Gypsum is a mineral that occurs in nature and as a by-product of many industrial processes. Gypsum is commonly used in industrial and agricultural applications worldwide.
Phosphogypsum refers specifically to the gypsum formed as a by-product of processing phosphate ore into fertilizer with sulfuric acid. As with almost all sources of gypsum, phosphogypsum contains impurities. Phosphogypsum may contain low residual concentrations of radium from the source rock (and other metals) and hence can potentially have a level of radioactivity associated with radon gas.
There is inconsistent regulation regarding phosphogypsum on a global level. Typically phosphogypsum is stacked in above ground storage facilities termed gypstacks. In 2013, the International Atomic Energy Agency (IAEA) released a study that provides a framework for safe and sustainable use of phosphogypsum based on current health and science information. The IAEA study utilizes a risk based criteria for use.
Where utilized, phosphogypsum is most commonly used as raw material, fertilizer, soil conditioner, road building, landfill cover, glass/ceramic, and housing. Excellent examples of sustainable reuse are present in Brazil, India, China, and Tunisia.It has also shown to improve the condition of saline soils and, as such, has already been used successfully used for land reclamation (near Huelva, Spain). Various countries have started exploring it as co-product to cement for road construction: Pilot roads have been successfully built in Finland, Africa and the U.S.
Source of sulphur
An important aspect regarding phosphogypsum is its potential to solve sulphur deficiency in soils. While elemental sulphur and organic sulphur must undergo microbial conversion before sulphur is made available to plant, the sulphur in phosphogypsum becomes readily available for being present in sulphate form.
In many regions worldwide, including North Africa, China, Australia, Brazil, India, Pakistan and Spain public -private partnerships are being developed to re-use it. Spain, for example, is re-using phosphogypsum as sulphur fertilizers in agriculture: It has been shown to significantly increase the yields of a wide range of crops, also by improving acidic subsoils.
Matching source and end use
The residual radium and metal concentrations of phosphogypsum depends on the source of rock used and the processing conditions. Consequently, risk management principles must be taken to match a given source of phosphogypsum to the appropriate end use. IFA promotes uniformization of regulations regarding the handling, storage and use of this by-product so that its potential may be used effectively, while its associated risks are minimized.