Diatomite: Its Characterization, Modifications and Applications
Hossam Elden Galal Morsy Mohamed Bakr
The review tackles common diatomite, its characterization, modifications and its composites, heavy metal toxicity and its immobilization techniques using diatomite, other important applications of diatomite.
January 14, 2010; Accepted: March 30, 2010;
Published: June 05, 2010
Diatomite rock is a loose, earthy or loosely cemented porous and lightweight
rock of sedimentary origin, mainly formed by fragments of armor (skeletons)
of diatom algae: diatomea and radiolaria. Diatomite is a microscopic diatom
alga whose size ranges from 0.75 to 1500 m; sometimes this rock is called infusorial
earth, kieselguhr, or mountain meal. The main components of the siliceous armor
are silica hydrates of a different degree of water content (opals) SiO2
_nH2O. Diatomite rock belongs to the group of silica-bearing materials.
Diatomite has its origin from a siliceous, sedimentary rock consisting principally
of the fossilized skeletal remains of diatom, a unicellular aquatic plant related
to the algae, during the tertiary and quaternary periods (Paschen,
1986; Arik, 2003).
Diatomites (or kieselguhrs) are mineral deposits of diatomaceous algae, those
commercially exploited being restricted to a relatively modem age, starting
from the Miocene. Older deposits have suffered tectonic processes, bringing
about modifications of the texture and crystalline phase of the mineral. Amorphous
silica, a constituent of the diatom frustulae, is the main component of diatomite,
although variable quantities of other materials (metal oxides, clays, salts
(mainly carbonates) and organic matter) may also be present, chemical precipitation
and atmospheric contact, together with the prevailing environmental conditions,
are determinant factors in the nature and importance of the impurity content
of a deposit (Mendioroz et al., 1989).
Diatomite is a natural material formed from the remains of diatoms, which grew
and were deposited in seas or lakes. Diatomite products are used in a variety
of ways, such as reinforcing, stiffening and hardening of organic solids, reducing
adhesion between solid surfaces, increasing adhesion, increasing viscosity,
surfactant effects, hydrophobic effects, absorbent, catalysts and cloud seeding
(Zhaolun et al., 2005).
Diatomite is abundant in many areas of the world and has unique physical characteristics,
such as high permeability (0.1-10 mD) and porosity (35-65%) (Murer
and Mobil, 2000), small particle size, low thermal conductivity and density
(Hassan et al., 1999) and high surface area (Gao
et al., 2005). The properties of diatomites surface, such as
hydrophobia, solubility, charge, acidity, ion exchange and adsorption capabilities,
are highly governed by the presence of water, which is partially structurally
connected to the crystal mesh of the diatomite, forming active hydroxyl groups
on it (Yuan et al., 1997).
Diatomite (SiO2_nH2O) or diatomaceous earth is a pale-colored,
soft, lightweight sedimentary rock composed principally of silica microfossils
of aquatic unicellular algae. Diatomite consists of a wide variety of shape
and sized diatoms, typically 10-200 mm, in a structure containing up to 80-90%
voids (Lemonas, 1997). Diatomites highly porous
structure, low density and high surface area resulted in a number of industrial
applications as filtration media for various beverages and inorganic and organic
chemicals as well as an adsorbent for per liter and oil spills. Although, diatomite
has a unique combination of physical and chemical properties, its use as an
adsorbent in wastewater treatment has not been greatly investigated (Aytas
et al., 1999; Michell and Atkinson, 1991).
CHARACTERIZATION OF DIATOMITE
Bliznakov and Gocheva (1978) and Robertson
(1980) studied diatomites by IR spectroscopy and Differential Thermal Analysis
(DTA) and revealed that amorphous silicon dioxide is the main component of the
diatomite. Water adsorbed on the diatomite surface and hydrated water bound
to divalent cations are released at temperatures of 110-180°C and insignificant
amounts of water are released at 800°C. However, the authors did not report
the types of hydroxyl groups on the diatomite surface and data on the change
in the band positions with a variation in the temperature for calcined samples.
The dehydration of diatomites, water loss and the influence of the pore structure
on the dehydration were not investigated. Castro et al.
(1979) studied the pore structure by porosimetry; however, they did not
investigate the change in the pore structure after acid treatment and calcination.
