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I.1 BACKGROUND
I.1.1 MAN AND METALS
Energy, metals and agriculture are considered to be three major classes of
commodities. The 21st
century is marked as the century of commodities (1)
because it
has long been recognized that these factors have flowed together to create the
unexpected development of civilization. They have so much impact on today‟s life
that they are stated as essential building blocks of the global economy. But, there is
probably no material that has shaped the progress of mankind more than metals. For
ages, metals have faithfully served humanity in all its endeavors to unravel the
mysteries of nature and build powerful machines and installations.
Many years of experience in using metals means that today there is a lot of knowledge
concerning how metals can be used and tailored in order to become optimal materials.
Moreover, it has been observed that, societies that have mastered the production of
metals have been able to thrive and survive. Seeing today‟s scenario it can be truly
said that “We are all addicted to metals”. Man is so much surrounded by metals that
life without metals has become inconceivable.
I.1.2 NEED FOR SEPARATION TECHNIQUES
With millions of uses in day-to-day life and in industries, metals have compelled man
to explore them. To meet the increasing demand for metals, enormous quantities of
metal ores are extracted from the earth‟s crust each year. As the primary sources of
metals and natural ores are steadily getting depleted, the role of recycling in the
production of metals continues to grow (2)
. The flow-cycle of metals in the society
have been thoroughly studied and hence the main emphasis of researchers has been to
evaluate resources, unlock the value in alternative ores, improve process performance
and minimize production costs at all stages of processing from mineralogical analysis
to final applications.
This has raised the requirement for better separation and estimation techniques and
scientists are always in search of speedier and thriftier analytical methods.
Furthermore, methods which are comparatively more selective and rapid are always
the methods of choice for an analyst. It has been observed that many of the domains
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are benefited to a greater extent when these separation methods are aided with
quantification of elements of interest. In practice, however, the analysis is often
complicated by interferences among sample constituents and hence chemical
separations become mandatory to isolate the analyte or remove interfering
constituents. Some common separation methods are precipitation, distillation, solvent
extraction, electrophoresis and various hyphenated techniques.
I.1.3 CHOICE OF ANALYTICAL METHOD
The choice of analytical method depends on a number of factors like speed, cost,
accuracy, convenience, available equipment, number of samples, size of sample,
nature of sample and expected concentration. These factors are interrelated and any
final choice of analytical method involves compromises. It is impossible to specify a
single best method to carry out a given analysis in all laboratories under all conditions
because every method has its own significance and so also do the gravimetric
methods.
The analysis of any complex matrices like rocks, ores, soils, metallurgical and other
inorganic samples, etc. plead for classical methods of separation for the removal of
other interfering sample constituents before these samples are introduced into the
sophisticated instruments. Therefore successful analysis of such samples always
demands for the mutual approach of classical methods with hyphenated techniques.
The advantage of gravimetry is that it is accurate and precise. Also, it is an absolute
method. One of the most important applications is the analysis of standards used for
the testing and calibration of those instrumental techniques which one may consider to
have replaced gravimetry. This application alone justifies the need for gravimetry.
But on the other hand, there are a few problems associated with the practice of
gravimetry. Its disadvantage is that they are generally time-consuming. Also, some of
the precipitating reagents lack in selectivity and so these precipitants may precipitate
more than one ion, unless great care is exercised.
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I.2 MOTIVATION
With a view to respond to the challenges faced in gravimetric analysis, an attempt has
been made in the present investigation to develop new gravimetric methods which are
more rapid and selective for the separation and estimation of nickel(II), cobalt(II) and
zinc(II) employing an organic chelating agent. The application of these developed
methods in various complex matrices has also been included. But it is beyond the
scope of this study to resolve all these issues once and for all.
Not surprisingly, the study of development of new methods can be called for any of
the known elements. But this thesis deals specifically with three elements, viz. nickel,
cobalt and zinc. It is the potential usage of these three elements for the widespread
practical applications which provides the motivation for their selection. Moreover, the
incessant hunt for better methods which can bestow an advantage to the existing
methods sets the foundation of the thesis.
Today, the interest of society gets dragged apparently for exploring those metals that
are capable of generating significant returns to the global economy. The significance
of any metal is completely dependent on their applications which make our lives
sustainable. Today we care more and more about sustainability and yet we seem to
know less and less about the materials that contribute to a sustainable future.
These metals are endowed with unique characteristics and offer good usage potential
and hence the present work aims at the development of new, rapid and selective
methods for the separation and estimation of these elements. The following discussion
endeavors to raise the curtain on how nickel, cobalt and zinc have contributed for the
sustainable development of our society and further assures that these metals will have
an important role to play for years to come.
