1. 1
A
PROJECT REPORT
ON
CHROME TANNED
LEATHER
AT
SUPER TANNERY LTD.
JAJMAU, KANPUR
2014
Submitted to
Mr. Imraan Siddiqui
Director
Under The OrganizationalGuidance of Submitted By
Mr. NaseerKhan Anam Khanam
(Training Incharge) (Chem engg)
CSJMA11001390186
UNIVERSITY INSTITUTE OF ENGINEERING & TECHNOLOGY,
CSJMU KANPUR

2. 2
Acknowledgement
A summer project is a golden opportunity for learning and self development. I consider
myself very lucky and honored to have so many wonderful people lead me through in
completion of this project.
I express my deepest thanks to “Mr. Imraan Siddiqui, Super Tannery, Kanpur, for taking
part in useful decision & giving necessary advices and guidance and arranged all facilities
to make life easier. I choose this moment to acknowledge their contribution gratefully.
I wish to express my indebted gratitude and special thanks to “Mr. Naseer Khan “ ,
Training In charge, Super Tannery, Kanpur" who in spite of being extraordinarily busy
with her/his duties, took time out to hear, guide and keep me on the correct path and
allowing me to carry out my industrial project work at their esteemed organization and
extending during the training.
A humble ‘Thank you’ Sir.
It is my glowing feeling to place on record my best regards, deepest sense of gratitude for
the faculty of UIET, Chhatrapati Shahu Ji Maharaj University Kanpur for their guidance
and support, their judicious and precious guidance which were extremely valuable for my
study both theoretically and practically.
Last but not the least I express my deepest thanks to my parents. They supported me by
showing different method of information collection about the company. They helped all
time when i needed and they gave right direction toward completion of project.
Anam Khanam
25.06.2014

3. 3
About The Company
Super Tannery Ltd (STL), established in 1953, started operations by processing 50 Buffalo hides per
day, converting them into Vegetable Tanned Leather for shoe soles. Since then, the company, well
guided by a professional approach, has marked an important name for itself in the world leather map,
making it, one of the oldest and well reputed business houses of Northern India.
Strong belief in value addition led the company to innovate new products by adding value to the existing
ones. From the time of producing
leather for shoe soles, the
company's product range now
includes:
Leather for:
 Safety and Casual Footwear
 Upholstery
 Lining
 Shoe soles
 Equestrian equipment
Footwear:
 Military
 Safety
 Casual and Formal
 Kids
Accessories:
 Bags
 Belts
 Jackets
 Jewellery
STL owns and operates 5 independent manufacturing facilities, producing articles of the highest quality
for leading European and American brands. Employing more than 2000 people, with annual sales of over
USD 55 Million, the company has its customers in more than 40 countries. It has offices and warehouses
in the United Kingdom, United Arab Emirates, Malaysia and China.
STL's obsession with quality and social responsibility has led the company to achieve ISO 9001:2000,
ISO 14001:2004 and

4. 4
SA 8000:2001 certifications. Stringent norms for procurement, processing, production and dispatch have
transformed STL as one of the most reputed manufacturing entities.
STL is committed to continuous technological innovation, physical and chemical standardization and
improvement to achieve high standards of product quality
and customer satisfaction
Key factors that keep the company one step ahead:
1. Extensive interaction with the latest technological
developments.
2. Presence in all major trade fairs, seminars and workshops for
optimum knowledge upgradation.
3. Well qualified and progressive workforce.
Laboratory: The tannery units of the company work under guidance of a well equipped laboratory
conducting physical and chemical tests. It also has a pilot tannery to conduct trials of new leathers at a
small scale before its implementation in bulk production. The laboratory has all the requisites to perform
tests of leather as per EN, ISO and DIN standards. STL was among the first companies from Kanpur to
provide certification as per the REACH guidelines of European Chemicals Agency.
DesignStudio: The footwear units of the company conduct their production as per the guidance of a
newly built, state of the art designing cell, lead by well qualified shoe technologists and designers. Due to
a rapid change in the product profile over the past few years, this studio was installed keeping in mind,
the ever changing tastes and preferences of the customers, while keeping time frame into consideration.
Quality Assurance: A major factor which keeps the company ahead is its obsession with total quality,
which includes products of the highest standards, quick and efficient customer service, leading to
complete customer satisfaction. Factors like these help the company to retain customers, some of them,
for as long as 30 years.
When the leather industry enough developed, the pollution of air and water
increased and the stage reached where scientists started thinking on making
better use or reuse of material which caused pollution keeping in mind the
economical factor else no industrialist would accept the change.
Special emphasis has been laid on use of low waste technology with

5. 5
minimum possible expenditure and maximum quality production because it is natural for any
industrialists to resist a change unless it is likely to give better quality production with least expenditure.
Pollution is given the last priority by them whereas we give it the first priority.
At Super Tannery, we are very much cautious about pollution. We have our own water treatment and
chrome recovery plant in which we collect the drain water full of nickel, chromium and many more
harmful substances. Our deep interest is in green and clean environment.
The chrome is used in the processing of skins in which 65% is consumed during the process while
35% goes waste. The presence of chrome in the discharged water of tanneries is hazardous for public
health as its excessive use can cause severe skin diseases. To minimize the danger we have water
treatment plant to purify water to its maximum possible level.
We believe to contribute in safe and healthy environment. Super Tannery is an eco friendly tannery.
 We at Super are committed to provide a safe and healthy working environment for our employees by
adopting a proactive approach.
 It is part of our work ethic to ensure that safety, health and environment safeguards are in place right
from the inception to the execution stage.
 We accept the need for constant upgradation of safety & health standards commensurate with the rapid
changing technology in production.