Mendioroz et al. (1989) made reports on a thermogravimetric
study of 12 samples of different diatomite deposits from S and SE Spain. Thermogravimetric
proved to be an efficient and rapid method for mineral diagnosis, the shapes
of the TG curves giving the carbonate and silica contents of the diatomite samples
Structural investigation of some important Chinese diatomites done by Wang
et al. (2009) and discussed The IR spectra exhibit bands associated
with the Si-O and Al-O bonds. The acid treatment and calcination lead to a change
in the size, size distribution and structure of pores. Fuya
et al. (1995) reported that, Diatomite samples taken from the Leizhou
Peninsula have been studied by chemical analysis, DTA, TG, XRD, IR, SEM and
X-ray Energy Spectroscopy. The study shows that the diatomaceous genera and
species and their organic contents are variable with buried depth, from Melosira
to Stephanodiscus and then to Cyclotella. Various impurities in the samples,
such as quartz, kaolinite and montmorilonite indicate different sedimentary
Diatomaceous silica, pretreated at various temperatures between 125 and 900°C
was subjected to dissolution experiments and was analyzed using X-ray diffraction
and infrared spectra (Kamatani, 1974).
The IR spectrometry is a useful measure to study surface hydroxyl groups. However,
it is difficult to distinguish different surface hydroxyl species of diatomite
because the O-H vibration frequency (ca. 3745 cm-1) of surface isolated
hydroxyl groups and H-bonded hydroxyl groups are analogical. On the other hand,
diatomite prefers to adsorb water for its high porosity, thereby in IR spectra
the peak of strongly H-bonded hydroxyl groups is overlapped by the broad peak
(with middle wave number at (ca. 3500 cm-1) that assigned to the
adsorbed water and then is difficult to be discerned (Yuan
et al., 2001).
The IR spectroscopy has proved to be a powerful method to identify the isolated
and H-bonded hydroxyl groups on the surface of synthetic silica (Iler,
1979; Bergna, 1994). Frost and
Johansson (1998) proposed that diffuse reflectance infrared Fourier transform
spectroscopy (DRIFT) is more applicable than transmission infrared spectroscopy
for powder samples because it provides a rapid technique for analyzing samples
without any interference through sample preparation and the technique is particularly
suitable for the study on the hydroxyl stretching region of silicate minerals.
Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT), Raman spectroscopy
of adsorbed Pyridine molecules (Py-Raman) and in situ Py-IR have been used Yuan
et al. (1997) to investigate the hydroxyl species and acid sites
on diatomite surfaces. In our study Elaboration and characterization of natural
diatomite (raw material) in Aktyubinsk/Kazakhstan has been investigated including
the structure, mineralogical specifics and chemical composition (Mohamedbakr
and Burkitbaev, 2009a).
DIATOMITE MODIFICATIONS AND ITS COMPOSITES
There are several methods to modify the surface characteristics of diatomite
for various purposes. The diatomite purification in HCl and the diatomite calcination
(Goren et al., 2002; Khraisheh
et al., 2005) have been applied to make diatomite more inert for
using the treated diatomite as filter support. In these processes, the disappearance
of the OH groups on the diatomite surface has a detrimental effect on the surface
area. Khraisheh et al. (2004a) modified diatomite
by NaOH treatment and manganese oxide deposition to improve the adsorption capacity
of the diatomite for removal of heavy metals like Pb2+, Cu2+
and Cd2+ from wastewater. Their modified diatomite has the
surface area of 80 m2 g-1 and the adsorption capacity
of 99.00 mg Pb2+/g, 55.56 mg Cu2+/g and 27.86 mg Cd2+/g,
respectively and they explained that manganese oxide and its blockage of pores
of diatomite played an important role in the adsorption on the heavy metals.
Another modified diatomite with lime and aluminum sulfate is utilized to remove
P from wastewater (Wu et al., 2005). This modification
might result in aluminum hydroxyl groups transplanted onto the surface of diatomite
and elevated removal of Phosphorus primarily via chemisorption. Total Phosphorus
(TP) was reduced from 5.2 mg L-1 in influent to 0.55 mg Lin-1
treated effluent and 80%TP removal efficiency was obtained by the addition of
chemically modified diatomite.
Ferrihydrite-modified diatomite was developed and characterized by Xiong
et al. (2009) and Xiong and Peng (2008) as
a novel and effective P, ferrihydrite-modified diatomite has a BET specific
surface area of 211 m2 g-1 and has a P adsorption capacity
of 37.3 mg P/g. Ferrihydrite-modified diatomite was formed through the deposition
of Si-containing ferrihydrite into pores of diatomite. And they studied the
effects of process parameters such as concentrations of FeCl2, NaOH
and drying temperature on the formation mechanism and chemical characteristics
of ferrihydrite- modified diatomite are studied by using X-ray absorption near-edge
structure spectroscopy. The spectra were recorded in total electron yield mode
and/or fluorescence yield mode to investigate the chemical nature of Fe and
Si on the surface and/or in the bulk of ferrihydrite-modified diatomite, respectively.