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I.2.1 NICKEL
Symbol : Ni
Atomic number : 28
Atomic mass : 58.69
Family : Group 10 (VIIIB), Transition metal
Electronic configuration : 1s2 2s
2 2p
6 3s
2 3p
6 3d
8 4s
2
Figure I-I: POSITION OF NICKEL, COBALT AND ZINC IN
PERIODIC TABLE
Adapted from Printable Periodic Table of the Elements, Retrieved March 14, 2013, from
http://chemistry.about.com/od/periodictableelements/a/printperiodic.htm. Copyright 2012 by
About.com. Chemistry. Reprinted with permission.
DISCOVERY AND NAMING
The study of metals was difficult for the early chemists. Many metals looked very
similar. They also acted very much like each other chemically. Nickel was one of the
metals about which there was much confusion.
Nickel is the only element named after the devil. The name comes from the German
word Kupfernickel, meaning "Old Nick's copper," a term used by German miners.
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They tried to remove copper from an ore that looked like copper ore, but they were
unsuccessful. Instead of copper, they got slag, a useless mass of earthy material. The
miners believed the devil ("Old Nick") was playing a trick on them. So they called the
fake copper ore or Old Nick's copper.
Swedish mineralogist Axel Fredrik Cronstedt (1722-65) was the first person to realize
that nickel was a new element (3)
. In 1751, he was given a new mineral from a cobalt
mine near the town of Halgsingland, Sweden. While Cronstedt thought the ore might
contain cobalt or copper, his tests produced a surprising result. He found something in
the mineral that did not act like cobalt, copper, or any other known element. Cronstedt
announced that he had found a new element. He used a shortened version of
Kupfernickel for the name of the new element. He called it nickel.
OCCURRENCE
On Earth, nickel occurs most often in combination with sulfur and iron in Pentlandite,
with sulfur in Millerite, with arsenic in the mineral Nickeline and with arsenic
and sulfur in Nickel Galena. Nickel is commonly found in iron meteorites as the
alloys Kamacite and Taenite.
The bulk of the nickel mined comes from two types of ore deposits. The first
are Laterites where the principal ore minerals are Nickeliferous Limonite:
(Fe, Ni)O(OH) and Garnierite (a hydrous nickel silicate): (Ni, Mg)3Si2O5(OH)4. The
second are magmatic sulfide deposits where the principal ore mineral is Pentlandite:
(Ni, Fe)9S8.
ISOTOPES AND OXIDATION STATES
Naturally occurring nickel is composed of 5 stable isotopes; 58
Ni, 60
Ni, 61
Ni, 62
Ni and
64Ni with
58Ni being the most abundant (68.07% natural abundance). 18 radioisotopes
have been characterized. The most common oxidation state of nickel is +2.
PHYSICAL AND CHEMICAL PROPERTIES
Nickel is a silvery-white metal. It has the shiny surface common to most metals and is
both ductile and malleable. Its melting point is 1455 °C and its boiling point is about
2913 °C. The density of nickel is 8.90 g/cm3. The unit cell of Ni is a face centered
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cube. It is ferromagnetic at room temperature and is readily deposited by
electroplating.
Figure I-II: CRYSTAL STRUCTURE OF NICKEL
Adapted from Crystal structure, Retrieved December 4, 2012, from http://www.oocities.org.html.
Copyright 2012 by Michael Pohs Homepage. Reprinted with permission.
Nickel can resist corrosion by alkalis and confers ductility. It forms alloys readily and
exhibits catalytic behavior. Nickel is a relatively unreactive element. At room
temperature, it does not combine with oxygen or water or dissolve in most acids. At
higher temperatures, it becomes more active. For example, nickel burns in oxygen to
form nickel oxide (NiO). In its familiar compounds nickel is bivalent, although it
assumes other valencies. It also forms a number of complex compounds. Most nickel
compounds are blue or green.
COMPLEXES OF Ni(II)
Nickel(II) commonly forms complexes with three different geometries: octahedral,
tetrahedral and square planar. Some five-coordinate complexes are also known but
are rare. Nickel(II) is a 3d8 system, so octahedral and tetrahedral complexes will have
2 unpaired electrons and square planar complexes usually will have none.
BIOLOGICAL ROLE:
Many but not all hydrogenases contain Ni(II) in addition to iron-sulphur clusters.
Ni(II) centres are common in those hydrogenases whose function is to oxidize rather
than evolve hydrogen. The nickel centre appears to undergo changes in oxidation state
and evidence has been presented that the nickel centre might be the active site of these
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enzymes. A nickel tetrapyrrole coenzyme is present in the methyl reductase and in
methanogenic bacteria.
TOXICOLOGY AND HEALTH
Although Ni(II) is an essential element for animal nutrition, the physiological role of
nickel is not yet established. Pathological alterations of nickel metabolism are
recognized in several human diseases (3)
. The diverse toxicity includes acute
pneumonitis from inhalation of nickel carbonyl, chronic rhinitis and sinusitis from
inhalation of nickel aerosols, cancers of nasal cavities and lungs in nickel workers and
dermatitis and other hypersensitive reactions from cutaneous and parenteral exposures
to nickel alloys.