6. 6
INTRODUCTION
In ancient history, tanning was considered a noxious or "odiferous trade" and relegated to the
outskirts of town, amongst the poor. Indeed, tanning by ancient methods so foul smells that
tanneries are still isolated from those towns today where the old methods are used. The ancients
used leather for water skins, bags, harnesses, boats, armor, quivers, scabbards, boots and sandals.
Around 2500 BC, the Sumerians began using leather, affixed by copper studs, on chariot wheels.
Skins typically arrived at the tannery dried stiff and dirty with soil and gore. First, the ancient
tanners would soak the skins in water to clean and softenthem. Then they would pound and
scour the skin to remove any remaining flesh and fat. Next, the tanner needed to remove the hair
fibers from the skin. This was done by soaking the skin in urine, painting it with an alkaline lime
mixture, or simply letting the skin putrefy for several months then dipping it in a salt solution.
After the hair fibers were loosened, the tanners scraped them off with a knife.
Once the hair was removed, the tanners would bate the material (see below) by pounding dung
into the skin or soaking the skin in a solution of animal brains. Among the kinds of dung
commonly used was that of dogs or pigeons. Sometimes the dung was mixed with water in a
large vat, and the prepared skins were kneaded in the dung water until they became supple, but
not too soft. The ancient tanner might use his bare feet to knead the skins in the dung water, and
the kneading could last two or three hours.
It was this combination of urine, animal feces and decaying flesh that made ancient tanneries so
odiferous.
Children employed as dung gatherers were a common sight in ancient cities. Also common were
"piss-pots" located on street corners, where human urine could be collectedfor use in tanneries or
by washerwomen. In some variations of the process, cedar oil, alum or tannin were applied to the
skin as a tanning agent. As the skin was stretched, it would lose moisture and absorb the agent.
Leftover leather would be turned into glue. Tanners would place scraps of hides in a vat of water
and let them deteriorate for months. The mixture would then be placed over a fire to boil off the
water to produce hide glue.
Variations of these methods are still used by do-it-yourself outdoorsmen to tan hides. The use of
brains and the idea that each animal (except buffalo) has just enough brains for the tanning
process have led to the saying "Every animal has just enough brains to preserve its own hide,
dead or alive."

7. 7
In Tannery, Raw materials are Skin And Hides..
Skin: - Outer covering of small animals like goat.
Hide: - Outer covering of big animals like cow, buffaloes, ox camels etc.
Hides = 2* sides
Slaughtering
Flaying
(Removal of skin)
Curing
(To protect before sell)
Market
Tannery

8. 8
Slaughtering & Flaying
The actual tanning process begins with the obtaining of an animal skin. When an animal skin
is to be tanned, the beast is killed and skinned before the body heat leaves the tissues. This
can be done by the tanner, or by obtaining a skin at a slaughterhouse or farm.
Curing
Preparing hides begins by curing them with salt. Curing is employed to prevent putrefaction
of the protein substance (collagen) from bacterial growth during the time lag that might occur
from procuring the hide to when it is processed. Curing removes excess water from the hides
and skins using a difference in osmotic pressure. The moisture content of hides and skins gets
greatly reduced. In wet-salting, the hides are heavily salted, then pressed into packs for about
30 days. In brine-curing the hides are agitated in a salt water bath for about 16 hours.
Generally speaking, curing substantially reduces the chance of spoilage by bacteria. Curing
can also be done by preserving the hides and skins at a very low temperature.
IN TANNERIES FOLLOWING PROCESSES ARE FOLLOWED FOR THE
MANUFACTURING OF FINISHED CHROME LEATHER:-
Tannery
Pre-
Tanning
Tanning
Post
Tanning
Finishing

9. 9

10. 10
Beamhouse operations
The steps in the production of leather between curing and tanning are collectively referred to
as beamhouse operations. They include, in order, soaking, liming, removal of extraneous
tissues (unhairing, scudding, and fleshing), deliming, bating (including puring), drenching,
and pickling.
1. Soaking
This process is done in pit/paddles. In the process known as soaking, the hides are soaked in
clean water to remove the salt left over from curing and increase the moisture so that the hide
or skin can be further treated.
 Enzymes are also added for the strengthening of fibers of skin/hide.
 0.025% Antibacterial agent (Preservative) is added.
2. Liming
This process is also done in pit/paddles. After soaking, the hides and skins are taken
for liming:treatment with milk of lime (a basic agent) that may involve the addition of
"sharpening agents" (disulfide reducing agents) like sodium sulfide, cyanides, amines etc.
The objectives of this operation are mainly to:
 Remove the hairs, nails and other keratinous matter
 Remove some of the interfibrillary soluble proteins like mucins
 Swell up and split up the fibers to the desired extent
 Remove the natural grease and fats to some extent
 Bring the collagen in the hide to a proper condition for satisfactory tannage
The chemical reaction involve here is
CaO + H2O + Na2S → Ca(OH)2 + NaOH + NaHS
The weakening of hair is dependent on the breakdown of the disulfide link of the amino acid
called cystine, which is the characteristic of the keratin class of protein that gives strength to
hair and wools (keratin typically makes up 90% of the dry weight of hair).
The hydrogen atoms supplied by the sharpening agent weaken the cystine molecular link
whereby the covalent disulfide bond links are ultimately ruptured, weakening the keratin. To
some extent, sharpening also contributes to unhairing, as it tends to break down the hair
proteins.
Ca(OH)2 : swells the hide
NAHS: hair removal

11. 11
The isoelectric point of the collagen in the hide (this is a tissue strengthening protein
unrelated to keratin) is also shifted to around 4.7 due to liming.
Mechanical Operations
Unhairing and scudding
Unhairing agents used at this time are: Sodium sulfide, sodium hydroxide, sodium
hydrosulfite, calcium hydrosulfide, dimethyl amine, and Sodium sulfhydrate. The majority of
hair is then removed mechanically, initially with a machine and then by hand using a dull
knife, a process known as scudding.
Fleshing
This is a continuation of the scraping or fleshing that was done by hand. In the tannery it is
completed on a shaving machine. It has the effect of stretching the skin as well as cleaning
the flesh side.
3. Deliming and bating
The pH of the collagen is brought down to a lower level so that enzymes may act on it, in a
process is known as deliming. Deliming agents used are commonly
 (NH)4SO4
 NH4Cl
Mostly (NH)4SO4 is used in industry as it has less ammoniacal nitrogen content.
Depending on the end use of the leather, hides may be treated with enzymes to soften them, a
process called bating.
 To check deliming is completed, we cut out a small cross-section & dropped some
phenolphthalein indicator.
 If pink color appears , means deliming is not completed
 Again run the drum for an hour & continue it until Colorless cross-section comes out
after indicator.
 pH should be 7.0 - 8.0
4. Pickling
Once bating is complete, the hides and skins are treated with a mixture of common
(table) salt and sulfuric acid, in case a mineral tanning is to be done. This is done to bring
down the pH of collagen to a very low level so as to facilitate the penetration of mineral

