Agglomerated Materials: Gypsum and Lime Production

Agglomerated Materials Defined

Stones, sand, and similar substances are materials that possess the property of adhering to other materials, forming what are known as mortar and concrete pastes. These materials are molded into their final form and subsequently harden.

Agglomerative Material Classification

Aerial Materials

These are materials that harden in the air and are not water-resistant (e.g., gypsum, aerial lime).

Hydraulic Materials

These harden both in air and in water (e.g., hydraulic lime, Portland cement).

Bituminous Materials

These are liquid or viscous hydrocarbons that harden by evaporation of their solvents or by cooling (e.g., asphalt cement).

Types of Gypsum

• Gypsum Dihydrate (CaSO₄·2H₂O): The most abundant form found in quarries.
• Gypsum Hemihydrate ((CaSO₄)₂·H₂O): Also known as Plaster of Paris.
• Anhydrite (CaSO₄): A less abundant form.

Obtaining Plaster

Thermal Conversion Process

At temperatures between 140-200 ºC, gypsum dihydrate is converted into gypsum hemihydrate through the following reaction:

2(CaSO₄·2H₂O) → (CaSO₄)₂·H₂O + 3H₂O

As gypsum dihydrate is the most abundant form in nature, it needs to be converted into hemihydrate for use as a construction material.

Gypsum Manufacturing Process

1. Extraction of Gypsum Stone

Extraction is performed using open-pit or gallery procedures, depending on the quarry's layout. Blasting with black powder is used to aid fragmentation, minimizing shredding, which is difficult due to gypsum's elasticity.

2. Crushing

Jaw crushers are used, consisting of two steel plates: one vertically grooved and fixed, and the other inclined and fixed by a pin-type joint at the top.

3. Calcination

Traditional Method

This method involves digging pits in the ground, placing larger stones in vault-like forms, and then stacking them alternately.

Industrial Processes: Boilers

Mechanical boilers, approximately 2 meters in diameter, contain a moving stirrer and scraper. Heat is supplied by flames produced from compressed gas or oil, which circulate around the bottom and sides of the boilers.

Rotary Kilns

These kilns are similar to cement cylinders but smaller, typically about 10 meters long and 1.5 meters in diameter. Calcination is achieved by applying heat to the furnace walls.

4. Grinding

This operation is performed in rotary or disintegrating mills. Rotary mills consist of two stone wheels placed horizontally, one above the other, with the upper wheel usually fixed and the lower one mobile.

Aerial Lime

Aerial lime is the product resulting from the decomposition of limestone.

Classification of Limes