USES OF NICKEL
Nickel is an unsung metal, yet it plays many vital roles in modern applications.
Nickel-containing materials make major contributions to many aspects of modern life,
but these often go unrecognized. The following discussion will highlight in a clear
and simple way the most important applications of nickel and explores how these
applications contribute to innovation and sustainability in our daily lives (4)
. The chart
below shows the end uses of nickel.
Figure I-III: END USES OF NICKEL
Adapted from Horizonte Minerals, Retrieved February 24, 2013, from http://horizonteminerals.com/nickel_faq/ Copyright 2012 by Horizonte Minerals Plc. Reprinted with
permission.
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60% of all nickel is used to make stainless steel. The modern society is highly
dependent on the stainless steel for the architectural designs of the buildings and for
the infrastructural purposes. That‟s because this material is extremely strong, resistant
to corrosion, easy to form into different shapes, and aesthetically pleasing. Perhaps,
best of all, nickel-containing stainless steel typically contains 60% recycled
material (5)
.
Nickel exists normally in many of the things we eat and drink. Nuts, chocolate,
apricots, beer, tea and coffee naturally contain small quantities of nickel (6)
. Studies
suggest that as a micronutrient the presence of nickel inside the body helps to
maintain balanced calcium levels in muscles and bones (7)
.
The Nickel Development Institute has stated that the combination of corrosion
resistance, cleanability (8)
, ease of fabrication, appearance and availability means that
nickel-containing stainless steels are the materials of choice (9)
for many hygienic
applications in food processing, beverage production, medicine and domestic kitchen
equipment and utensils (10)
.
It also assists in staying healthy. All „surgical stainless steel tools‟ surely has nickel in
it. These intricate instruments require stringent sterilization and cleaning. Nickel-
containing stainless steel can withstand these sterilization processes (11)
while
remaining resistant to corrosion and providing a longer lifespan than those without
it. (12)
Nickel plays different roles in technologies that have revolutionized the way in which
we communicate. The majority of mobile phones, digital camera and laptop
computers are powered mostly by a Ni-containing rechargeable battery (13)
.
Nickel‟s unparalleled properties have made its presence crucial for sustainable
industrial performance. It helps industry remain productive and profitable, even in
extreme environments. Nickel plays an important role in making the chemical
reactions environmentally friendly. It retains its strength and catalytic properties at
high temperatures, allowing it to withstand the extremely hot conditions (850-1000
°C) involved in petrochemical processes. Ni-catalysts are also used to hydrogenate
vegetable oil in the production of margarine and in the production of fertilizers.
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Nickel plays a role in many of our key modes of transportation. Be it nickel alloys in
the batteries of hybrid cars (14)
or in the turbines of jet engines, or nickel-containing
stainless steel in passenger trains and subways, nickel is a crucial element enabling us
all to get from place to place. The unique properties of Ni-alloys play a key role in
contributing to aircraft fuel efficiency. Historically, airplanes have been made from
aluminium. Today planes are made from composites materials that contain 36% Ni-
alloy called Invar (15)
.
With countless applications, the development of such a unique material is helping
space research go “where no man has gone before”. Nickel is everywhere in today‟s
society, silently serving to make our lives better, and will be contributing to our lives
for many years to come.
I.2.2 COBALT
Symbol : Co
Atomic number : 27
Atomic mass : 58.94
Family : Group 9 (VIIIB), Transition metal
Electronic configuration : 1s2 2s
2 2p
6 3s
2 3p
6 3d
7 4s
2
DISCOVEREY AND NAMING
„Cobalt‟ is a word derived from the German kobold meaning "goblin" or
"mischievous spirit." The term originated in the 16th century when arsenic-containing
cobalt ores were dug up in the silver mines of the Harz Mountains. Believing that
these ores contained copper, miners heated them and were injured by the toxic arsenic
trioxide vapours that were released. These "evils" were then attributed to the goblin or
kobold. George Brandt was the Swedish chemist who first isolated the element in
1742 (16)
, although cobalt had been used for centuries as the blue colour in decorative
glass and pottery.
OCCURRENCE
The stable form of cobalt is created in supernovas via the r-process. It comprises
0.0029% of the Earth's crust and is one of the first transition metal series.
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Cobalt occurs in copper and nickel minerals and in combination with sulfur and
arsenic in the Cobaltite (CoAsS), Safflorite (CoAs2) and Skutterudite (CoAs3)
minerals. The mineral Cattierite is similar to Pyrite and occurs together with Vaesite
in the copper deposits in the Katanga Province.
ISOTOPES AND OXIDATION STATES
59Co is the only stable isotope of cobalt to exist in nature. 22 radioisotopes have been
characterized with the most stable being 60
Co with a half-life of 5.2714 years, 57
Co
with a half-life of 271.79 days, 56
Co with a half-life of 77.27 days, and 58
Co with a
half-life of 70.86 days. All of the remaining radioactive isotopes have half-lives that
are less than 18 hours, and the majority of these are less than 1 second. This element
also has 4 meta states, all of which have half-lives less than 15 minutes.