It was found that only the surface SiO2 was partially dissolved in
the NaOH solution with stirring and heating, whereas the bulk of diatomite seemed
to be preserved. The dissolved Si was incorporated into the structure of ferrihydrite
to form the 2-line Si-containing ferrihydrite on the surface of diatomite. The
crystalline degree of ferrihydrite increased with the increasing FeCl2
concentration and the Brunauer-Emmett-Teller specific surface area of ferrihydrite-modified
diatomite decreased with the increasing FeCl2 concentration. The
crystalline degree of ferrihydrite decreased with the increase of NaOH concentration.
The high temperature calcination caused an energy shift in the Si L-edge spectra
to the high energy side and a transformation of Si-containing ferrihydrite to
crystallized hematite might occur when ferrihydrite-modified diatomite is calcined
at 900°C. In this study, the optimal synthesis conditions for the ferrihydrite-modified
diatomite with the least crystalline Si-containing ferrihydrite and the highest
surface area were found to be as the follows: 0.5 M FeCl2 solution,
6 M NaOH solution and drying temperature of 50°C. Synthetic 2-line Si-containing
ferrihydrite was prepared by following the procedure of Seehra
et al. (2004) 0.025 M Na2SiO3.9H2O
solution was added to 0.1 M Fe(NO)3.9H2O solution to yield
the molar ratio of Si/(Si + Fe) = 0.2. Ammonium hydroxide was then slowly added
to this solution to bring the pH to 10. The precipitate was filtrated and washed
by distilled water and then dried at 50°C in an oven.
New Inorganic Composite Materials (ICM) were prepared (Hadjar
et al., 2008) by mixing an Algerian natural diatomite with a charcoal
from pine. After using two consecutive necessary procedures of treatments, the
ICM were characterized in order to reveal their properties with the aid of different
techniques of analysis. The preliminary obtained results have clearly shown
that the important quantity of calcium carbonates present in natural diatomite
have disappeared from the new ICM after heating and chemical attack.
Grigoryan et al. (2008) synthesized calcium
hydrosilicate from Armenian diatomite and β-cristobalite obtained from
diatomite and calcium hydroxide under hydrothermal conditions. They established
the optimal process parameters.
Ibanez and Sandoval (1998) investigated the synthesis
of calcium hydromonosilicate from Spanish diatomite and calcium hydroxide. It
is established that, during hydrothermal synthesis, to obtain CSH that contains
no Ca (OH)2, an experimental duration longer than 4 h and a temperature
of 180°C are required. For Armenian diatomites, an experimental duration
of 1-3 h and temperature of 90-98°C were suggested, with the use of sodium
or potassium hydroxidesas mineralizers.
Grigoryan et al. (1997, 2007)
established that the use of γ-tridymite and β-cristobalite instead
of β-quartz in the hydrothermal autoclave synthesis of calcium hydromonosilicate
allows one to obtain calcium hydromonosilicate at comparatively low temperatures
and durations of the experiment omitting the intermediate phase. And they proved
that the process of cristobalization of diatomite starts at 1050°C. In investigations,
they also used β -cristobalite obtained from Armenian diatomite.
Hsien et al. (2009) prepared diatomite-TiO2
composite for photo degradation of Bisphenol-A in water. and they found that
the photo catalytic activity in the degradation of Bisphenol-A on diatomite-TiO2
composites can be better than on pure TiO2 powders possibly due to
more BPA molecules adsorbed and enriched on the modified TiO2 particles.
Bazhal et al. (1975) showed that the surface
modification of diatomite by Ca(II), Al(III) and Sn(IV) ions resulted in an
increased filtration rate since these cations have a high coagulation capacity
which give a marked aggregation of the particle. Hence, it can be said that
the modification by manganese oxides has changed the colloid-chemical properties
of diatomite and increased the aggregation of the particles, which resulted
in a higher filtration rate. Moore and Reid (1973) reported
an increase in filtration rates for acrylic fibers after modification with manganese
Ediz et al. (2010) examined the calcination
and filtration characteristics of diatomite. For this purpose, diatomite ore
was calcined at 1000°C in order to improve the material characteristics
for use in filtration. The physical, chemical, thermal and micro-structural
features of the raw and the calcined diatomites were then determined to compare
them with those of the commercial filter aids currently used. In order to determine
filtration efficiency of the diatomite samples, several filtration tests were
carried out together with the beer samples and the commercial filter aids taken
from a leading beer factory in Turkey. It is shown that the calcined diatomite
could successfully be used for beer filtration after suitable arrangement of
the particle size distribution, such that the highest possible flow rate and
filtrate clarity are obtained.
