Waste from fertilizer production mosaic
These images show phosphogypsum waste from the production of fertilisers.
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FERTILISER
Modern agriculture is dependent on the use of fertilisers.
By fortifying the soil with essential nutrients – like nitrogen, potassium, and phosphorous – fertilisers can ensure the healthy growth of crops.
Traditionally, farmers have used manure on their fields to fertilise crops. However, it is also possible to make synthetic fertilisers using raw materials like minerals and industrial chemicals.
Phosphate fertilisers are synthetic fertilisers made from phosphate rock.
They provide plants with phosphorous, an essential nutrient for photosynthesis, plant metabolism, and plant growth.
Photo by Dietmar Reichle on Unsplash
Photo by Lucas Marconnet on Unsplash
In the UK, an average of 30.7kg of phosphate fertiliser is applied to each hectare of farmland.
In China, the use of phosphate fertiliser is even greater, with over 90kg of phosphate fertiliser applied per hectare of cropland each year.
PHOSPHATE ROCK
Phosphate rocks are sedimentary rocks containing high levels of the element phosphorous.
The phosphorous found in phosphate rocks often derives from the remains of ancient marine organisms, especially from tissues like shells or bones.
Although most sedimentary rocks contain a small proportion of phosphorous (typically 0.2%), phosphate rock contains at least 15% phosphorous.
Phosphate rock is heavily mined in China, the USA, and the Western Sahara.
Approximately 90% of phosphate rock that is extracted each year is used to support agriculture — either turned into supplements for animal feed or used to make phosphate fertilisers.
PHOSPHOGYPSUM
In order to make fertilisers, phosphate rock must first be processed to produce phosphoric acid. One of the waste products resulting from this reaction is phosphogypsum.
Phosphogypsum is a solid form of gypsum containing phosphorous and other trace elements.
For each tonne of phosphoric acid that is produced form phosphate rock, over 5 tonnes of phosphogypsum are released.
Usually, phosphogypsum is stored in solid stacks, like this one in Louisiana.
Although these stacks are built too far from houses for their radioactivity to pose a threat to human health, they are associated with other environmental concerns.
In Calgary, Canada, phosphogypsum stacks were found to release fluoride gas at up to 130 times the same limit.
If fluoride pollutes drinking water, it can contribute to bone disease, kidney disease, and other health problems.
Phosphogypsum contains trace amounts of uranium, making it weakly radioactive.
The uranium content of phosphogypsum does vary, however, depending on which source of phosphate rock it was derived from.
In 2020, the US government made the controversial decision to allow phosphogypsum with low radioactivity to be used for road construction.
However, phosphogypsum is often too dangerous to be repurposed, and so must be stored indefinitely as a hazardous waste product.
Photo by Kilian Karger on Unsplash
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