In its compounds cobalt nearly always exhibits a +2 or +3 oxidation state, although
states of +4, +1, 0, and -1 are known. The compounds in which cobalt exhibits the +2
oxidation state are called cobaltous, while those in which cobalt exhibits the +3
oxidation state are termed cobaltic.
PHYSICAL AND CHEMICAL PROPERTIES
Cobalt is a hard lustrous grey metal. It has high melting point of 1493 °C and a
boiling point of 2927 oC and it retains its strength to a high temperature. The crystal
structure of cobalt is a hexagonal closed packed.
Figure I-IV: CRYSTAL STRUCUTRE OF COBALT
Adapted from An Introduction to Ionic Solids, Retrieved January 12, 2013, from
http://www.everyscience.com/Chemistry/Inorganic/Ionic_Solids/a.1296.php. Copyright 2011 by Every
Sciences. Reprinted with permission.
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It is ferromagnetic metal with a specific gravity of 8.9 (20°C). The Curie temperature
is 1115 °C, and the magnetic moment is 1.6–1.7 Bohr magnetons per atom.
Cobalt is chemically active in that it readily combines with other elements to form
many different compounds. e.g. salts and oxides etc. Cobalt is a weak reducing metal
that is protected from oxidation by a passivating oxide film, as is typical for most
metals. It is attacked by halogens and sulfur. Cobalt forms two well-defined binary
compounds with oxygen: cobaltous oxide (CoO), and tricobalt textroxide (Co3O4).
COMPLEXES OF Co(II)
Both Co2+
and Co3+
form numerous coordination compounds, or complexes.
Co3+
forms more known complex ions than any other metal except platinum.
The coordination number of the complexes is generally six. Cobalt(III) complexes are
almost always low-spin octahedral. Cobalt(II) forms both tetrahedral and octahedral
complexes; square planar complexes are very rare.
BIOLOGICAL ROLE OF Co(II)
Cobalt is an essential element in human and animal metabolisms. Cobalt is the central
atom in each molecule of vitamin B12 which helps the body make blood. Cobalt is
also involved in the biochemistry of methane-producing bacteria that live in
composting soil and in animal intestines. Cobalt soil dressings or implants are used to
supplement cobalt deficient soils to prevent "wasting disease" in grazing animals (17)
.
Although, far less common than other metalloproteins (e.g. those of zinc and iron),
cobaltoproteins are known aside from B12. These proteins include methionine
aminopeptidase 2 and nitrile hydratase.
TOXICOLOGY AND HEALTH
Cobalt is an essential element for life in minute amounts. The LD50 value for soluble
cobalt salts has been estimated to be between 150 and 500 mg/kg. Thus, for a 100 kg
person the LD50 would be about 20 grams.
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After nickel and chromium, cobalt is a major cause of contact dermatitis. In 1966, the
addition of cobalt compounds to stabilize beer foam in Canada led to cardiomyopathy,
which came to be known as beer drinker's cardiomyopathy.
USES OF COBALT
Cobalt is considered as a strategic metal by the United States Government. It is
renowned for its price variation and the colorful character. Cobalt has played a role in
science and culture for thousands of year, tracing as far back as ancient Egypt, where
its distinct blue color sparkled in jewellery and ceramic glazes. Today it is recognized
for its diverse energy, efficiency and environmental benefits.
The main use of cobalt remained as a coloring agent right up to the 20th Century. The
modern uses blossomed with the work of Elwood Haynes on StelliteR alloys, the
development of Alnico magnets in Japan and the use of cobalt to bind tungsten
carbide in Germany. The following discussion will help to manifests that – “The
relationship of this essential metal to our daily lives is simple - modern society
without cobalt cannot function!”
Co-based alloys are also wear-resistant. This makes them useful in the medical field,
where cobalt is often used (with titanium) for orthopedic implants (18)
. Rechargeable
batteries like Ni-Cd, nickel metal hydride or Li-ion systems are ubiquitous in portable
electronic devices, whether in digital cameras, iPods, laptops, mobile phone or power
tools. Whichever type a battery may be, cobalt is an essential constituent (19)
, not least
because it improves the battery's properties.
The magnet industry will always be a considerable user of cobalt. The applications of
permanent magnets such as Alnico magnets, comprises of an endless list. To name a
few - loudspeakers, hearing aids, cathode ray focusing, microphones, musical
instrument microphones, telephone ringers, generators, magnetic separators, etc.
The artificial radioisotope, cobalt-60 is used in radiotherapy, sterilization of medical
supplies and medical waste, radiation treatment of foods for sterilization, industrial
radiography, etc.
