: Image of the Thiobacillus. ferrooxidans (Sci-Tech Encyclopaedi, 2009)

Due to pyrite oxidation, not only the soil becomes acidic but the soil is decomposed. Plants or
vegetation are not able to grow. This is when slope failures occur. The resistance and the strength
of the soil can be reinforced by the plant root system. In order to have a plant root system, the pH
of the soil need to increased to make it less acidic in order for plants or vegetation to grow.



Conclusion
the physical properties of the carbonaceous shale change due to weathering and ARD. The
density of the carbonaceous shale decreases from fresh to weathered sample as a result of the
decomposition of carbon from the carbonaceous shale. The colour of the shale also changes
which initially dark gradually decreased becomes lighter as the shale weathered.
CHNS elemental analysis, it is found that the percentage of carbon gradually decreased and
almost depleted at weathered sample which also affected the colour of the carbonaceous shale.

								
To top