We used FT-IR (Mohamedbakr et al., 2009) spectroscopy
in the regime of total internal reflection studied the reaction products of
amorphous calcium phosphate, containing both mono-and diphosphate in the molar
ratio of 7/3 and consisting of 80% water, with the surface of diatomite particles-a
natural mineral sediment dioxide-based silicon aktobe field. It is shown that
the main chemical bonds in the products of interaction as distinct from those
ones in the original phosphate and minerals. When the dehydration reaction products
behave like most amorphous phosphate and the chemical bonds PO alter their strength,
reflecting a loss of moisture and the formation of pores in which the adsorbed
DIATOMITE AND HEAVY METALS REMOVAL AND WATER PURIFICATION
In recent decades, water pollution phenomena have become more and more frequent and acute. Petroleum hydrocarbons represent one of the most common categories of groundwater pollutants that are found at many contaminated sites, making surface water and/or groundwater unsuitable for many uses (including drinking), due to their toxic and/or carcinogenic properties.
Water is considered an important and scarce commodity in many countries around the world. In particular, the contamination of surface and ground water with heavy metals is a concern. Industries such as plating, ceramics, glass, mining and battery manufacturing are considered the main source of heavy metals, e.g., lead, in local water streams. The elevated level of lead and other heavy metals, e.g., cadmium, chromium and mercury, in the local water streams is a major concern to public health.
Inorganic pollutants, in particular heavy metal ions, constitute a major class
of water contaminants. Most heavy metals are known to be toxic and carcinogenic
agents and, when discharged in wastewater, represent a serious threat to the
human population. Currently, many industries use heavy metals in the processing
of raw materials and consequently, discharge of such metals into aquatic bodies
and sources of drinking water has begun to be strictly controlled (Dantas
et al., 2001). Lead, cadmium and zinc are regarded as major contaminants.
Lead and its compounds play an important role in industrial activities including
the manufacture of paint, storage batteries and leaded gasoline. Cadmium and
zinc are used as protective coatings for iron and steel. Cadmium enters the
system primarily through absorption in the large intestine and is de-posited
in the liver and kidneys (Holliday and Park, 1998). Most
zinc compounds have no toxic properties, but zinc chloride is highly corrosive
to the skin, eye and respiratory tract.
Over the last few decades, adsorption has gained importance as an effective
purification and separation technique used in wastewater treatment (Lazaridis
et al., 2003). Adsorption systems are rapidly gaining prominence
as treatment processes which produce good quality water containing a low concentration
of dissolved organic and inorganic compounds (Walker and
Weatherley, 1999). Sorption technologies, including physical and chemical
adsorption and ion-exchange, have the potential to treat water and industrial
The removal of heavy metals from industrial waste water is considered an important
application of adsorption processes using a suitable adsorbent (Al-Qodah,
2000). There is growing interest in using low-cost, commercially available
material for adsorption of heavy metals. Jordan has large deposits of diatomaceous
earth and as a result, research is being undertaken to assess its feasibility
as a low-cost alternative to activated carbon.
Within literature, many treatment processes have been proposed for the removal
of heavy metals. Chemical precipitation, membrane filtration, ion exchange,
alum coagulation and activated carbon adsorption are some of the most commonly
used methods for the treatment and disposal, of metal-containing wastes (Orhan
and Buyukgungor, 1993; Yadava et al., 1991).
Adsorption is considered to be a particularly competitive and effective process
for the removal of trace quantities of heavy metals (Huang
and Blankenship, 1984). In principle, any solid material with a microporous
structure can be used as an adsorbent, e.g., bone and coal char, clays, iron
oxides, synthetic and natural zeolites, molecular sieves and activated carbon.
The most important property of any adsorbent is the surface area and structure.
Furthermore, the chemical nature and polarity of the adsorbent surface can influence
the attractive forces between the adsorbent and adsorbate. The highly developed
structure of activated carbon allows wide usage as an adsorption media for a
large number of organic and inorganic materials, including trace concentrations
of heavy metals. Activated carbon, however, is not suitable in developing countries
due to the high costs associated with production and regeneration (Panday
et al., 1985). The use of alternative low cost materials for heavy
metals removal is required. Materials like activated peat and clay (Brown
et al., 2000; Fischer, 2002), chitin and
chitosan (Rae and Gibb, 2003; Bassi
et al., 2000) have been tested as potential sorbents for heavy metal
removal. A comprehensive review has been presented by Bailey
et al. (1999).