12. 12
tanning agent into the substance. This process is known as pickling. The common salt
(sodium chloride) penetrates the hide twice as fast as the acid and checks the ill effect of
sudden drop of pH.
Reaction involved here is
NaCl + H2O → NaOH + HCl
 To check the solubility of salt solution ‘Be 7.0 (Beumometer)
 Then acid should be added after dilution in 1:10.
 Now check the condition by bromophenolBlue indicator (2.8 – 4.6)
 By dropping it on cross-sectionIf yellow to violet color appear means pickling
completed.
 Or check it By Thumb process.It should be elastic.
 Now pH should be 2.8 – 3.2
TANNING OPERATIONS
Vegetable tanning
Vegetable tanning uses tannin. The tannins (a class of polyphenol astringent chemical) occur
naturally in the bark and leaves of many plants. Tannins bind to the collagen proteins in the
hide and coat them causing them to become less water-soluble, and more resistant to bacterial
attack. The process also causes the hide to become more flexible. The primary barks,
processed in Bark mills and used in modern times
are chestnut, oak, redoul,tanoak, hemlock, quebracho, mangrove, wattle (acacia; see catechu),
and myrobalan. Hides are stretched on frames and immersed for several weeks in vats of
increasing concentrations of tannin. Vegetable tanned hide is flexible and is used for luggage
and furniture.
Chrome tanning
Prior to the introduction of the basic chromium species in tanning, several steps are required
to produce a tannable hide. These steps include: Scudding (removing the hair), Liming (the
introduction of alkali agents such as sodium hydroxide), Deliming (restoring neutral pH),
Bating (softening the skin with enzymes), and Pickling (lowering pH of the hide with salt and
sulfuric acid). The pH is very acidic when the chromium is introduced to ensure that the
chromium complexes are small enough to fit in between the fibers and residues of the

13. 13
collagen. Once the desired level of penetration of chrome into the substance is achieved, the
pH of the material is raised again to facilitate the process. This step is known as
"basification". In the raw state chrome tanned skins are blue and therefore referred to as "wet
blue." Chrome tanning is faster than vegetable tanning (less than a day for this part of the
process) and produces a stretchable leather which is excellent for use in handbags and
garments.
Tanning withother minerals
As chrome tanned hides and skins are called 'wet blue', other forms of tanning like the ones
based on alum, zirconium, titanium, iron salts or a combination thereof lead to 'wet white'.
Wet white is also a semi finished stage like wet blue, but is much more eco friendly. The
shrinkage temperature of wet white varies from 70 to 85 degree Celsius,
Here we are goingto studyabout ChromeTanning
Chrome tanning
Today, 80-90%of leathers in the world are tanned by chrome tanning. Chrometanninguses
a solution of chemicals, acids and salts (including chromium sulphate) to tan the hide. It’s a
very quick process, taking abouta day to produce a piece of tanned leather. First hideare
limed to remove hair and then are “pickled” by being left in the acid salt mixture, before
being placed in the chromium sulphate. All hides then come out looking light blue (known as
“wet blue”).
In 2008, about24 million tones of chromium wasproduced. About 2% of it has been used
for the production of chromium sales, such as chromium sulphate, for the making of leather
tanning materialsbutalso for the production of dyestuffs and plastics. Worldwide
approximately 480,000tons of chromium tanninsare produced per year.
The most importantchrome deposits are found in South Africa accounting for 33% of
production, while India and Kazakhstanprovided 20% and 17% respectively. Brazil,
Finland, Oman, Russia, and Turkeytogether contributed a further 21%, while some 12
smaller producer countries broughtthe balanceof 9%.

14. 14
Main advantagesof chrome tanning
• Quick and easy to produce, usuallyonly taking up to a day
• Water can roll off the surface easily with appropriateretanning and
finishing processes
• Soft and suppleto the touch
• It is possible to obtain leather with a stable colour
• It is cheaper to buy than vegetable tanned leather, which meansit is also
easier to find
• It has a high degree of thermal resistance
Chemistry of chrome tanning
Chromium(III) sulfate ([Cr(H2O)6]2(SO4)3 has long been regarded as the most efficient and
effective tanning agent Chromium(III) compounds of the sort used in tanning are significantly
less toxic than hexavalent chromium. Chromium(III) sulfate dissolves to give the
hexaaquachromium(III) cation, [Cr(H2O)6]3+, which at higher pH undergoes processes
called olation to give polychromium(III) compounds that are active in tanning being the
cross-linking of the collagen subunits. The chemistry of [Cr(H2O)6]3+ is more complex in the
tanning bath rather than in water due to the presence of a variety of ligands. Some ligands
include the sulfate anion, the collagen's carboxyl groups, amine groups from the side chains
of the amino acids, as well as "masking agents." Masking agents are carboxylic acids, such
as acetic acid, used to suppress formation of polychromium (III) chains. Masking agents
allow the tanner to further increase the pH to increase collagen's reactivity without inhibiting
the penetration of the chromium (III) complexes.
Collagen is characterized by a high content of glycine, proline, and hydroxyproline, usually in
the repeat -gly-pro-hypro-gly-These residues give rise to collagen's helical structure.
Collagen's high content of hydroxyproline allows for significant cross-linking by hydrogen
bonding within the helical structure. Ionized carboxyl groups (RCO2
-) are formed by
hydrolysis of the collagen by the action of hydroxide. This conversion occurs during the
liming process, before introduction of the tanning agent (chromium salts). The ionized
carboxyl groups coordinate as ligands to the chromium (III) centers of the oxo-hydroxide
clusters

15. 15
Tanning increases the spacing between protein chains in collagen from 10 to 17 Å the
difference is consistent with cross-linking by polychromium species, of the sort arising from
olation and oxolation.
Subsequent to application of the chromium agent, the bath is treated with sodium bicarbonate
to increase the pH to 4.0–4.3. This increase induces cross-linking between the chromium and
the collagen. The pH increase is normally accompanied by a gradual temperature increase up
to 40 °C Chromium's ability to form such stable bridged bonds explains why it is considered
one of the most efficient tanning compounds. Chromium-tanned leather can contain between
4 and 5% of chromium. This efficiency is characterized by its increased hydrothermal
stability of the skin, and its resistance to shrinkage in heated water.

