GYPSUMGYPSUM

In nature : Gypsum RockIn nature : Gypsum Rock

Pure gypsum rock : CaSOPure gypsum rock : CaSO44.2H.2H22OO

Impurities : MgO, AlImpurities : MgO, Al22OO33, Fe, Fe22OO33, SiO, SiO22, , CaCOCaCO33, MgCO, MgCO33......

GYPSUMGYPSUM

PRODUCTION STEPSPRODUCTION STEPS ExcavatingExcavating Crushing (Crushing (~~25 25

mm diameter)mm diameter) GrindingGrinding Heating Heating

(calcining)(calcining) Cooling and Cooling and

PulverizingPulverizing Marketing in Marketing in

BagsBags

CALCINATIONCALCINATION Gypsum rock wahen heated to 100-190Gypsum rock wahen heated to 100-190°°C C

looses ¾ of its water.looses ¾ of its water.

CaSOCaSO44.2H.2H22O O → → CaSOCaSO44..½½HH22OO + 3/2 H + 3/2 H22OO

Plaster of ParisPlaster of Paris

This is low burning process and named as This is low burning process and named as INCOMPLETE CALCINATIONINCOMPLETE CALCINATION..

When calcination is carried out at temperatures When calcination is carried out at temperatures above 190above 190°°C all water is removed.C all water is removed.

CaSOCaSO44.2H.2H22O → O → CaSOCaSO44 + 2H + 2H22OO

gypsumgypsum anhydriteanhydrite

This is high-burning process & This is high-burning process & COMPLETE COMPLETE CALCINATIONCALCINATION..

Both of these products form gypsum Both of these products form gypsum rock by recombining with water.rock by recombining with water.

CaSOCaSO44..½½HH22O + 3/2HO + 3/2H22O O → CaSO→ CaSO44.2H.2H22OO

CaSOCaSO44 + 2H + 2H22O → CaSOO → CaSO44.2H.2H22OO

Calcination process is carried out in two Calcination process is carried out in two types of kilns.types of kilns.

Kettle KilnsKettle Kilns Rotary KilnsRotary Kilns

KETTLE KILNKETTLE KILN

HEAT

FIRE BRICK

~ 2.5-3 cm

~ 2-3 m

DISCHARGE

GYPSUM ROCK

MIXER

ROTARY KILNROTARY KILN

GYPSUM PLASTERSGYPSUM PLASTERS Obtained by Incomplete Calcination Obtained by Incomplete Calcination

(CaSO(CaSO44..½½HH22O)O)

1.1. Plaster of Paris : is formed by Plaster of Paris : is formed by incomplete calcination at 100-190incomplete calcination at 100-190°°C. C. No admixtures are found.No admixtures are found.

2.2. Hard Wall PlasterHard Wall Plaster

Plaster of Paris + Admixtures (Glue, Plaster of Paris + Admixtures (Glue, Sand...)Sand...)

Obtained by Complete Calcination Obtained by Complete Calcination (CaSO(CaSO44))

1.1. Flooring Plaster (CaSOFlooring Plaster (CaSO44 with no with no impurities)impurities)

2.2. Hard Finish Plaster (CaSOHard Finish Plaster (CaSO44 + Al + Al22(SO(SO44))33))

(CaSO(CaSO44 + Na + Na22BB44OO77))

PROPERTIES & USES OF PROPERTIES & USES OF GYPSUM PLASTERS GYPSUM PLASTERS

Plaster of ParisPlaster of Paris– Setting time Setting time ~~5-20 min.5-20 min.– Used for sculpturing, ornamental work, Used for sculpturing, ornamental work,

small repair worksmall repair work

PROPERTIES & USES OF PROPERTIES & USES OF GYPSUM PLASTERS GYPSUM PLASTERS

Hard Wall PlasterHard Wall Plaster– Setting time Setting time ~~1 hr1 hr– Compressive strength Compressive strength ~~7 MPa7 MPa– Admixtures result in increased plasticity & Admixtures result in increased plasticity &

setting time & reduced shrinkagesetting time & reduced shrinkage– Can be used for plastering wallsCan be used for plastering walls– Production of prefabricated structural Production of prefabricated structural

unitsunits– Masonry bricks & blocksMasonry bricks & blocks

Flooring, Hard Finish PlasterFlooring, Hard Finish Plaster– Setting time Setting time ~~1-16 hrs1-16 hrs– Compressive strength Compressive strength >> 7 MPa 7 MPa– Can be used for producing prefabricated Can be used for producing prefabricated

units, masonry bricks & blocks & flooring units, masonry bricks & blocks & flooring & pavement bricks & tiles.& pavement bricks & tiles.

PROPERTIES & USES PROPERTIES & USES OF GYPSUM PLASTERS OF GYPSUM PLASTERS

Gypsum often serves as a fire proofing Gypsum often serves as a fire proofing material even though its strength is material even though its strength is destroyed by long continuous heat. It destroyed by long continuous heat. It forms a powder covering the surface forms a powder covering the surface which acts as an effective insulator.which acts as an effective insulator.

Gypsum products tend to Gypsum products tend to disintegrate when exposed to disintegrate when exposed to moisture. Therefore, they should moisture. Therefore, they should not be used for exterior work & not be used for exterior work & for moist interiors. for moist interiors. (NON-HYDRAULIC)(NON-HYDRAULIC)

PROPERTIES & USES PROPERTIES & USES OF GYPSUM PLASTERS OF GYPSUM PLASTERS

BY-PRODUCT GYPSUMBY-PRODUCT GYPSUM

PhospogypsumPhospogypsum – Major by-product – Major by-product of phosporic acid productionof phosporic acid production

phosphate + sulfuric acid --> fertilizer + gypsumphosphate + sulfuric acid --> fertilizer + gypsum

DesulfogypsumDesulfogypsum – Obtained from the – Obtained from the desulfurization of combustion gases desulfurization of combustion gases in coal burning power plants in coal burning power plants (Harmful SO(Harmful SO22 gas is turned into gas is turned into CaSOCaSO44.2H.2H22O O