The key difference between gypsum and phosphogypsum is that gypsum is a naturally occurring form of calcium sulfate, whereas phosphogypsum is a synthetic form of calcium sulfate. More specifically, gypsum is a rock-forming, soft crystal obtained by mining or quarrying, but phosphogypsum is a by-product during the production of superphosphate from phosphate rock.
Therefore, both gypsum and phosphogypsum are forms of calcium sulfate. Both these compounds contain calcium sulfate in the dihydrated form.
CONTENTS
1. Overview and Key Difference
2. What is Gypsum
3. What is Phosphogypsum
4. Side by Side Comparison – Gypsum vs Phosphogypsum in Tabular Form
6. Summary
What is Gypsum?
Gypsum is a mineral containing calcium sulfate, and it has the molecular formula CaSO4·2H2O. It is one of the most common sulfate minerals. Furthermore, it is a rock-forming mineral that can grow up to very large sizes. When we take a crystal, usually, the colour of the crystal is white or colourless, but there can be other shades of colours like grey, red or yellow too. Besides, crystals also can occur as either transparent or translucent. Of these, gypsum is a soft crystal, which can be scratched even by a fingernail. Also, it is a flexible material, and its thermal conductivity is low.
Moreover, gypsum is slightly soluble in water, and when we heat it, water will evaporate, and it can achieve the anhydride solid state again. Gypsum exists in many places all over the world (in the UK, Russia, Canada, Africa, Asia, USA and Europe). However, Gypsum is abundant in Colorado and Mexico in the USA.
Figure 01: Appearance of Gypsum
The major route of formation of this material is from precipitation of marine water. While forming the minerals, water or unwanted material can trap inside the crystal, which is the cause of different coloured crystals. Furthermore, there are three types of gypsum. They are as follows:
- Selenite
- Alabaster
- Satin spar
Selenite is crystalline in nature and is transparent or translucent. Alabaster grows into massive mineral beds. It has a light colour or lightly tinted colour due to impurities. In contrast, the satin spar is fibrous or silky in nature. We can use this material for making plaster of Paris, some cement, fertilizer (ammonium sulfate fertilizer), and as an ornamental stone. In addition to these, gypsum is also useful as manure and is a good source of sulfur. Moreover, it has the capability of becoming plastic-like when we heat it up to 175°C. This nature of Gypsum is important in producing plaster of Paris. If the content of CaSO4·2H2O in gypsum is high, it is very effective in producing fertilizer, plaster of Paris and cement. Therefore, there is a high demand for pure gypsum, which has at least 80% CaSO4·2H2O content.
What is Phosphogypsum?
Phosphogypsum refers to the hydrated calcium sulfate that forms as a byproduct of fertilizer production from phosphate rock. That is; this material forms as a side product when treating phosphate rock with sulfuric acid to get superphosphate. Furthermore, phosphogypsum contains the dihydrate of calcium sulfate. Therefore, the chemical formula for this compound is CaSO4.2H2O. That means, phosphogypsum mainly contains gypsum. However, unlike gypsum, phosphogypsum is not that much used in the construction industry.
Figure 02: Phosphogypsum Stack
Moreover, phosphogypsum shows weak radioactivity. Therefore, we have to store it carefully. The radioactivity of this material is mainly due to the presence of naturally occurring Uranium and Thorium and the daughter isotopes of these elements present in phosphogypsum.
What is the Difference Between Gypsum and Phosphogypsum?
Gypsum and phosphogypsum are hydrated forms of calcium sulfate. However, the key difference between gypsum and phosphogypsum is that gypsum is a naturally occurring form of calcium sulfate, whereas phosphogypsum is a synthetic form of calcium sulfate. Furthermore, we can obtain gypsum via mining or quarrying, while phosphogypsum production is via phosphate production from phosphate rock. So, in terms of method of production, this is also a difference between gypsum and phosphogypsum.
Summary – Gypsum vs Phosphogypsum
Gypsum and phosphogypsum are hydrated forms of calcium sulfate. The key difference between gypsum and phosphogypsum is that gypsum is a naturally occurring form of calcium sulfate, whereas phosphogypsum is a synthetic form of calcium sulfate.
Reference:
1. “Phosphogypsum.” Wikipedia, Wikimedia Foundation, 7 Nov. 2019, Available here.
Image Courtesy:
1. “Gypsum (12249949575)” By James Petts from London, England – Gypsum (CC BY-SA 2.0) via Commons Wikimedia
2. “Kėdainių fosfogipso kalnai” By Hugo.arg – Own work (CC BY-SA 4.0) via Commons Wikimedia
[7:22 pm, 29/04/2022] Martin Fey: Even so the crystallinity is paramount. So much of the research done with phosphogypsum may give exaggerated prospects.
[8:43 pm, 29/04/2022] Rex Fey: Martin, What do u mean by crystallinity
[9:40 pm, 29/04/2022] Martin Fey: Gypsum is CaSO4 with two water mols and quite pure so even when finely powdered it consists of well ordered crystals that have a definite solubility in water. That’s the mineral gypsum that you find in nature and is mined.
The gypsum produced as a by product of the phosphate fertilizer industry contains impurities replacing some of the sulfate in the crystal structure, chiefly fluoride and phosphate ions. This destabilises the gypsum making it poorly crystalline and more readily dissolved in water. This is superior to the mined gypsum because it reacts faster.