16. 16
Masking Agents
Chloride has little tendency to enter the chromium complex but other material may be
strongly attracted into this complex. The reactivity of a number of different organic
materials with chromium in solution can be used to control the chrome tanning process.
Such materials are called Masking Agents because they modify (mask) the chromium
tanning reaction to give improved tanning characteristics.
There are three stages of initialreaction represented as;-
 Solution: The basis chromium sulphate dissolves and as the sulphate ionizes
cationic chromium complex is formed.
 Masking with sodium formate: The formate ion in the solution forms a
basic chromium formate complex with the displacement of some of the
sulphate from the chromium complex. Penetration power of sodium formate
is more so as it absorb BCS & easily penetrate into the hide as the molecular
size of Sodium formate is greater than BCS.
 Basification: it is done by Sodium bicarbonate. As it fix the penetrated
material into the pelt.
 NaHCO3 is added 2.25% diluted in 1:10 with water
 4 feeds with 30 min interval
 Then run for 4 hours
After Basification Material called WET BLUE. The basification
should be verified through-
 BOIL TEST is done then to check the shrinkage. Wet Blue shouldn’t
shrink ≥ 5%
 By Bromophenol Green Indicator- green to blue color should appear.
 Piling & Ageing:-After basification the wet blue hides are pilled in group on
one another called PILING. Then leave for some 48 hours as the basicities of the
chrome components present inside the leathers are increased & therefore chrome

17. 17
fixation & also the tendency of chrome compounds to form new cross linkages are
increased.
 pH then should be 3.8-4.2
 Weighing:- then wet blue is got measured.
MechanicalOperations
Selection: The segregation of tanned leather is done. In this yard for different types of
finished leather/ end use. The selection varies from region to region and as per season.
Splitting: The leather is split into one or more horizontal layers. This can be done after
liming or after chrome tanning. The choice depends on the product we want to achieve.
 Upper Part is called GRAIN.
 Lower part is called FLESH.
Shaving: This operation smoothens the thickness of the whole surface of the skin and
eliminates the residues of fleshing. This operation is carried out with a cylinder machine
where the top one is provided with helical blades.
Trimming: Useless Edges are removed manually by sharp knives to give the wet blue a
proper shape. Thickness of each hide is also checked in this section.
Weighing: Finally Hides are weighed again before any other operation is done. A proper
record is to be maintained. It is then passed on to dye house for further processing.
PostTanning Operations
 Wet Back
 Re-Chroming
 Neutralization & Washing
 Re-Tanning & Dyeing
 Fat Liquoring
 Fixing
Wet Back: Depending upon the condition of wet blue, if it is too dry then wet back is done by
adding 0.25%-0.30% sodium formate with 100% water & run drum for 30-45 mins & drain
water.

18. 18
Re-chroming: This process varies for individual tanners. The shaved hide at this stage has got
open fibers& its weight is reduced by 64% hence the consumption of BCS is reduced. This
process is done in drums. In case of vegetable tanned semi-finished leather, chrome tanning
is given depending on the final leather quality.
 Here 4% BCS with 1.5% NaCOOH is added in first feed & run for 45-60mins.
 Then second feed is added as 2% BCS with 2% sulphonated fish oil
 H2SO2 is added as emulsifying agent on fish oil for emulsion with water.
Neutralization & washing : Chrome tanned leather is acidic in nature after leaving tan
liquor.Mild alkalis are added to the leather,to make it electrically neutral. Due to electrical
neutrality the oil droplets in the fat liquoring stage can’t breakdown. After this leather is
washed completely by plain running water by which the deposits on the surface are washed
away. The float is not drained out after this process but is used for retanning. it for later
chemical processes.
Re-tanning: Retanning is carried out with a combination of vegetable and synthetic tanning
materials. By this process the uneven surface becomes even. The chemicals used are different
tanning agents & Syntans. They provide improved fullness, tighter grain, good buffing
properties. skins as it impairs the tensile strength and makes them more difficult to dye . At
the end of retannage the leather is light in colour. It is a relatively short process involving
about one and a half hours in the drum.
Dyeing: the leather is dyed in drums to give it colour! It can be fixed up to the fabric & when
fixed,is not fugitive that is fast t light & not washable by water, dilute acid or alkali.
Commonly types of dyes are
 Acid Dyes
 Basic Dyes
 Direct dyes
Anionic/Acidic dyes are very common as they are negatively charged and so latch onto the
chrome leathers well. Modes of dyeing are.
 Trough Dyed Leathers(T/D): 2.0/2.5% dye
 Surface Dyed Leather(S/D): 0.25/0.5% dye
 Then dye leveling agents (dispersing agents) are added as 0.10/0.15%

19. 19
Fat liquoring: This process uses fats and oils to lubricate and soften the fibre structure of
leather. The manner in which the oils are introduced into the hide coat every fibre. This is
where leather gets its smell!
This process is done in same drums in which dyeing was done without draining of the float. If
the leather is not fat liquored it becomes dry and hard and breaks when bent. The tensile
strength, stitching tear resistance, abrasion resistance etc improve considerably b fat
liquoring. In addition to the above improvement in physical properties like toughness, water
repellence, resistance to chemical action also. Some stronger hydrophilic groups are
introduced into the oil molecules to increase the affinity of the latter for protein.In tanneries
this is generally done by one of the following methods :-
 Oxidation of oils
 Sulphitation
 Sulphonation
 Saponifacation
 Chlorination
According to the required softness of leather fat liquors are added mostly 5.0- 25% sulphited
or sulphonated fat liquors are used..
Types of fat liquors commonly used are:-
 Synthetic Fat Liquors
 Vegetable Fat Liquors
 Animal Fat Liquors
 Marine(fish) Oil
Free Oils (Neat) is also added as0.25% with 0.02% anti fungal preservatives.
Fixing:- Then the chemicals are fixed up by formic acid. This helps in fixing all the droplets
on fibers.
Piling: -The leather is piled up for 24 hours after completion of fat liquoring. By this process
oil is equally distributed on the surface of leather.

