SUPER TANNERY INDIA LTD.
PREPARED BY :
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.
Casual and Formal
Safety and Casual
Leather is a durable and flexible material created by
the tanning of animal raw hide and skin, often cattle hide.
It can be produced through manufacturing processes
ranging from cottage industry to heavy industry.
Leather is used for various purposes including clothing
(e.g. shoes, hats, jackets, skirts, trousers and
belts), bookbinding, leather wallpaper, and as a furniture
Buffalo, goats, alligators, snakes , ostriches, kangaroos,
oxen, and yaks may also be used for leather.
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.
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
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.
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 chemical reaction involve here is CaO + H2O + Na2S → Ca(OH)2 + NaOH +
Ca(OH)2 : swells the hide
NaHS: hair removal
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.
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
Mostly (NH)4SO4 is used in industry as it has less ammoniacal nitrogen content
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 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
Chrome-tanned leather, invented in 1858, is tanned
using chromium sulfate and other salts of chromium. It is
more supple and pliable than vegetable-tanned leather and
does not discolor or lose shape as drastically in water as
vegetable-tanned. It is also known as wet-blue for its color
derived from the chromium. More esoteric colors are
possible using 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
Main advantages of chrome tanning
Quick and easy to produce, usually only taking up to a
Water can roll off the surface easily with appropriate
retanning and finishing processes
Soft and supple to the touch
It is possible to obtain leather with a stable colour
It is cheaper to buy than vegetable tanned leather, which
means it is also easier to find
It has a high degree of thermal resistance
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 corrected grain leather.
Furthermore to modify the surface properties (shade, lustre, handle, etc.).
Finishing materials may be classified into 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
Chemical Finishing: - involves the application of a film, natural or synthetic by
using curtain coaters, roller coatings and spraying.
Sr. No Characteristic of leather/
parameter of testing
Requirements Units Test method
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)
6 Water Penetration 60 Min Minutes IUP-10/DIN53338
7 Water Absorption 30 Max
(After 2 Hrs)
8 Water Vapour Permeability 1.0 Min Mg.cm2/hr IUP-15/DIN53333
9 Water Vapour Co-Efficient 80 Min Cm Hg
10 Heat Resistance 180 Max Temp C IUP-13
11 Color Fastness Grade-3
Rubs Min 50
12 Grain Distention Of Crackness 7.0 Min mm IUP-12/DIN53324
PHYSICAL PROPERTIES OF FINISHED LEATHER
(BUFFALO GRAIN BARTON)
Characteristic of leather/
parameter of testing
Requirements Test method
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
5 Determination Of Nitrogen &
1.4 max IUP-10/DIN53308
6 Determination Of Water
2.0 max IUP-6/DIN53307
7 Determination Of Chromium
2.5 max IUP-8/DIN53309
8 Determination Of pH 3.5 max IUP-11/DIN-EN/ISO4045
CHEMICAL PROPERTIES OF FINISHED LEATHER
(BUFFALO GRAIN BARTON)
NOTE: - Except pH all requirements are in %.
WASTE GENERATION IN TANNERIES
Tanning industry is one of the oldest industries in the world. It is typically
characterized as pollutants generated industries which produce wide 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, specific pollutants (sulfide, chromium, chloride, sodium and
other salt residues) and heavy metals etc
Water usage and waste water discharge
Raw to Wet Blue= 25-30 l/kg of hide.
Raw to finish= 30-40 l/kg of hide
Modes of operation Water
Chemicals used General Constituents
of waste water
1 Soaking Pits/ paddles 9-12 Wetting,
matters & high
amount of Cl
2 Liming Pits/ paddles 2.5-4.0 Lime & Na2S Highly alkaline,
amount of sulphides,
hair pulp and
3 Deliming Pits/ paddles/ drums 2.5-4.0 Ammonium salts,
high amount of
organic matters &
Characteristics of Wastewater
4 Pickling &
Drums 2.0-3.0 Common salt,
amount of trivalent
and Cl, acidic dyes
& oil emulsion
5 Dyeing & fat
Drums 1.0-1.5 Dyes & fatty
30-40 Alkaline, colored
TDS & Cl, sulfides
Chromium (VI) – the source
It is essential to identify the possible sources of Cr(VI) and the possible generation
of the same during the leather and product manufacturing 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 source of
Unreduced chromium present tin the leather auxiliaries are the direct source of
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
Some of the possibilities of generation of Cr(VI) are presented below
2. Ammonia Treatment
3. Thermal and Photo-ageing
4. Fat liquors
5. Adhesives Used in Product making
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 of Chrome tanning needs to be controlled and monitored.
• Similarly the Dyes and Pigments shall be chosen for processing only if they
contain no or undetectable levels of Cr(VI).
• Fat liquors including synthetic or natural, especially fish oil based fat liquors
with single or multiple unsaturated fatty acids shall be avoided.
• Exposure to direct sunlight for drying may be avoided.
The Various Purity tests done there are:-
1. To determine the Chromium oxide (Cr2O3)
Amount of Cr2O3 3.1675 %
2. To check the purity of recovered BCS From BCS Recovery Plant
Result: 1.26 kg BCS= 0.29 kg Cr2O3
3. To analyze the following parameters after Primary Treatment of Tannery
Total Suspended Solids in treated water
Presence Of Chromium VI+
pH of the water after treatment
TSS in water after treatment is 240 mg/l
No pink color appears in the sample of treated water. So below the limit.
The ph of treated water is 7.6