What Is Gypsum?

A Soft White or Gray Mineral Consisting of Hydrated Calcium Sulfate. It Occurs Chiefly in Sedimentary Deposits and Is Used to Make Plaster of Paris and Fertilizers, and in the Building Industry.

What Is the Composition of Gypsum?

Gypsum is a mineral composed primarily of calcium sulfate dihydrate (CaSO4·2H2O). It is a soft mineral that forms as the result of the evaporation of saline water.

The chemical formula of gypsum indicates that each unit of the mineral contains one calcium atom (Ca), one sulfur atom (S), four oxygen atoms (O), and two water molecules (H2O).

To summarize, the composition of gypsum is:

• Calcium (Ca)
• Sulfur (S)
• Oxygen (O)
• Water (H2O)

The Formation and Extraction of Gypsum

Gypsum is formed through the process of evaporation of saline water over an extended period. It typically occurs in areas with dry climates where there is an abundance of calcium and sulfur. The process of gypsum formation involves the following steps:

• Source of Calcium and Sulfur: Gypsum can originate from a variety of sources. It is commonly formed from the dissolution of calcium-containing minerals like limestone (calcium carbonate) or by the reaction of sulfur-rich sediments with groundwater.
• Water Evaporation: When water containing dissolved calcium and sulfate ions evaporates or undergoes significant reduction in volume, the concentration of these ions increases. This higher concentration leads to the precipitation of gypsum as the water becomes saturated with calcium sulfate.
• Gypsum Crystal Formation: As the water evaporates, the calcium and sulfate ions combine to form gypsum crystals. The crystals may vary in size and shape depending on the specific conditions of the environment in which they form.
• Extraction of gypsum typically involves mining or quarrying. The process may vary depending on the location and the nature of the gypsum deposit, but it generally follows these steps:
• Exploration and Site Preparation: Geological surveys and analysis are conducted to identify potential gypsum deposits. Once a suitable deposit is found, the site is prepared for extraction, including obtaining necessary permits and clearing the area if required.
• Mining or Quarrying: Gypsum deposits can be extracted through mining or quarrying methods. In underground mining, tunnels or shafts are dug into the earth to reach the gypsum deposit. In open-pit mining, the gypsum deposit is exposed at the surface, and it is extracted using heavy machinery.
• Crushing and Grinding: The extracted gypsum is usually crushed and ground into smaller particles to facilitate further processing. This step helps in increasing the surface area of the gypsum, making it easier to handle and enhancing its reactivity in subsequent applications.
• Calcination: The crushed and ground gypsum is subjected to a process called Calcination, which involves heating the gypsum at high temperatures to drive off the water molecules present in the mineral. This results in the conversion of gypsum into its hemihydrate form, known as plaster of Paris (CaSO4·0.5H2O).
• Further Processing: The calcined gypsum, or plaster of Paris, can be further processed into various forms depending on its intended use. It can be molded into desired shapes, used as a binder in construction materials, or converted into gypsum board or drywall.

Gypsum as a Key Ingredient in Plasterboard and Drywall

Gypsum is indeed a key ingredient in the production of plasterboard and drywall. Plasterboard, also known as gypsum board or wallboard, is a widely used construction material for interior walls and ceilings.

Here's how gypsum is used in the production of plasterboard:

• Gypsum Extraction and Processing: Gypsum is extracted from mines or quarries and processed to remove impurities. The extracted gypsum is then crushed, ground, and heated in a process called calcination to convert it into the hemihydrate form of calcium sulfate (plaster of Paris).
• Core Production: The calcined gypsum is mixed with water and additives to form a slurry. This slurry is then poured onto a continuous sheet of paper or other facing material. Another sheet of paper is placed on top, and the three layers are sandwiched together.
• Drying and Setting: The plasterboard assembly is passed through a series of rollers to remove excess water and to ensure uniform thickness. The wet plasterboard is then cut into desired lengths and transferred to a drying chamber where the remaining moisture is removed. During the drying process, the gypsum sets and hardens, forming a solid core.
• Facing Attachment: Once the plasterboard is dry, it is trimmed to precise dimensions and the manufacturer's logo is printed on the back. Optional additives may be applied to enhance properties such as fire resistance or sound insulation. The finished plasterboard is then ready for use.

Plasterboard offers several advantages in construction, including ease of installation, versatility, and fire resistance.

It provides a smooth, flat surface for finishing with paint, wallpaper, or other decorative materials. The gypsum core in plasterboard contributes to its strength, durability, and sound insulation properties.

Drywall is another term commonly used to refer to plasterboard, particularly in North America. It is essentially the same material—composed of a gypsum core sandwiched between paper facings—but may be referred to as drywall due to its use in creating interior walls and ceilings without traditional wet plaster applications.