20. 20
Mechanical Operations
Sammying:-It is a mechanized process to remove excess moisture in the wet blue. Only 50-
55% of moisture is left in the leather and remaining water is drained out. Hence the leather is
conditioned for next operation.
Setting:-To remove the wrinkles & folds & grain side smoothen. This also smoothens out
coarse& drawn grain.
Vacuum Drying:- The most significantly in the drying technique applied to leather is the
development of the vacuum dryer. In vacuum drying the leather is spread out grain down on
a smooth or sand blasted, usually chrome plated polished steel surface. Heat is applied to
this surface by a built in heat exchanger. This temperature is maintained by thermostatic
control of circulating hot water & a hood is placed over the plate & then evacuated to aid in
drying the leather.
In vacuum drying the same general rules apply to the heat balance. Since the heat is being
supplied directly from the plate to the leather, rather than being taken from hot air, the entire
drying system changes completely. Evaporation will take place in the fiber inside the leather
& the problem arising from the migration of the tanning materials & oils are greatly
decreased.
Hang Drying & Toggling:- In hang drying the leather in hanged under gravity for drying
as air circulation method. It takes long time to dry & an old method. Toggling has the
advantage of drying large quantities of leather in a relatively small space. In addition it
provides for stretching the leather during drying.
A Toggling unit consists of a number of screens placed in a dryer having controlled
temperature & humidity. The leather is stretched & held in place by a number of clamps that
hook into the screens. Radio frequency is used in drying & for the initiation of chemical
reactions in other industries. Radio frequency can be used to bring leather from a wet
condition to less than 20% moisture in a few seconds without damage.
Stacking:- The modern technique used by increasing number of units is vibration stacking
machine. The latest version of this machine which is modified one is equipped with stacking
& stretching facilities in one operation which softens the leather. This action simultaneously
opens & spreads the leather, thereby enlarging its surface.

21. 21
Trimming: Useless Edges are removed manually by sharp knives to give the wet blue a
proper shape. Thickness of each hide is also checked in this section.
Finishing
The purpose of finishing is to improve the use properties of the leather in general and to protect it
from wetting and soiling, to level out patches and grain faults and to apply an artificial grain
layer to split or correctedgrain leather. Furthermore to modify the surface properties (shade,
lustre, handle, etc.).
The finish of leather can greatly vary mainly depending on the purpose of the leather. Hide
stocks differ in extent of grain damages greatly in the countries. Hides with greater damages have
to be correctedby buffing, which removes more or less much from the natural grain structure.
They are referred to correctedgrain. Therewith the most important element of a natural look gets
lost.
Furthermore leather varies uneven in grain in respect of structure and coloration requires more
pigments and more pigments generate thicker films and the resulting leather becomes more
plastic like. A so-called natural feel or look is made by embossing an artificial grain and by
milling and also by application of a bicolour effect.
 Finishing Materials
Finishing materials may be classifiedinto two main groups:
 Binders which may be waxes, proteins or synthetic polymers
 Additives such as pigments to give color, or surface modifiers
Mechanical finishing operations may include:
Polishing: to create a shiny surface by rubbing it with a velvety wheel
Ironing & Plating: to obtain a flat and smooth surface
Embossing: -to obtain a three-dimensional print
Tumbling: - by rotating the drum quickly to create a more evident grain and a smooth
surface
Chemical Finishing: - involves the application of a film, natural or synthetic by using curtain
coaters, roller coatings and spraying.

22. 22
PHYSICAL PROPERTIES OF FINISHED LEATHER
(BUFFALO GRAIN BARTON)
Sr. No Characteristic ofleather/
parameter of testing
Requirements Units Testmethod
ISI/DIN-EN ISO
1 Tensile Strength 15.0 Min N/mm2 IUP-6DIN53328
2 Elongation At Break 80 Max % IUP-6DIN53328
3 Tear Strength 120 Min N/mm IUP-8DIN53329
4 Flexing Endurance 125000 Min Flexures IUP-20DIN53351
5 Adhesion Of Finished Film 3.0 Min (Dry)
2.5 Min (Wet)
N/cm IUF-407/DIN-
EN/ISO11644
6 Water Penetration 60 Min Minutes IUP-10/DIN53338
7 Water Absorption 30 Max
(After 2 Hrs)
% IUP-7DIN53330
8 Water Vapour Permeability 1.0 Min Mg.cm2/hr IUP-15/DIN53333
9 Water Vapour Co-Efficient 80 Min Cm Hg
Pressure
IUP-15/DIN53333
10 Heat Resistance 180 Max Temp C IUP-13
11 Color Fastness Grade-3
Rubs Min 50
Dry
Rubs IUF-2
12 Grain Distention Of
Crackness
7.0 Min Mm IUP-12/DIN53324

23. 23
CHEMICAL PROPERTIES OF FINISHED LEATHER
(BUFFALO GRAIN BARTON)
Sr.
No.
Characteristic of leather/
parameter of testing
Requirements Test method
ISI/DIN-EN ISO
1 Determination of moisture 10-16 IUP-2
2 Determination of Total Ash 2.0 max IUP-7/DIN-EN/ISO4047
3 Determination Of Sulphated
Ash Water Soluble
0.5 max IUP-7/DIN-EN/ISO4047
4 Determination Of Solvent
Extractable Substances
3-12 IUP-8/DIN-EN/ISO4048
5 Determination Of Nitrogen &
Hide Substances
1.4 max IUP-10/DIN53308
6 Determination Of Water
Soluble Matters
2.0 max IUP-6/DIN53307
7 Determination Of Chromium
Oxide
2.5 max IUP-8/DIN53309
8 Determination Of pH 3.5 max IUP-11/DIN-EN/ISO4045
NOTE: - Except pH all requirements are in %.