Cobalt‟s unique combination of catalytic properties such as its oxidation-reduction
properties, its ability to demonstrate several valencies with easy electron transfer, its
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complexing skills, the vacancies in the crystal lattices of solid cobalt compounds, etc.
are the facts on which the modern industry depends (20, 21)
. Cobalt catalysts are used in
hydrodesulphurization for oil and gas [22]
, for the production of terephthalic acid and
di-methylterephthalate [23]
, etc.
The chart below shows the end uses of cobalt in different areas:
Figure I-V: END USES OF COBALT
Adapted from Cobalt Facts – Formation Metals Inc., Retrieved November 18, 2012, from
http://www.formationmetals.com/i/pdf/factsheet_cobalt.pdf. Copyright 2012 by Idaho Cobalt.
Reprinted with permission.
The ability to cut metal faster and faster is to a great extent at the heart of the
economic growth in the 20th
century. Iron was the first choice but it was cobalt which
became the most successful binding material. Since then cobalt is preferred in the
hard metal/diamond tool industry. There is worldwide interest in nano-grained
WC/Co materials, and many efforts have been made to synthesize nano-grained
WC/Co composites by reduction in grain size (24)
to meet the challenge of obtaining
improved properties.
In March 2011, scientists have passed a chemistry milestone by creating the world‟s
first practical photosynthesis device (25)
. The first artificial leaf was developed more
than a decade ago by John Turner (US National Renewable Energy Laboratory).
Although efficient at carrying out photosynthesis, his device was impractical for
wider use, as it was composed of rare, expensive metals and was highly unstable, with
a lifespan of barely one day. Nocera‟s (Scientist of Massachusetts Institute of
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Technology) new leaf overcame these problems. The key to this breakthrough is
Nocera‟s discovery of several powerful new, inexpensive catalysts, made of nickel
and cobalt that uses sunlight and are capable of efficiently splitting water into its two
components, hydrogen and oxygen, under simple conditions. Right now, Nocera‟s
leaf is about 10 times more efficient at carrying out photosynthesis than a natural leaf.
Scientists are working to increase the device‟s efficiency still higher.
The technology of „Blue Cobalt‟ is promising us „Green Chemistry‟ for the coming
future! It is clearly evident that the production and use of cobalt supports sustainable
development and generates wealth on seven of the world's continents. Truly, Cobalt is
more than just Blue!
I.2.3 ZINC
Symbol : Zn
Atomic number : 30
Atomic mass : 65.38
Family : Group 12 (IIB), Transition metal
Electronic configuration : 1s2 2s
2 2p
6 3s
2 3p
6 3d
10 4s
2
DISCOVEREY AND NAMING
Although zinc compounds have been used for at least 2,500 years in the production of
brass, zinc wasn't recognized as a distinct element until much later. Metallic zinc was
first produced in India sometime in the 1400s by heating the mineral calamine
(ZnCO3) with wool. Zinc was rediscovered by Andreas Sigismund Marggraf (26)
in
1746 by heating calamine with charcoal. Today, most zinc is produced through the
electrolysis of aqueous zinc sulfate (ZnSO4).
OCCURRENCE
Zinc makes up about 75 ppm (0.0075%) of the earth's crust, making it the 24th
most
abundant element there. Soil contains 5–770 ppm of zinc with an average of 64 ppm.
Seawater has only 30 ppb zinc and the atmosphere contains 0.1–4 µg/m3 of zinc.
The element is normally found in association with other base metals such as copper
and lead in ores. Zinc is a chalcophile, meaning the element has a low affinity for
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oxides and prefers to bond with sulfides. Sphalerite which is a form of zinc sulfide, is
the most heavily mined zinc containing ore because it contains 60–62% of zinc. Other
minerals from which zinc is extracted, include Smithsonite (zinc carbonate),
Hemimorphite (zinc silicate), Wurtzite (another zinc sulfide) and sometimes
Hydrozincite (basic zinc carbonate).
ISOTOPES AND OXIDATION STATES
Five isotopes of zinc occur in nature: 64
Zn (most abundant), 70
Zn, 66
Zn, 67
Zn and 68
Zn.
Several dozen radioisotopes have been characterized. This element also has 4 meta
states. Zinc is, in some respects, chemically similar to magnesium, because its ion is
of similar size and its only common oxidation state is +2. However, it also exists in
+1 and 0 oxidation state.
PHYSICAL AND CHEMICAL PROPERTIES
Zinc is a bluish-white, lustrous, diamagnetic metal, though most common commercial
grades of the metal have a dull finish. It is somewhat less dense than iron and has a
hexagonal crystal structure. The metal is hard and brittle at most temperatures but
becomes malleable between 100 °C and 150 °C. Above 210 °C, the metal becomes
brittle again and can be pulverized by beating. Zinc is a fair conductor of electricity. It
has relatively low melting (419.5 °C) and boiling points (907 °C).