Karthikeyan and Chaudhuri (1986) studied the removal
of Hg(II) by coal. After chemical treatment by nitric acid oxidation, H2O2
oxidation, CS2 sulphurisation and impregnation with manganese oxides,
the authors reported that the efficiency of the treated coal exceeded that of
activated carbon. Ground husks modified with EDTA have also shown a high efficiency
for removal of Cd(II) and Pb(II) (Okieimen et al.,
1991). Brandao and Galembeck (1990) also reported
that the impregnation of cellulose acetates with manganese dioxide resulted
in high removal efficiency of Cu(II), Pb(II) and Zn(II) from aqueous solutions.
Sagara et al. (1989) prepared a selective ion-exchanger
material for Li(I) and Na(I) by dispersing MnO2 within cellulose
The removal of BTEX (benzene, toluene, ethyl-benzene and xylenes) and MTBE
(methyl tertiary butyl ether) from aqueous solution by diatomite raw (DR) and
thermally modified diatomite at 550, 750 and 950°C was studied by Aivalioti
et al. (2010).
Diatomite has already been used for the adsorption of different elements and
substances from water and wastewaters, either in its natural form (raw) or modified
(chemically or thermally), presenting very promising and positive results. Ridha
et al. (1998) described first the determination of the physico-chemical
characteristics and the surface properties of a natural Moroccan low density
silicate from the diatomites family. Then, the adsorption of aqueous Ag+
ions on this diatomite and the Langmuir model are studied.
We studied the removal uranium from the liquid waste by using diatomite as
an adsorption medium. This is important because natural diatomite is an abundant
and low-cost material when compared to other artificial chemicals. In this study,
the removal of uranium from aqueous solutions by natural/modified diatomite
earth from (Aktyubinsk /Kazakhstan) has been investigated. A comparison in Uranium
adsorption was investigated between natural diatomite and three modified diatomite
by calcinations and acidification by 0.5 N HCl (D, D_HCl, D_900 and D_900_HCl).
The adsorption of uranium on the chosen diatomite sample was examined as a function
of uranium concentration, contact time and type of diatomite used (Mohamedbakr
and Burkitbaev, 2009b).
Naturally occurring diatomaceous earth (diatomite) has been tested by Al-Degs
et al. (2001) as a potential sorbent for Pb(II) ions. The intrinsic
exchange properties were further improved by modification with manganese oxides.
Modified adsorbent (referred to as Mn-diatomite) showed a higher tendency for
adsorbing lead ions from solution at pH 4. The high performance exhibited by
Mn-diatomite was attributed to increased surface area and higher negative surface
charge after modification. Scanning electron microscope pictures revealed a
birnessite structure of manganese oxides, which was featured by a plate-like-crystal
structure. Diatomite filtration quality was improved after modification by manganese
oxides. Good filtration qualities combined with high exchange capacity emphasized
the potential use of Mn-diatomite in filtration.
On the spot of using an abundant and low-cost material in lead removal from
the liquid waste, we studied (Mohamedbakr and Burkitbaev,
2008), lead solutions were treated using diatomite and, as a result of the
treatment, its concentrations were reduced depending on the type of diatomite
used and type of treatment which effect on the lead uptake capacity. The relative
adsorption capacities of lead ions onto diatomite samples followed the sequence:
D>D-HCl>D-900>D-900-HCl. The sorption of Pb2+ from aqueous
solutions by a range of adsorbents.
Computerized flow injection coupled with potentiometric stripping analysis
(Al-Ghouti et al., 2004) (FIPSA) was employed
for examination of the adsorption behavior of Pb(II), Cd(II) and Zn(II) ions
onto diatomite modified with manganese oxides. Signal optimization was undertaken
with respect to flow rate, deposition time, deposition potential, oxidizing
agent concentration, thickness of mercury film, solution pH and metal ion concentration.
Examination of the column adsorption characteristics was facilitated by introduction
of an adsorption micro column, as a complementary component of the flow injection
system. The resulting breakthrough curves were employed to calculate parameters
including adsorption capacity and adsorption rate constant, taking into consideration
initial ion concentration, flow rate, mass and particle size of adsorbent and
column internal diameter. Adsorption capacities, determined using the Thomas
mathematical model, showed that manganese modified Jordanian diatomite had an
efficiency towards the removal of heavy metal ions from aqueous solutions; Cd(II)
> Zn(II)Pb(II). The relative adsorption rates of the ions followed
the order: Pb(II) > Zn(II)Cd(II).