24. 24
Objective:-To determine the amount Chromium oxide (Cr2O3)
Requirements: - Small pieces of leather
Glassware’s:- iodine flask 250 ml with stopper, burette (0-50 ml), Hot Plate, Reagent
Bottle
Lab Reagents:-
 Fusion Mixture of acids HClO4,HNO3,H2SO4 in 12:5:3
 Potassium Iodide 10 ml of 10%
 Titration against N/10 Sodium ThioSulphate
 Starch Powder
Preparationof Starch Indicator
1. Take 100 ml distilled water & boil.
2. Add 10g starch powder& shake till powder is in saturated form.
Preparationof N/10 Sodium ThioSulphate
1. Add 24.8 g Na2S2O3.5H2O in 1000 ml of water.
Procedure:-
 Take 1 gm small pieces of leather & put in iodine flask.
 Add 20 ml fusion mixture.
 Put it on hot plate until wine colour appeared.
 Then take it away from hot plate & rest for cool.
 After cooling add 100 ml of distilled water.
 Then coolagain then add 10 ml of 10 % of iodine solution & keep it in dark place
for 10 min ( for the liberation of iodine)
 Take away from dark place titrate the prepared solution against N/10 Na2S2O3.5H2O
solution using starch indicator.
 Stop the titration at end point sky blue colour & note the reading.
Calculations:-

25. 25
Consumption of hypo = 14 ml
1 ml hypo= 2.534 gm of Cr2O3
Cr2O3 content % by weight = (2.534* 14 ml * normality of hypo)/ sample taken
= 3.1675 %
Result: - Testpassed as min requirement was 3.0%

26. 26
WASTE GENERATION IN TANNERIES
Tanning industry is one of the oldest industries in the world. It is typically characterized
as pollutants generated industries which producewide varieties of high strength toxic
chemicals. It is recognized as a serious environmental threat due to high chemical levels
including salinity, organic load (chemical oxygen load or demand, biological oxygen
demand), inorganic matter, dissolved, suspended solids, ammonia, total kjeldahl nitrogen
(TKN), specific pollutants (sulfide, chromium, chloride, sodium and other salt residues)
and heavy metals etc. Large quantity of water is used in tanning process ofwhich 90% of
the water is discharged as effluent. A part of the leather processing, solid and gaseous
wastes are also discharged into the environment. During the chrome tanning process,40%
unused chromium salts are usually discharged in the final effluents, causing a serious
threat to the environment. Exposure to chromium, pentachlorophenol and other toxic
pollutants increase the risk of dermatitis, ulcer nasal septum perforation and lung cancer .
Without any exceptions there is no effluents treatment plant (ETP) in leather tanning
industries in the country and moreover, the owners of tannery industries are not much
concerned about human health and environmental safety.
.Waterusage and waste waterdischarge
Raw to Wet Blue= 25-30 l/kg of hide.
Raw to finish= 30-40 l/kg of hide
A number of research works on tannery effluent treatment using different technologies,
such as flotation, electrochemical treatment, sedimentation, coagulation, filtration, and
ultra-filtration and reverse osmosis process have been reported. Several investigators have
used solid supports, including sand, clay, GAC, glass beds, rocketc. for treating the
effluents. Coagulation or chemical precipitation has been known for wastewater treatment
since the previous century in England where lime was used as coagulant alone and/or in
combination with calcium chloride or magnesium.

27. 27
Characteristics of Wastewater
Sr.
no.
Tanning
Process
Modes of
operation
Water
Usage(liters)
Chemicals used General
Constituents of
waste water
1 Soaking Pits/ paddles 9-12 Wetting,
emulsifying and
bacteria agents
Olive green
obnoxious odor,
contains small
protein suspended
matters & high
amount of Cl
2 Liming Pits/ paddles 2.5-4.0 Lime & Na2S Highly alkaline,
contains high
amount of
sulphides,
Ammonical N2,
suspended solids,
hair pulp and
dissolved solids
3 Deliming Pits/ paddles/ drums 2.5-4.0 Ammonium
salts, enzymatic
bates
alkaline, contains
high amount of
organic matters &
Ammonical N2
4 Pickling &
Chrome
tanning
Drums 2.0-3.0 Common salt,
acids/basic
chrome salts
Colored ,acidic,
contains high
amount of trivalent
chromium, TDS
and Cl, acidic dyes
& oil emulsion
5 Dyeing &
fat
liquoring
Drums 1.0-1.5 Dyes & fatty
acids

28. 28
Tannery wastewater is one of the most pollution sources. It can cause environmental
problems related to its high organic matter, suspended solids and chromium. Chromium
(III) salts are the most widely used chemicals for tanning processes, causing the tannery
wastewater to be highly pollutant with chromium. The main objective of this study is to
investigate the pre-treatment of an actual tannery wastewater using two systems; the first
electrolytic system and the second physico-chemical system. The performances of
electrolytic system at current of 10, 20, 30 and 40 A were discussed. Poorremoval
efficiencies of chemical oxygen demand (COD), total suspended solids (TSS), chromium
(III), ammonia (NH(4) (+) and sulfide (S(2-)) were obtained. In the second physico-
chemical system, calcium hydroxide was used as a coagulant material for chromium
precipitation and plain sedimentation was applied for reducing of COD, biochemical
oxygen demand (BOD(5)) and TSS. The results demonstrate 98.8% removal of
chromium, 31% removal of COD, 25.8% removal of BOD (5) and 51.2% removal of TSS.
PRIMARY WASTERWATER TREATMENT
At Super Tannery,we are very much cautious about pollution. We have our
own water treatment and chrome recovery plant in which we collectthe drain
water full of nickel, chromium and many more harmful substances.Our deep
interest is in green and clean environment.
The chrome is used in the processing of skins in which 65% is consumed during
the process while 35% goes waste. The presence of chrome in the discharged
water of tanneries is hazardous for public health as its excessive use can cause
severe skin diseases.To minimize the danger we have water treatment plant to
purify water to its maximum possible level.
We believe to contribute in safe and healthy environment. Super Tannery is an
eco friendly tannery.
6 Composite
waste
water
including
washing
(raw to
finish)
30-40 Alkaline, colored
contains soluble
proteins,
chromium, high
TDS & Cl,
sulfides and SS

29. 29
Chemically enhanced primary treatment (CEPT) is a technology that uses coagulants for
enhanced pollutants removal at the primary stage of the wastewater treatment. This paper
presents the detailed characteristics of tannery wastewater. It also explains effectiveness of
CEPT in removing pollutants from tannery wastewater using various metal salts. The
results of this study demonstrated that the tannery effluent had high concentrations of
organic matter, solids, sulfates, sulfides and chromium. Alum, ferric chloride and ferric
sulfate were tested as coagulants using jar test apparatus. Alum was found to be the
suitable coagulant for tannery wastewater in a doserange of 200-240 mg/L as Al2(SO4)3.
With alum, percentage removal efficiency for turbidity, total suspended solids (TSS).
The word "electro coagulation" (EC) will be sometimes used with "electro floatation"
(EF) and can be considered as the electro coagulation/flotation (ECF) process.Through
the process ofelectrolysis, coagulating agents such as metal hydroxides are produced.
When aluminum electrodes are used, the aluminum dissolves at the anode and hydrogen
gas is released at the cathode. The coagulating agent combines with the pollutants to form
large size flocks. As the bubbles rise to the top of the tank they adhere to particles
suspended in the water and float them to the surface. In fact, a conceptual framework of
the overall ECF process is linked to coagulant generation, pollutant aggregation, and
pollutant removal by flotation and settling when it has been applied efficiently to various
water and wastewater treatment processes.
This process ofpurifying wastewater at primary level can be shown as lab level. We have
performed it as follows.

