Principles of Non Ferrous

Extraction MetallurgyExtraction Metallurgy

Date 18th Aug, 2014

In last class• High temp vs low temp process

• High pressure vs low pressure process

• Combination of above HT+HP, LT+HP, LT+ LP

• Heterogeneous and Homogenous reactions• Heterogeneous and Homogenous reactions

• Reaction at Interface

• Chemical and physical adsorption

Adsorption

In pyrometallurgical processes

• We are much concerned about chemical

adsorption (chemisorption)

• Bond formation exists between species and

interfacial layer (sometimes also termed as interfacial layer (sometimes also termed as

substrate)

• Due to chemical in nature heat is evolved

which means bond has formed

• If bond has formed than it is irreversible

Adsorption

• Saturation of chemi adsorbed layer takes place

when layer by layer chemi adsorption takes

place which further delays the chemis

adsoprtion of approaching layeradsoprtion of approaching layer

• To understand the adsorption process we

have to invoke a concept by assuming process

taking place at constant temperature

Langmiur adsorption isotherm

• If adsorption is taking place at constant temperature than it is known as adsorption isotherm

• The simplest one of such isotherm is Langmiur• The simplest one of such isotherm is Langmiuradsorption isotherm where you consider no mutual interaction among the adsorbed layer and molecular being adsorbed

• Langmiur adsorption isotherm is called ideal adsorption isotherm and is applicable to chemisorption of ideal gas on solid surface

Langmiur adsorption isotherm

• We don’t consider any mutual interaction

among adsorbed layer??

• If interaction takes place among adsorbed

layer than due to such interaction there will layer than due to such interaction there will

be rise or drop in interfacial temperature.

• Such rise in temperature will disturb the

criteria of invoking isotherm

Refining process (Three approaches)

(1)Creation of proper thermodynamic and kinetic conditions for transfer of impurity away from metallic phase during extraction process itself.

(2)Production of pure metal compound for subsequent reduction

(3)Production of impure bulk metal during extraction and subsequent purification by refining methods

Refining process (Three approaches)

• Creation of slag and achieving good slag metal

separation is and example for (1)

• Large number of reactive metals and rare

earths are prepared using halides is and earths are prepared using halides is and

example for (2)

• Traditional mode of purification to produce

large quantities (3) ex: Aluminium/Copper

Purification process

• Interestingly in all the purification process more

than one phase is involved (Heterogeneous)

• The over all process depends on transfer of

impurities from one phase to anotherimpurities from one phase to another

• Methods of purification widely employed

(a) Physical methods (Unit Operation)

(b) Chemical methods (Unit Process)

(c) Electrochemical methods (Unit Process)

Selective Distillation of Impurities

(Example of Physical Process)• TA , BP of A

• TB, BP of B

• TA< TB, which means on heating A vaporized more easily

• Evacuation of reaction chamber helps because it • Evacuation of reaction chamber helps because it allows working at lower temperature?? (Next slide)

• Volatile zinc can be removed from liquid lead by vacuum distillation?? (next slide)

• BP of Zinc 907 deg C, BP of Pb 1740 deg C

• MP of Zinc 419 deg C, MP of Pb 327 deg C

Vapor pressure curves

Vapor pressure curves

Questions

• When to apply selective distillation?

• What about high vapor pressure metals. Can

we apply selective distillation? If we can apply

than what challenges we have?than what challenges we have?