Fe-Mn binary oxide has been homogeneously incorporated into diatomite and exhibited
high As(III) removal efficiency (Chang et al., 2009).
The oxidation of As(III) can significantly enhance the As(III) removal efficiency
and reduce the As(III) toxicity. Acid solution and high temperature are advantageous
to oxidize and adsorb As(III). Electrostatic attraction and specific adsorption
were the two major forces during the As(III) adsorption process. Being different
from other coexisting anions, the presence of silicate and phosphate has negative
effects on the As(III) adsorption. With the increase of pH, the negative influence
of silicate was enhanced, while the competition ability of phosphate for the
adsorption sites was weakened. Because of the high oxidation ability and adsorption
capacity for As(III), FMBO-diatomite can be filled into fixed beds for large-scale
water treatments, in order to remove As(III) with low concentration from water
rapidly and effectively.
Chu et al. (2010) investigated the feasibility
of treating micro-polluted surface water for drinking water production with
a bio-diatomite dynamic membrane reactor (BDDMR) at lab-scale in continuous-flow
mode. Results indicate that the BDDMR was effective in removing CODMn,
DOC, UV254, NH3-N and trihalomethanes formation potential (THMFP)
at a hydraulic retention time (HRT) of 3.5 h due to its high concentrations
of Mixed Liquor Suspended Solids (MLSS) and Mixed Liquor Volatile Suspended
Solids (MLVSS). The removal of pollutants was mainly ascribed to microbial degradation
in BDDMR because the dynamic membrane alone was much less effective in pollutant
removal. Though the diatomite particles (5-20 mm) were much smaller in size
than the aperture of the stainless steel support mesh (74 mm), microorganisms
and their extracellular polymer substances could bind these particles tightly
to form bio-diatomite particles which were completely retained by the support
mesh. The analysis of Molecular Weight (MW) distribution by Gel Permeation Chromatography
(GPC) shows that the BDDMR could effectively remove the hydrophilic fraction
of dissolved organic materials present in the raw water.
Processed diatomite possesses an unusual particulate structure and chemical
stability that lends itself to applications not filled by any other form of
silica. Foremost among these applications is its use as a filter aid, which
accounts for over half of its current consumption. Its unique diatom structure,
low bulk density, high absorptive capacity, high surface area and relatively
low abrasion are attributes responsible for its utility as a functional filler
and as an extender in paint, It is actively exploited and used as raw material
for filtration of fluids, pesticides, thermal treatment, paper and rubber filling,
natural water purification, among others. From the analytical point of view,
this substrate has been mainly applied as chromatographic columns, Paper, rubber,
an in plastics and thermal insulating material; polish, abrasive to name a few
representative applications (Frederic and Kadey, 1983;
Aruntas et al., 1998; Arik
et al., 2002).
Diatoms are well-known for their versatility as indicators of past environments
and climates (Stoermer and Smol, 1999) but their application
to sediment provenance studies, although used with some success (Pokras,
1991; Abrantes et al., 2007) is not common
worldwide. In Lake Tutira for example, diatoms have been useful for differentiating
between sedimentary units derived entirely from catchment erosion and those
derived predominantly from within-lake and lake margin sources (Orpin
et al., 2006). One implication of the Lake Tutira study is that diatoms
could be a useful tool to identify sediment sources in parts of the Waipaoa
sedimentary system and may be an important compliment to carbon, radiochemical
or biogenic marker studies. Furthermore, a quantitative measure of the diatom
concentrations for background terrigenous sedimentation fluxes offshore could
offer another means to identify high-delivery events caused by floods, storms
Crucial to the use and accurate interpretation of diatom assemblages is an
understanding of their individual ecological preferences. Surface sediments
are often used to document modern diatom distribution patterns. These in turn
are used to create a template in relation to present-day environmental variables
so that similar patterns observed in fossil samples can be more accurately interpreted.
Although much is known of the modern ecological preferences of diatoms from
surface sediment and modern analogue studies around the world, only a few such
studies have been undertaken in New Zealand (Cochran, 2002;
Reid, 2005) and no diatom transfer functions have been
developed in New Zealand's marine realm. Therefore, as a first step towards
providing quantitative and locally calibrated diatom studies for source-to-sink
research, we aim to document the species preserved in surface sediments offshore
of New Zealand and investigate the factors determining their distribution (Cochran
and Neil, 2010).
Kieselguhr sludge can be effectively utilized in the fabrication of calcium
silicate bricks and to what extent the kieselguhr sludge plays a role in the
reaction mechanisms of the hardening process. Furthermore, the influence of
carbonation on calcium silicate bricks produced using kieselguhr sludge was
investigated (Russ et al., 2006).