30. 30
Objective: - To analyze the following parameters after Primary Treatment of Tannery
Effluent, i.e.
1. Total Suspended Solids in treated water
2. Presence Of Chromium VI+
3. pH of the water after treatment
1. To Study The TSS
Material Required: A sample of 250 ml of water before treatment.
Lab Reagents: H2SO4 , polyelectrolyte, alum
Procedure: -
 We have collected 250 ml of water before treatment & keep that in a beaker.
 Then we balanced the pH up to 7.0 approx by adding acid & more water. The final
volume of neutralized water is now 400 ml.
 Then we add 1 gm of Alum, polyelectrolyte & separate the clean water as the
sludge sits down at bottom.
 Then we filtered 1 part say 25 ml of this clean water in a glass dish named DISH 7
& Tookanother part of 25 ml directly without filtering that named DISH 3.
 Gave both of them water bath until they become dry.
 Then measure the amount of Total solid content in DISH 3 & Total Dissolved
Solids in DISH 7.
 The final readings until steady state reached has been taken as
Observation & Calculations:-
Total weight of DISH 3= 37.301 gm
Empty dish weight= 36.735 gm
TOTAL SOLIDS (TS) weight = 0.566 gm

31. 31
In ppm,
TS =Dry residue*1000*1000/25(volume taken)
So, TS = 0.566*1000*1000/25
TS = 22640 mg/l
Total weight of DISH 7 = 36.328 gm
Empty dish weight= 35.768 gm
TOTAL SOLIDS (TDS) weight= 0.56 gm
TDS =Dry residue*1000*1000/25(volume taken)
TDS = 0.56*1000*1000/25
TDS = 22400 mg/l
Now,
TOTAL SUSPENDED SOLIDS = Total solids – Total Dissolved solids
= 22640-22400
=240 mg/l
Result : - TSS in water after treatment is 240 mg/l
2.To Study The Presence of Chromium VI+
Material Required: A sample of 10 ml of water after treatment.
Lab Reagents: N,N,Diphenyl Carbazide, Acetone, Nitric Acid, ethanol, H3PO4
Glass Wares :- Test Tubes , 100 ml Volumetric flask,).5-10 ml pipette, Reagents bottle
Procedure: -
 We have taken a sample of 10 ml treated water.
 Then add 1 ml nitric acid.
 Add 2-3 drops of diphenyl Carbazide solution.

32. 32
 If pink color appeared Chromium VI+ present in the solution. presence of pink
color indicates the above limit of chromium VI.
 If color doesn’t change then chrome VI is in below the limit.
 If presence of chrome VI is above the limit then we’ll analyze it by Photo
spectrometer of wavelength 540 nm.
Observations:-
No pink color appears in the sample of treated water.
Conclusion: -
Our sample has chrome VI below the limit.
To Cross-Check our reagents: -
 We have taken K2Cr2O7 & dilute it in 1:1000 dilutions & check it the same way
mentioned above by indicator.
 Re-check it in 1:2000 & 1:3000 dilutions.
 Purple, pink & light pink color appears respectively.
3. The ph of treated water is 7.6

33. 33
Possibilities of Hexavalent Chromium Generation and Plausible
Preventive and Corrective Measures
Introduction
Chromium is the 24th element in the periodic table with an atomic weight of 52.
Chromium is the 21st most abundant element in the earth’s crust 1. The toxicity and
mutagenity of hexavalent chromium is well known. Exposure to compounds of hexavalent
chromium can cause skin allergies, dermatitis and ulcerations. These compounds can
cause perforations of nasal septum and bronchial carcinoma as 2,3. Trivalent and
hexavalent chromium are in mutual dynamic equilibrium. Trivalent chromium is less
permeable in whole cells and has lower redox potential compared to hexavalent chromium
and hence less toxic. Due to its high mobility and toxicity hexavalent chromium gain more
importance than trivalent chromium. In tanning chromium is used as a tanning agent in the
form of basic chromium sulphate with about 33% Basicity. The unreduced chromium in
the basic chromium sulphate is one of the sources of hexavalent chromium. Apart from
the direct source of chromium, trivalent chromium present in the leather after tanning may
undergo oxidation induced by various substances, chemicals and factors. Because of the
toxicity associated with hexavalent chromium, restrictions have been enforced to
minimize the presence of hexavalent chromium in leather and leather products. Therefore,
minimizing the possibility of chromium VI during manufacturing processes and
scavenging the hexavalent chromium that is generated during the process gain much
importance to the tanners. This paper deals briefly with the standards pertaining to
chromium VI, possible generation and its prevention and tools to scavenge chromium VI
formed.
Requirements
The presence of Chromium (VI) is one of the parameters of EN420 and of European Eco-
label for footwear. Various limit levels prescribed by different institutions are presented
hereunder.

34. 34
Table 1: Specifications forCr (VI)
Specification / Label Application Limit
EN 420: 1998 Standard Leather Protective Gloves 2 mg/kg
European Eco-label Footwear 10 mg/kg
Toxproof Textiles, Leather Undetectable
(TUV - Rheinland) label
Öko-tex 100 Label Textiles, Leather Undetectable
SG Label Textiles, Leather, Paper, Undetectable
Wood
LGR Label Leather Undetectable
Chromium (VI) – the source
It is essential to identify the possible sources ofCr(VI) and the possible generation of the
same during the leather and productmanufacturing process.
 The possible direct sources of Cr(VI) are the Basic Chromium Sulfate (BCS) used
as a tanning agent, certain class of metal complex dyes and inorganic pigments.
Particularly in the case of pigments based on lead chromate is a possible sourceof
hexavalent chromium.
 Unreduced chromium present tin the leather auxiliaries are the direct sourceof
Cr(VI). Apart from the direct sources many tools, substances, auxiliaries, chemicals
and process parameters could contribute significantly to the conversion of trivalent
chromium into hexavalent chromium.
 Oxidation of Cr(III) to Cr(VI) by oxygen in air during the processes carried out at
higher pH in leather and footwear manufacturing process is an important cause of
Cr(VI) generation.

