Phosphate rock is an essential element for life on Earth. Discover its applications and why its mining threatens planetary health…
By Charlotte O’Gorman Lalor
Phosphate rock is any rock high in phosphorous content. Formed over millennia through igneous processes or via the accumulation of organic debris and phosphate-rich sediments, it is finite and irreplaceable. But why are its deposits – highly concentrated geographically from China, to the Middle East, northern Africa and the United States – so important?
Why is phosphate rock fundamental to life on Earth?
Phosphorous is vital for plant growth and photosynthesis; it promotes the absorption, storing and conversion of the sun’s energy into food. Phosphorous deficiency has great implications for soil fertility and crop yields – putting global food security in jeopardy amid rising population growth. Phosphate rock, in its pure, untreated form, is insoluble unless in acidic soils. This challenges plant uptake, however, when treated with sulphuric acid, it reacts to form phosphoric acid – a water-soluble material used to create a variety of synthetic fertiliser products.
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From this, we come to the dominant use of phosphate rock: as fertiliser. With 90 per cent of Earth’s mined phosphate rock utilised for agricultural fertiliser, totalling 49 million tonnes annually, it is key for ensuring productive and abundant crops. However, this raises questions about the overuse of phosphorus fertilisers.
Not only is phosphorous central to plant health, but to animal health and productivity. As the most abundant element in the animal body after calcium, it supports numerous physiological functions from animal growth to reproduction, gestation and lactation. Inadequate phosphorus levels can lead to deficiencies. This is why phosphate rock, in phosphoric acid form, is utilised for highly digestible animal feed and makes up 6 per cent of the market for world phosphoric acid production.
An interesting, emergent use of phosphate rock concerns are rare earth elements (REE). In Florida, significant sources of these minerals have been found in sedimentary phosphate deposits. Used in renewable technologies, such as solar and wind energy, as well as in everyday items including TVs and smartphones, these elements could enhance clean energy production. They are extracted more readily from phosphate rock which does not contain large amounts of hazardous radioactive elements, including uranium and thorium, common in many REE-rich deposits. It’s no wonder that phosphorous is found on the European Union’s list of minerals of importance to the economy.
How do we access this valuable resource?
Phosphate rock is mined during large-scale efforts. In strip mining, rock and soil above phosphate deposits are drilled, blasted, and removed via a large excavator. When the phosphorite is uncovered, it is extracted and transported using conveyor belts to nearby plants.
The original site must go through a process of reclamation – where mined land is reshaped to reinstate its original topography and reforested to replace the original habitat. Once completed, phosphate ore undergoes a process named ‘beneficiation’, which removes commercially worthless material, or impurities, including sand, quarts and clay.
What is the history of phosphate rock mining?
To trace the origins of phosphate mining we must go back in time to England, Suffolk, in 1847. This was when the first documented commercial phosphate rock mining occurred, sourced for fertiliser using pics and shovels. Following on from this, large-scale mining kickstarted in the US, South Carolina in 1868, before shifting locations due to the discovery of new, higher quality deposits. Since then, recent decades have witnessed phosphorite mining skyrocketing, led by the US, China and Morocco – with global production totalling 180 to 190 million tonnes annually.
However, the continual discovery of new phosphate deposits, including a 70 billion-tonne site in Norway, has extended global reserves and mining opportunities.
The dark side of phosphate rock
The use of phosphate rock is shrouded by environmental damage. Liberally applying phosphorus fertiliser causes substances to leech into rivers, streams and lakes. The over-enrichment of these water bodies stimulates the growth of plants and excessive algae blooms. This causes hypoxia, also known as oxygen depletion forming a ‘dead’ zone, transforming waters into festering swamps plagued by the loss of fish and aquatic life. In turn, this has led to the near-death of thousands of lakes globally, including Lake Erie located between the US-Canada border.
The process of accessing phosphate rock is equally damaging. From carbon emissions derived from the refining process to deforestation and habitat destruction, it leaves behind a trail of human destruction. The landscape is scarred by uneven hollows, unsuitable for habitation or agriculture.
Producing phosphoric acid also produces phosphogypsum, a by-product that contains elevated levels of uranium and its decay products including cancer-causing radon gas. This concentrate is far more radioactive than the original phosphate rock. This watery waste is stored in large, flat-topped, engineered piles named stacks, with wastewater ponds at the centre. While some are hundreds of feet high, these stacks are engineered to encourage evaporation and the formation of a crust. However, water from underneath and near these stacks can infiltrate and pollute local groundwater through sinkholes and breeches.
In a notable example, HRK Holdings, the owner of a phosphate mining plant named Piney Point near Tampa, Florida, discovered tears in the plastic liner of their waste-water-holding phosphogypsum stack in 2021. To alleviate this pressure and prevent a larger catastrophe, they released 35 million gallons of polluted wastewater into local waterways per day. This is a scenario we may see more often. As climate change increases the risk of extreme weather events and flooding, the question arises: how can evaporation keep up with rainfall in these phosphogypsum stacks? We may see the risk of pond collapse and flooding increase, which can send this toxic waste into the direction of homes and businesses, generating social and ecological disasters.
What does the future look like for phosphate mining?
Reports from scientists urge that global phosphate production will peak around 2030 – and thereafter, global reserves will be depleted. We may reach ‘peak’ phosphorous within the next 50 to 100 years. So what can be done? The answer: we must transform the way we use phosphorous.
One suggestion involves restoring natural habitats and biodiversity, which is key to restoring the phosphorous cycle and improving natural dispersal rates. Estimates suggest that by restoring seabird and fish populations, 4.8 billion dollars worth of phosphorus could be distributed around the world annually.
Another option involves the recycling and recovery of phosphate, otherwise known as circular economy principles. Imagine this: phosphate rock is mined from Asia, Africa, the Americas and Europe. From here, it is refined into fertiliser, and spread across arable land, generating a productive crop of soybeans that lands tofu on your dinner plate. Inevitably, your waste will be flushed down the loo, the phosphorous molecule worlds away from where it originated. These molecules can be recovered from our wastewater, sewage, manure, food waste and even from farmed soil, using biological and chemical methods. But why is this so important? Not only does it reduce our dependency on new phosphate rock mines, but it also fulfils our needs sustainably. Productive reuse does not outstrip phosphorite’s rate of regeneration.
With phosphorite being such a crucial resource – the building block to life on earth – one thing is certain: the time to act is now.
