Abstract
The purpose of this work was to study the effect of chemical surface properties of
activated carbons for their use in water purification. To achieve this objective,
activated carbon in both granular and powdered forms namely: as received and
devolatilized carbons were prepared. Proximate analysis of the carbon materials
was performed. Mass titration experiments were carried out to determine the point
of zero charge of the activated carbon materials. Again, using an ultraviolet
spectrophotometer, the adsorption of phenol on as-received and devolatilized
activated carbon was investigated. Adsorption isotherms were acquired from which
the monolayer adsorption capacities were calculated.
1.1 ORIGIN AND NATURE OF ACTIVATED CARBON
Carbon is the fifteenth most abundant element in the earth’s crust and the fourth
most abundant element in the universe by mass after hydrogen, helium and
oxygen. Scientists, industries, and consumers use different forms of carbon and
carbon containing compounds in many ways such as activated carbon or carbon in
its active form which can be used to purify water, among others.
Activated carbon is a form of carbon that has been produced to make it extremely
porous and thus have a very large surface area available for adsorption or chemical
reactions.
It can be defined as a microcrystalline non-graphitic amorphous form of carbon
which has been processed to develop a high internal porosity due to its network of
inter-connecting pores.
The history of activated carbon is dated since the fifteenth century, during the
time of Columbus when sailors used to blacken the inside of wooden water barrels
with fire, since they observed that the water would stay fresh much longer. It is
likely that people at that time proceeded by intuition only without having any
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insight into the mechanism of the effect. The mechanism was recognized
beginning from the eighteenth century.
In 1862, Lipscombe prepared a carbon material for purifying portable water. This
development paved the way for the commercial application of activated carbon
first for portable water and then in waste water sector.
1.2 METHODS OF MANUFACTURE OF ACTIVATED CARBON
The methods employed in the industrial manufacture of activated carbons are
numerous but consist of three main methods namely; Chemical activation, Steam
activation and thermal processing techniques.
The raw materials or precursors used in the manufacture of activated carbon are as
follows; Softwood, coconut shell, lignite, hardwood, grain and agro products,
bituminous coal, anthracite, etc.
Chemical activation is generally used for the production of activated carbon from
sawdust, wood or peat and uses chemicals for activation. Chemical activation
technique involves mixing an inorganic chemical compound with the carbonaceous
raw materials and the most widely used activating agents are Phosphoric acid and
Zinc Chloride.
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Steam activation technique is generally used for coal-based, coconut shell and
grain-based activated carbons and uses gases, vapors or a mixture of both for its
activation.
Thermal processing technique is a separation process that removes unwanted
materials from the carbonaceous precursor used under varying heat applications.
This technique is at a lower cost compared to the two techniques above and meets
all environmental standards, while others need expensive solutions to achieve the
same results.
1.3 NEED FOR PRESENT INVESTIGATION
The need for present investigation of this material cannot be over emphasized. This
is as a result of the pressing need for treatment of waste water emanating from
domestic and industrial concerns.
Activated carbon plays an important role in the purification of fluids (water),
including vegetable oils used in domestic cooking and as a precursor in industrial
manufacture of food products. The slow pace of technological development in the
country has resulted to the expenditure of the nation’s resources on importation of
activated carbons to meet the demand for local chemical and process industries, as
well as the demand for municipal and industrial water treatment plants.
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Rapid industrialization, together with the increase in modern methods of
agriculture and the increase in population, has contributed to the pollution of the
ecosystem. Most of the pollutants are toxic to living organisms. It is therefore
imperative that waste water has to be treated to remove the toxic materials before
disposal to the environment. Most methods of treating water have some inherent
shortfalls. Activated carbon treatment was therefore developed because of its
effectiveness in pollutants removal, especially in water purification.
1.4 OBJECTIVES AND SCOPE OF THE STUDY
The primary objectives and scope of the present investigation include the
following:
i. Acquisition of the different types of activated carbons available to the nation’s
chemical industry.
ii. Modification of the surface physical and chemical properties of the carbon
material, for their use in liquid phase applications.
iii. Determination of the physical properties of the as-received and modified
activated carbon materials.
iv. Testing the adsorption capacity of the carbon materials in adsorption processes.
v. Evaluation of the fractional surface coverage for each carbon material.
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vi. Proposal of a scheme for the optimal modification of activated carbon material
for optimal application in liquid phase adsorption.