In the San Joaquin Valley, CA, diatomite is the uppermost productive member
of the Monterey formation. Initial oil saturations vary from 30 to 65% and total
oil accumulations in diatomite are estimated to be at least 10-12 billion barrels
original oil in place (Ilderton et al., 1996).
Oil-bearing diatomite layers are interbedded among shale and mudstone layers
(Schwartz, 1988). Individual layers vary in thickness
from a few centimeters to several meters and the gross thickness of these layers
can exceed 330 m_1000 ft. The interbedding of diatomaceous rock and shale resulted
from cyclicrseasonal deposition of diatoms, mud and silt and the subsequent
consolidation of diatom fragments and grains of mudrsilt. Thus, the quality
of diatomite varies from layer to layer and field to field. In some cases, diatomite
is water wet and has a matrix that is almost entirely biogenic silica with very
little clay. In others, the rock might be mixed wet and clay content can be
relatively high. A described later, they choose to begin with and characterize
relatively clean diatomite.s
We used diatomite as catalytic matrix (Mohamedbakr et
al., 2010) that we synthesized Polyethylene glycol-400 (PEG-400) grafted
in diatomite support as macromolecule ligand and the structure of the ligand
was characterized by IR spectroscopy. The complex of silica-supported PEG-400
and paldium [shortened form, SiO2-PEG-Pd (II)], radium [shortened
form, SiO2-PEG- Rh (II)], iron [shortened form, SiO2-PEG-
Fe (II)] were for the first time synthesized and characterized by infrared spectroscopy
and transmission electron microscope. The possible structure of the complex
was discussed. As a catalyst, complexes were used in oxidation process of cyclohexene
and its catalytic activity and selectivity was also investigated. Experimental
results showed that the complex possessed activity and selectivity for epoxidation
of cyclohexene. The analysis oepoxycyclohexane was done by gas chromatography.
In addition to natural fractures that may be cemented or uncemented, wells
in diatomite are hydraulically fractured to improve well productivity and injectivity.
Induced fractures are massive with heights on the order of 100 m and total lengths
of roughly the same magnitude. Such fractures are used for water (Patzek,
1992) and steam injection (Kovscek et al., 1996a,
b), as well as production.
A systematic investigation of fluid flow characteristics within diatomite_a
high porosity, low permeability and siliceous rock is reported by Akin
et al. (2000). Using an X-ray computerized tomography_CT. scanner
and a novel, CT-compatible imbibition cell, they studied spontaneous cocurrent
water imbibition into diatomite samples. Air-water and oil-water systems are
used and the initial water saturation is variable. Mercury porosimetry and a
scanning electron microscope_SEM. are employed to describe diatomite pore structure
and the rock framework. Diatomite exhibits a fine pore structure and significant
pore-level roughness relative to sandstone thereby aiding the flow of imbibing
water. Despite a marked difference in permeability and porosity as compared
to sandstone, they found similar trends in saturation profiles and dimensionless
weight gain vs. time functions. Although diatomite is roughly 100 times less
permeable than sandstone, capillary forces result in a strong imbibition potential
for water such that imbibition rates rival and surpass those for sandstone.
Diatomite, as an adsorbent, can effectively remove the basic dye from solution
and is inexpensive (Khraisheh et al., 2004b).
The capability of diatomite to remove reactive dyes from aqueous solution is
less efficient compared to activated carbon. In addition, when diatomite is
directly used in wastewater treatment, there are some limitations, especially
in column studies, especially in relation to low filtration rate. Al-Ghouti
et al. (2005) showed that MOMD is a much more effective adsorbent
for the removal of basic and reactive dyes from aqueous solutions. As a result,
in this study, MOMD was used as the main adsorbent. It has also been shown that
MOMD has a high selectivity for dye removal. The effect of initial concentration,
particle size, mass of the adsorbent, pH and agitation speed on adsorption behavior
of Methylene Blue (MB) onto Jordanian diatomite has been investigated (Al-Ghouti
et al., 2009). The maximum adsorption capacity, q, increased from
75 to 105 mg g-1 when pH of the dye solution increased from 4 to
11. It is clear that the ionisable charge sites on the diatomite surface increased
when pH increased from 4 to 11. When the solution pH was above the pHZPC,
the diatomite surface had a negative charge, while at low pH (pH<5.4) it
has a positive charge. The adsorption capacity increased from 88.6 to 143.3
mg g-1 as the initial MB concentrations increased from 89.6 to 225.2
mg dm-3. The experimental results were also applied to the pseudo-first
and -second order kinetic models. It is noticed that the whole experimental
data of MB adsorption onto diatomite did not follow the pseudo-first order model
and had low correlation coefficients (R2<0.3). The calculated
adsorption capacity, qe,cal, values obtained from pseudo-first order kinetic
model did not give acceptable values, qe,exp. The maximum uptake capacity seems
to be independent of the particle size of the diatomite when the particle size
distribution is less than 250-500 m. While at larger particle size 250-500 m,
the maximum uptake capacity was dependent on the particle size. It would imply
that the MB adsorption is limited by the external surface and that intra particle
diffusion is reduced. The effect of the agitation speeds on the removal of MB
from aqueous solution using the diatomite is quite low. The MB removal increased
from 43 to 100% when mass of the diatomite increased from 0.3 to 1.7 g.