Figure I-VI: CRYSTAL STRUCUTRE OF ZINC
Adapted from Zinc crystal structure, molecular model, Retrieved January 12, 2013, from
http://www.sciencephoto.com/media/408885/view. Copyright 2009 by Science Photo Library.
Reprinted with permission.
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Zinc reacts readily with acids, alkalis and other non-metals. The surface of the pure
metal tarnishes quickly, eventually forming a protective passivating layer of the basic
zinc carbonate, Zn5(OH)6(CO3)2, by reaction with atmospheric carbon dioxide. This
layer helps prevent further reaction with air and water. ZnO is a white powder that is
nearly insoluble in neutral aqueous solutions, but is amphoteric, dissolving in both
strong basic and acidic solutions. The other chalcogenides (ZnS, ZnSe, and ZnTe)
have varied applications in electronics and optics.
COMPLEXES OF Zn(II)
The most common structure of zinc complexes is tetrahedral which is clearly
connected with the fact that the octet rule is obeyed in these cases. Nevertheless,
octahedral complexes comparable to those of the transition elements are not rare. A
very large number of metallo-enzymes contain zinc(II). Also, many proteins contain
zinc for structural reasons. The zinc ion is invariably 4-coordinate with at least three
ligands that are amino-acid side-chains.
BIOLOGICAL ROLE OF Zn(II)
All life on earth has evolved in the presence of zinc, which is used by nature for many
biological processes. All living organisms including man, animals, fish, plants and
micro-organisms need zinc for growth and development. Zinc intake is regulated by
each organism‟s natural processes. Two examples of zinc-containing enzymes are
carbonic anhydrase and carboxypeptidase which are vital to the processes of carbon
dioxide regulation and digestion of proteins, respectively.
TOXICOLOGY AND HEALTH
Zinc toxicity can occur in acute as well as chronic exposures. Intakes of 150 to 450
mg of zinc per day have been associated with reduced blood levels of copper and
HDL (high-density lipoproteins) or "good" cholesterol. Abnormally high zinc levels
can also alter iron function and reduce immune function. Breathing zinc dust may
cause dryness in the throat, coughing, general weakness and aching, chills, fever,
nausea and vomiting. Extensive exposure to zinc chloride can cause respiratory
disorders.
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Zinc can be a danger to unborn and newborn children. When their mothers have
absorbed large concentrations of zinc, the children may be exposed to it through blood
or milk of their mothers and get affected. Many cases of zinc poisoning from food
have resulted from the storage of food or drink in galvanized containers.
USES OF ZINC
When asked to describe how zinc is used, most people name vitamins or perhaps sun-
creams. Some may add galvanizing and die casting to the list, but few are aware of the
extent to which zinc and zinc-based technology contributes to our daily lives. Zinc is
integrally involved in transportation, medicine, energy conservation, pollution control,
electronics and space exploration.
Zinc castings are everywhere in today‟s society (27)
from light fixtures to faucets, from
door handles to car parts. Radios, fax machines, computers and printers are but a few
of the modern technologies that rely on diecast zinc parts. Rolled zinc sheets and
strips are used for roofing, cladding, flashings and rainwater disposal applications.
The steel and zinc industries have worked together for many years to perfect
galvanized coatings capable of protecting steel from corrosion (28)
.
Recent advances in medical science are revealing the importance of zinc for the
proper functioning of the immune system, the transfer of nervous signals, the
expression of genes and many other vital functions. Over 4,50,000 children die each
year due to zinc deficiency. In 2008, the Copenhagen Consensus, concluded that
combating the world‟s malnutrition problem through the provision of vitamin A and
zinc was ranked the highest among the various cost-effective solutions to the world‟s
pressing problems.
Martina M. Cartwright in his recent publication in Food For Thought (March 7, 2011)
invoked the supernatural power of zinc (29)
. He claimed that zinc lozenges if taken in
the right dose, at the right time (first 24 hours) and in the right formulation, may
reduce cold symptom duration by a day or two. But exactly how well zinc works is a
matter of future research.
Approximately 60% of the zinc produced worldwide originates from mined ores and
the remaining 40% from recycled or secondary zinc recovered from both new and old
scraps. Zinc can be recycled indefinitely, without loss of its physical or chemical
INTRODUCTION CHAPTER I
School of Science, SVKM’s NMIMS University Page 18
properties, thus constituting a valuable and sustainable resource for future
generations.
Zinc is used to purify water, thus contributing to one of the great environmental
problems. Recyclable zinc-air batteries successfully power electric vehicles, offering
another solution to the problem of urban air quality. Zinc is a major constituent of
brass, a health protective metal due to its bacteriostatic qualities. It is an important
pharmaceutical ingredient, providing daily skin care and protection against the
harmful rays of the sun. Zinc is needed in fertilizers that boost crop yields and so help
feed the world‟s growing population and is perhaps one of the greatest service that
can be rendered by anybody to the country and to mankind (30)
.
