Reconciling Growth, People and the Environment

F0_0244_0000_Photo17Despite the fact that quarrying in some form or other has been carried out since the Stone Age and counts – along with the procurement of food and housing- as one of the basic activities of human beings-, people still tend to regard this kind of activity with distrust and fear its effects on the local environment. The Gypsum Industry prides itself on its deep commitment to the interests of the community. An established tradition in the responsible use of natural resources and in the rehabilitation of depleted gypsum quarries is now matched by an active stance in the recovery and reprocessing of Gypsum waste.

Extracting and Processing Natural Gypsum

Gypsum/Anhydrite are produced from open-cast mines or underground mines using pillar and stall mining methods that give extraction rates of up to 75%.

Gypsum is normally only screened to remove ‘fines’ (mainly mudstones), then crushed and finely ground. Gypsum/Anhydrite for cement manufacture is supplied in crushed form for further fine grinding with cement clinker.

When Gypsum (CaSO4,2H2O) is ground to a powder and heated at 150° to 165° C, three-quarters of its combined water is removed producing hemi-hydrate plaster (CaSO4,1/2H2O), commonly known as the ‘Plaster of Paris’. When this powder is mixed with water the resulting paste sets hard as the water recombines to produce Gypsum again. This process can be repeated almost indefinitely, with important implications for recycling.

Sourcing and Processing FGD Gypsum

FGD Gypsum is an alternative to natural Gypsum that comes from the flue gas desulphurisation plant (FGD) of the power station industry. FGD Gypsum is the end product of a wet purification procedure with natural lime, that essentially forms according to the same laws as natural Gypsum–but in a speeded-up process taking only a few hours.
FGD Gypsum has a higher purity (Gypsum content of 96%) than most natural Gypsum (80%). This means that lower quality Gypsum can be blended with high purity Desulphogypsum, allowing material that would not have been mined in the past to be classified as exploitable reserves.