A story that began long time

ago…..

A story that began long time

ago…..

A story that began long time

ago…..

A story that began long time

ago…..

PRESENTATION ON

INORGANIC SALTS USED FOR TANNING

CHROMIUM SALT, IT’S BEHAVIOUR IN

SOLUTION, OXIDATION RATE AND

COMPLEX FORM OF TRI VALENT TITANIUM

INORGANIC SALTS USED FOR:

Tanning

Curing

Soaking

Liming and Un-hairing

Washing

Deliming

Pickling

Chrome Tanning

What is Chromium?

Chromium Salts

Oxidation Rate

Behaviour of Chromium Salts in Different

Solutions

Complex Form of Tri Valent Titanium

Question and Answer Session

A BRIEF IN BANGALI....

I C E B R E A K I N G . . . . . . . . .

Phase -1

Tanning

The process of making leather from raw h/s.

The word “Tanning” derives from “Tannin” an

acidic chemical compound.

It includes some primary and intermediate

stages.

In the stages different inorganic salts are used.

Curing

Curing means short time conservation of raw h/s

as the decay of hides quality start as soon as flaycompleted.

It’s required to preserve the raw skin for short period.

In curing process we may follow one of these steps:

Wet-salting

Dry salting

Drying

Brining

Freezing

Curing The salts are used in curing is might be these types:

Vacuum salt: 99.9% pure and size less than 1 mm.

Granular salt: 99.9% pure and size is 2-4 mm.

Rock salt: Mined and crushed to the needed crystal

dimensions.

Marine salt: Artificially prepared by evaporation

process.

Khari salt: Strictly this material cannot be said as salt.

Curing

Salt list is given below:

Sodium Chloride – NaCl

Sodium Carbonate - Na2CO3

Sodium penta chlorophenate - C6H5Cl5ONa

Sodium silicofluorides - Na2SiF6

Sodium sulfite - Na2SO3

Beside Naphthalene is also used in curing.

Soaking

Restoration of natural swollen condition of hides and

removal of dirt, soluble protein and curing agent is

known as soaking.

Actually it’s a process of rehydration.

In soaking salts are used given below:

Sodium carbonate - Na2CO3

Sodium Sulfide - Na2S

Sodium Tetra-sulfide – Na2SO4

Amonia Containing salts

Enzymes and detergent are also used in soaking

process.

Soaking

Sodium carbonate

Liming & Unhairing

Treatment of soaked hides and skins with the milk of

lime with or without addition of salts.

In this process the liming chemicals also destroy the

hair and epidermis layer completely.

Thus the unhairing process end.

Salts are used listed following:

Sodium Sulfide - Na2S

Sodium Hydrosulfide – NaHS

Washing

Washing is the step to wash the half processed raw

skins for the next method.

For washing Sodium Meta-bisulphate is only used.

As example:

Sodium meta bisulfate - Na2S2O5

De-liming After liming the unhaired and fleshed hides and

skins known as pelts, are taken for De-liming.

During this step huge chemicals are used.

Both salts and acids are frequently used in the

step:

Ammonium Chloride - NH4Cl

Ammonium Sulfate - (NH4)2SO4

Ammonium Sulfa mate - (NH3)2SO3

Sodium Bisulfate - NaHSO4

Sodium bisalfite - NaHSO3

Calcium Borate - Ca3 (Bo3)2

Calcium Lactate - Ca(CH3CHOHCOO)2

Calcium Sulfate - CaSO4

De-liming

Ammonium chloride

De-liming

Ammonium sulfate

Bating & Drenching

No salts have used in this step. Dung is used in

this steps.

Pickling & Degreasing

The treatment of de-limed or bated pelts with a

solution of acid and salt.

It has done both in chrome and vegetable tanning.

Salts for pickling is,

Common salt – NaCl

Sodium Sulfate – NaSO4

Sodium Formate - HCOONa

Sodium Acetate – CH3COONa

** Degreasing doesn’t need any salt.

Pickling &

Degreasing

Sodium sulfate

Chrome Tanning

This is the final status of a pelt when it becomes a

leather.

In chrome tanning following salts are used:

* Tri-valent chromium salts

* Sodium chloride –NaCl

* Sodium sulfate - – NaSO4

* Chromium hydroxyl Sulfate

* Chromium sulfate – CrSO4

* Sodium bicarbonate

After tanning Sodium bicarbonate is used.

Chrome

Tanning

Chromium sulfate

Phase - 2

Chromium:

* Symbol- Cr

* Atomic number- 24

* First Identified in 1797 in France

* Chromium exhibits a wide range of OS

Chromium Salts

@ Most effective and efficient tanning agent.

@ Mostly used safe III Chromium salts.

@ Chromium salts used for tanning are:

# Chromium sulfate

# Chromium hydroxy sulfate

# Chrome alum

# Chromium acetate

# Chromium chloride

# Potassium dichromate

# Sodium dichromate

Chromium

Salts

Chromium acetate

Chromium

Salts

Sodium dichromate

Chromium

Salts

Potassium dichromate

Oxidation Rate of Chromium

Chromium is a D-Block metallic element and a reducing agent.

The electronic configuration of Cr is:

Cr(24) : Ar 3d5 4s1

Oxidation state of Chromium is:

Cr(24) : -II –I 0 +I +II +III +IV +V +VI

Oxidation Rate of Chromium

Chromium only shows negative electronic states, when it reacts with highly electro positive elements.

The most stable states are +II +III and +VI.

In this three oxidation states Chromium’s rate of reaction is higher than other oxidation states.

Chromium forms compound in oxidation state +IV but as this stage is not stable, the compounds quickly deform and reform new compounds using it’s +II oxidation state.

Behaviour of Cr Salt in Different

Solutions

Behaviour of Cr Salt in Acid

SolutionACID SOLUTION

OXIDATION STATE

+VI +V +IV +III +II +I 0

Cr O2 72- +1.33 2+3+

Cr Cr

-0.91

Cr

-0.41

+0.295

-0.74

BASIC SOLUTION

OXIDATION STATE

+VI +V +IV +III +II +I 0

Cr O 42- 3

Cr(OH) Cr2

Cr(OH)

Behaviour of Cr Salt in Basic Solution

-1.3

Complex Form of Tri Valent

TitaniumThe +4 oxidation state dominates Ti

chemistry but +3 state complex

compound are also common.

Such as:

K2NaTiF6

K3 TiF6 – Potassium hexafluorotitanate

NaTiF6 – Sodium hexafluorotitanate