The end uses of zinc are summarized as below:
Figure I-VII: END USES OF ZINC
Reprinted from International Zinc Association, Retrieved November 24, 2012, from
http://www.zinc.org/basics/zinc_uses. Copyright 2011 by International Zinc Association. Reprinted
with permission.
Despite its many essential uses, sometimes zinc is used purely for entertainment. To
make a glow-in-the-dark object, we want a phosphor that is energized by normal light
and that has a very long persistence. Zinc sulfide has these properties and is used to
create everything from luminescent watch dials to glow-in-the-dark toys. Zinc‟s
phosphorescent properties have also made it a key ingredient in X-ray and television
screens, fluorescent lights and light emitting diodes. Also, fireworks often make use
of zinc dust to create bright, shimmering sparks. A variety of chemicals can be added
to create the brilliant colors, but it is the zinc that sparkles.
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School of Science, SVKM’s NMIMS University Page 19
Despite a long history, zinc is a uniquely modern metal. With its vast array of
properties, zinc has few peers in terms of usefulness in the ever-expanding fields of
science and technology. Its versatility has made it a basic medium for researchers as
they probe new frontiers in physics, chemistry, biology and electrical engineering.
With many thousands of patents and literally millions of products to its credit, zinc
played a supporting role in many of the major inventions of the 20th
Century. From
transistors to lasers, satellites to circuit boards, photocopiers to fuel cells and space to
undersea, no wonder, zinc is truly among the most versatile and essential materials
known to mankind.
I.3 SCOPE AND OBJECTIVES OF THE THESIS
Taking into account the above context, the main scope of the thesis is as follows:-
The primary intention of this thesis is to contribute new gravimetric methods for
nickel(II), cobalt(II) and zinc(II) which can ease and speed up the work of the
laboratory such that it could be used as a basis for future quantification tests. The
aspect of enhancing the selectivity of the methods will be worked upon by the
application of substoichiometric precipitation technique and exploration of different
masking agents. Furthermore, in order to explore the extent of usefulness of the
developed methods, different complex matrices will be spiked with the analyte of
interest and the recovery of the analyte will be evaluated using the developed
methods. Also, emphasis will be made to extrapolate the application of these methods
in actual samples.
From this main scope, some particular objectives emerge for the proper designing of
each of the three new systems. These objectives are presented as follows:
a) To optimize the conditions of precipitation of analyte of interest by studying
the parameters of pH, time of digestion and amount of reagent added
b) To study the interference of the different salts of anions and various cations
using excess of reagents
c) To evaluate the stoichiometry of metal to reagent by substoichiometric
precipitation technique
d) To study the interference of all the cations again using reagent at
substoichiometric level
INTRODUCTION CHAPTER I
School of Science, SVKM’s NMIMS University Page 20
e) To confirm the stoichiometry of metal to reagent by decomposing the known
amount of complex and analyzing the metal content in the complex using
standard methods available in literature
f) To validate the developed methods by spiking the analyte of interest in
complex matrices, processing it through the developed methods and evaluating
the recovery of the analyte
g) To apply the methods for the determination of these elements in actual
samples like ores, alloys, medicines, talcum powder, etc.
h) To carry out the statistical evaluation of the developed method w.r.t. accuracy
and precision.
I.4 ORGANIZATION OF THESIS
The remainder of this thesis describes the research that has been undertaken to
accomplish the aims stated above (Chapter I).
Chapter II deals with the theoretical aspects of gravimetry. It also sheds light on the
importance of selection of organic ligand in development of gravimetric methods. It
ends with the detailed literature review on 2-mercaptobenzothiazole and explores its
ability as an excellent chelating agent. Chapter III focuses on the general experimental
work carried out and involves preparation of reagents and solutions, standardization
procedures for cations, etc. It also includes the chemicals and apparatus used in this
study.
Chapter IV, V and VI are divided into two sections viz. „a‟ and „b‟. Chapter IVa, Va
and VIa describes respectively the development of new methods for the gravimetric
estimation of Ni(II), Co(II) and Zn(II) employing 2-mercaptobenzothiazole in ethyl
alcohol as a chelating agent. Similarly, Chapter IVb, Vb and VIb demonstrates the
validation of the respective developed methods with spiked samples and their
application in actual samples. Chapter VII elucidates the method developed for the
sequential separation of these three elements when present together.
The references used throughout the thesis have been properly cited at the end of each
of the chapter. The summary and conclusions of the chapters IV, V and VI have been
accommodated at the end of section „b‟ of the respective chapters followed by the
references of the particular chapter.
WORKS CITED CHAPTER I
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I.5 WORKS CITED
1. Bouchentouf, A. Commodities for Dummies. s.l. : Wiley Publishing, Inc, Indiana,
2007.
2. Reutar, M. A., Heiskanen, K., Boin, U., Schaik, A., Verhoef, E., Yang, Y. and
Georgalli, G. The Metrics of Material and Metal Ecology – Harmonizing the
Resource, Technology and Environmental Cycles. Amsterdam, The Netherlands :
Elsevier, 2005.
