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CHAPTER - I

INTRODUCTION

INTRODUCTION CHAPTER I

School of Science, SVKM’s NMIMS University Page 1

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



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.



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.



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.

http://chemistry.about.com/od/periodictableelements/a/printperiodic.htm.%20Copyright%202012%20by%20About.com

http://chemistry.about.com/od/periodictableelements/a/printperiodic.htm.%20Copyright%202012%20by%20About.com



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

http://en.wikipedia.org/wiki/Sulfur

http://en.wikipedia.org/wiki/Pentlandite


http://en.wikipedia.org/wiki/Millerite

http://en.wikipedia.org/wiki/Arsenic

http://en.wikipedia.org/wiki/Nickeline


http://en.wikipedia.org/wiki/Galena

http://en.wikipedia.org/wiki/Iron_meteorite

http://en.wikipedia.org/wiki/Kamacite

http://en.wikipedia.org/wiki/Taenite

http://en.wikipedia.org/wiki/Ore

http://en.wikipedia.org/wiki/Laterite

http://en.wikipedia.org/wiki/Limonite

http://en.wikipedia.org/wiki/Garnierite

http://en.wikipedia.org/wiki/Pentlandite

http://en.wikipedia.org/wiki/Cubic_crystal_system



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



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.

http://chemistry.about.com/od/periodictableelements/a/printperiodic.htm.%20Copyright%202012%20by





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.



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


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.



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.


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.


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.

http://www.britannica.com/EBchecked/topic/436613/oxidation-number

http://en.wikipedia.org/wiki/Cubic_crystal_system

http://www.everyscience.com/Chemistry/Inorganic/Ionic_Solids/a.1296.php



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.


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.

http://www.britannica.com/EBchecked/topic/65516/binary-compound



http://www.britannica.com/EBchecked/topic/136410/coordination-compound

http://www.britannica.com/EBchecked/topic/129980/complex-ion

http://www.britannica.com/EBchecked/topic/136433/coordination-number



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



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



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


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



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).


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.


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.

http://en.wikipedia.org/wiki/Celsius

http://en.wikipedia.org/wiki/Celsius

http://en.wikipedia.org/wiki/Electrical_conductivity

http://www.sciencephoto.com/media/408885/view



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.


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.



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



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.

http://www.zinc.org/basics/zinc_uses



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



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


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.



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.



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.

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