35. 35
 Some of the possibilities of generation of Cr(VI) are presented below
1. Neutralization
Chromium (III) undergoes oxidation into Chromium(VI) in presence of strong oxidizing
agent in acidic condition. Oxidation can also occurat higher pH with the help of mild
oxidizing agents. The aforesaid conditions prevail during neutralization of wet blue
leather. Direct correlation between the final pH and the Cr(VI) conversion could not be
established. However it was reported that there was a clear correlation between the
neutralization pH and Cr(VI) generation in the wet blue. Cr(VI) was found to increase
with the increase in neutralization pH. But it was reported that the leathers after finishing
did not show the presence of Cr(VI)8. It was concluded that the Cr(VI) content was
independent of neutralization pH. Whereas it was also reported that regardless of the
chemical chosen for neutralization the Cr(VI) in the finished leathers after heat treatment
were found to be in direct proportion with the pH of neutralization. Therefore it can be
construed that there is a direct correlation between the Cr(VI) content in leather and the
neutralization pH 9. It was also found out that in the extreme conditions such as carrying
out neutralization at 80oC for 24 hrs showed presence of Cr (VI) 10.
2. Ammonia Treatment
Treatment of crusts prior to dyeing with ammonia, sodium bicarbonate, cationic
auxiliaries aiming better leveling and penetration may promote the oxidation of Cr (III). It
was reported that the Ammonia and sodium bicarbonate treated samples when heated to
80oC for 24 hours showed the presence of Cr (VI).
3. Thermal and Photo-ageing
Thermal ageing or exposure to UV light can induce the formation of large amounts of
Cr(VI). It is also reported that the natural light or UVA light (UV light produced bylamps
of 366 nm) can induce the formation of Cr (VI)11.
4. Fatliquors
Fatliquors have a significant role in the formation of Cr(VI). The kind of fatliquors known
to cause the formation of Cr(VI) are sulfated fish oils, sulfited fish oils, fatliquoring
products with single or multiple unsaturated fatty acids either free or esterified. The free
radicals that are released by the unsaturated lipids in presence of UV light can
significantly cause the formation of Cr(VI). Sulphited vegetable oils were also found to
cause Cr(VI) formation.
5.Adhesives Used in Product making
There appear possibilities of Cr(VI) formation when alkali Glue is used for binding (in the
Shoe making). The levels of Cr(VI) in leather increased significantly after using the said

36. 36
adhesive and heat setting. The degree of conversion of Cr(VI) reported to be higher if the
extractable Cr(III) level is high ie more than 50 mg/kg.
Avoidance and Mitigation
The background of the possible sources of Cr(VI) and possibilities of Cr (VI) formation
torches the pathway of solution to the problem. It is obvious and principally important to
avoid the direct sources of Cr(VI).
 The BCS used for tanning needs to be screened for the level of Cr(VI) and avoided
if found to contain significant mass of Cr(VI).
 The process ofChrome tanning needs to be controlled and monitored so as to
minimize the level of leachable chromium. As more amount of leachable chromium
enhances the Chromium conversion into Cr(VI).
 Similarly the Dyes and Pigments shall be chosenfor processingonly if they contain
no or undetectable levels of Cr(VI). The yellow colored anionic pigments that are
based on chromate are most likely to contribute to Cr(VI). The problem becomes
much serious if the pigment contains Ammonia or Carbonates. It shall be ensured
that such pigments are screened and avoided for use in the finishing operation.
 Fatliquors including synthetic or natural, especially fish oil based fatliquors with
single or multiple unsaturated fatty acids shall be avoided.
 Exposure to direct sunlight for drying may be avoided.
 Alkaline glue (as adhesive) shall be avoided in shoe making operations.
The points to be pondered for the mitigation of Cr(VI) are presented below.
 It is preferable to use neutralizing auxiliaries with reduction capability in Neutralization
and wetting back of crusts.
 Treatment with vegetable tanning agents proved to reduce the presence of Cr(VI). The
vegetable tanning agents that show marked influence in reducing the levels of Cr(VI)
are Wattle, Quebracho, Chestnut and Tara. Tara however understood to be the bestin
the said characteristic among all. Even treatment with 1% of Tara proved to reduce the
risk of presence of Cr(VI) significantly.
 Reducing agents such as sodium bisulfite, Sodium metabisulfite13 may be used in the
final washing of leather. However it may please be noted that such treatments may alter
the shade and colour intensity of the leather and hence accordingly the process of
dyeing needs to be restandardised.

37. 37
Objective:-To check the purity of recovered BCS From BCS Recovery Plant
Glassware’s:- iodine flask 250 ml with stopper, burette (0-50 ml), Hot Plate,
Reagent Bottle
Lab Reagents:-
 Fusion Mixture of acids HClO4,HNO3,H2SO4 in 12:5:3
 Potassium Iodide 10 ml of 10%
 Titration against N/10 Sodium ThioSulphate
 Starch Powder
Procedure:-
 Take 10 Ml colored liquor
 Make it dilute
 Take 5 ml of this diluted liquor & add 1 NaOH pallet & H2O2 as indicator
 Then Green to wine color appears.
 Make it dry on Hot plate.
 Then make aqueous solution of it by adding 50 ml water & add 10 ml HCl to make
it acidic & coolit & add KI.
 Now titrate it against N/10 Sodium ThioSulphate.
 Note the reading till the sky blue color appears.
Properties of BCS
Cr2O3= 23.0±0.2
Basicity= 33±2.0
pH= 3.0±0.2
Calculations:-
Consumption of hypo = 2.3 ml
Cr2O3 content % by volume = (0.002534* 2.3 ml * 0.1 *250*100/ (5*10)

38. 38
= 0.29% by volume
In 1 litre= 2.9 g/l Cr2O3
& 290 g/100 litres Cr2O3
100 kg BCS = 23 kg Cr2O3
So in 1.26 kg BCS= 0.29 kg Cr2O3
Result: - 1.26 kg BCS= 0.29 kg Cr2O3