3. Stewart, D. Nickel. [Online] Chemicool. [Cited: February 8, 2013.]
http://www.chemicool.com/elements/nickel.html.
4. Barnett, S. Nickel in Society. Lasting value, innovative solutions. [Online] Nickel
institute. [Cited: December 12, 2012.] http://www.nickelinstitute.org.
5. Barbara, K. R. and Gordon, R. B. 2008, Journal of the Minerals, Metals and
Materials Society, Vol. 60(7), p. 55.
6. Nielsen, F. H., Myron, D. M., Givand, S. H., Zimmerman, T. J. and Ollerich,
D. A. 1975, Journal of Nutrition, Vol. 105, p. 1620.
7. Francesca, M., Cacciafesta, V., Maffia, E., Scribante, A., Alberti, G., Biesuz, R.
and Klersy, C. 2010, American Journal of Orthodontics and Dentofacial
Orthopedics, Vol. 137(6), p. 809.
8. Harf, C., Meyer, S. and Thomas, C. 1991, Galvano-Organo-Traitements de
Surface, Vol. 614, p. 259.
9. Flint, N. 1998, Contact Dermatitis, Vol. 39, p. 213.
10. Accominotti, M., Bost, M., Haudrechy, P., Mantout, B., Cunat, P. J., Comet,
F., Mouterde, C., Plantard, F., Chambon, P. and Vallon, J. J. 1998, Contact
Dermatitis, Vol. 38, p. 305.
WORKS CITED CHAPTER I
School of Science, SVKM’s NMIMS University Page 22
11. Flenner, S. EHEDG Guideline Document 8, Hygienic Equipment Design Criteria,
2nd Edition. [Online] 2004. [Cited: January 10, 2013.]
http://www.ehedg.org/uploads/DOC_08_E_2004.pdf.
12. Thomas, J. ASTM F138 - 08. [Online] [Cited: November 28, 2012.]
http://www.astm.org/Standards/F138.htm.
13. Strasser, G. 1997, Vakuum in Forschung und Praxis, Vol. 9(1), p. 42.
14. Linden, D. and Reddy, T. B. Handbook of Batteries. 3rd. Ed. New York :
McGraw-Hill, 2002.
15. Lagarec, K., Rancourt, D. G., Bose, S. K., Sanyal, B. and Dunlap, R. A. 2001,
Journal of Magnetism and Magnetic Materials, Vol. 236, p. 107.
16. Johanson, P. Cobalt. New York : The Rosen Publishing Group, 2008.
17. Schwarz, F. J., Kirchgessner, M. and Stangl, G. I. 2000, Journal of Animal
Physiology and Animal Nutrition, Vol. 83(3), p. 121.
18. Michel, R., Nolte, M., M., Reich and Loer, F. 1991, Archives of Orthopaedic
and Trauma Surgery, Vol. 110(2), p. 61.
19. Armstrong, R. D., Briggs, G. W. and Charles, E. A. 1988, Journal of Applied
Electrochemistry, Vol. 18(2), p. 215.
20. Ojima, I., Tsai, C. Y., Tzamarioudaki, M. and Bonafoux, D. 2000, Organic
Reactions, Vol. 56, p. 1.
21. Abdel-Kreem, M., Bassyouni, M., Shereen, M., Abdel-Hamid, S. and Abdel-
Aal, H. 2009, The Open Fuel Cells Journal, Vol. 2, p. 5.
22. Hawkins, M. 2001, Applied Earth Science: Transactions of the Institution of
Mining & Metallurgy, Vol. 110(2), p. 66.
23. Richard, J. S. Ullmann's Encyclopedia of Industrial Chemistry. Weinheim :
Wiley-VCH, 2005.
24. Zhang, Y. and Zhang, J. 1995, Xiyou Jinshu Cailiao Yu Gongcheng, Vol. 24(2),
p. 18.
WORKS CITED CHAPTER I
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25. Nocera, D. 2009, Chemical and Engineering News, Vol. 87(7), p. 58.
26. Gray, L. The Elements Zinc. New York : Marshall Cavendish Corporation, 2006.
27. Putnam, R. and Martin, M. Surprising Zinc. [Online] [Cited: January 4, 2013.]
http://www.zinc.org/case_studies_documents/Surprising-Zinc.pdf.
28. Levinson, L. M. and Philipp, H. R. 1986, American Ceramic Society Bulletin,
Vol. 65, p. 639.
29. Cartwright, M. Food for Thought. [Online] Psychology Today. [Cited: January
17, 2013.] http://www.psychologytoday.com/blog/food-thought/201103/zinc-and-the-
common-cold-just-the-facts.
30. General Facts About Zinc. [Online] Zinc Information centre. [Cited: January 18,
2013.] http://www.zincinfocentre.org/zinc_general_facts.html.