The use of diatomite as a partial replacement for cement in the production
of cement mortar was investigated by Degirmenci and Yilmaz
(2009). Diatomite was used at 0, 5, 10 and 15% replacement by weight for
cement while sand and water quantities were kept constant. Compressive and flexural
strength, freeze-thaw resistance, sulfate resistance, water absorption and dry
unit weight of the mortars were determined. The compressive and flexural strength
decreased with increasing diatomite content for all curing periods. However,
the compressive strength of the cement mortar which was produced with 5% diatomite
content complied with the minimum specified value of given in the standards.
Diatomite replacement generally increased the compressive strength of the cement
mortar after 25 freezing and thawing cycles. Water absorption of the mortars
decreased with the increase of diatomite content except the mortar containing
of 15% diatomite. Dry unit weight of the cement mortar was lower than the control
mortar because of high porosity of diatomite. The expansion of the cement mortar
bars immersed in 5% sodium sulfate solution decreased with increasing diatomite
content and generally the sulfate resistance of the mortars was higher than
that of the control mortar.
Diatomite is used as pozzolanic additives for Portland cement and mortars and
grouts. Aydin and Gu (2007) studied the effect of diatomite
as additive on the properties of concrete. They indicate that the increase of
additive ratio results a sudden decrease in compressive strength. The pozzolanic
reaction of diatomite leads to the formation of higher amounts of hydrate products,
especially at the age of 28 days (Kastis et al.,
2006). Stamatakis et al. (2003) demonstrated
that the use of diatomite rocks as cement additives has drawbacks such as higher
water demand, but compressive strength of the laboratory produced cements exhibit
higher values than that of the reference Portland cement. This diatomite rock
had the greatest amount of silica content reflecting its high opal-A content.
Fragoulis et al. (2005) investigated that the
addition of diatomite in cement results an increase of its specific surface
(Blaine) because of their high grind ability.
The adsorption of some textile dyes by diatomite was investigated using Sıf
Blau BRF (SB), Everzol Brill Red 3BS (EBR) and Int Yellow 5GF (IY). Adsorption
of these textile dyes onto diatomite earth samples was studied (Erdem,
2005) by batch adsorption techniques at 30°C. The adsorption behavior
of textile dyes on diatomite samples was investigated using a UVvis
spectrophotometric technique. The effect of particle size of diatomite, diatomite
concentration, the effect of initial dye concentrations and shaking time on
adsorption was investigated. Adsorption coverage over the surface of diatomite
was studied using two well-known isotherm models: Langmuirs and Freundlichs.
These results suggested that the dye uptake process mediated by diatomite has
a potential for large-scale treatment of textile mill discharges. According
to the equilibrium studies, the selectivity sequence can be given as IY>SB>EBR.
Values of the removal efficiency of the dyes ranged from 28.60 to 99.23%. These
results show that natural diatomite holds great potential to remove textile
dyes from wastewater.
We report the formation of vertical carbon nanotubes utilizing diatomite as
a substrate. This new material combines the advantages of carbon nanotubes and
diatomite in one material. The SEM investigations showed that the average diameter
of the carbon nanotubes was 60 nm and the growth was through the tip growth
mechanism. Raman spectroscopy was also used for the carbon nanotubes characterization
and showed two intensive peaks around 1350 and 1580 cm-1 and several
peaks at low frequency range from 100 to 500 cm-1 which are assigned
to the Radial Breathing Mode (RBM) and used as a characteristic of single wall
carbon nanotubes. The photoluminescence measurements at the room temperature
showed two very narrow intensive overlapping peaks near the ultraviolet range
at energy of about 3 eV. And there are two peaks with lower intensity in the
infrared region at 830 nm and at 940 nm (or 1.49, 1.3 eV, respectively) (Duraia
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