Phosphate Recovery
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Some basics
Phosphorus and phosphates
Phosphorus is one
of the most common elements on earth and is essential to all living organisms.
In nature it always occurs combined with other elements, forming phosphates.
Phosphate resources
are located in the earths crust in the form of phosphate rock.
The main commercial
deposits are located in Morocco, the USA, the Former Soviet
Union, China and
South Africa. Western Europes only commercial deposit is
situated in Finland.
The known reserves
of currently exploitable phosphate rock are estimated at about
40 billion tons.
At the peak rate of consumption (150 million tons per year) these
reserves will last
more than 250 years.
In addition there
are bast phosphate resources present in the earth crust which, with
todays technology,
are not yet commercially exploitable.
Extending resources
Historically, the
main plant nutrients, nitrogen and phosphorus, were recycled in
agricultural communities.
Food was consumed close to its place of production and
the resulting animal
and human manures were applied to the same land.
The growth of cities
and the intensification of agriculture has led to the depletion of
soil nutrients.
Translocated away from the land, this resulted in the break-up of the
recycling loop.
Simultaneously the requirement for high crop yield has increased the
need for the application
of inorganic fertilisers.
One of todays challenges
consists of responding to the increasing demand for food
and the growing
nutrient requirement from agriculture without exhausting phosphate
mineral resources.
Main uses of phosphate
One of the keys to expanding the expected lifetime of these resources lies in restoring the nutrient recycling loop. In its simplest form, this would involve the transportation and application of sewage sludge from urban areas to agricultural land. New technologies are now becoming available to remove and recycle phosphate from wastewater, for use in both agricultural and industrial applications.
A multipurpose product
There are four main applications for phosphates.
Agriculture
Agriculture is by
far the largest user of phosphate, accounting for 80 to 85% of total
consumption. It
is one of the three main plant nutrients, along with nitrogen and
potassium, occurring
in inorganic fertilisers. In addition, an increasing number of
countries are using
phosphate contained in municipal wastewater sludge for
agricultural purposes.
Food and animal feed
supplements
Food grade phosphates
are used in many foods including dairy, meat, bakery
products and soft
drinks. Also, because of its high value as a nutrient, phosphate is
widely used in the
manufacturing of animal feed supplements. These applications are
discussed in the
Phosphate and Nutrition section.
Detergents
Until the middle
of this century, most domestic laundry was washed with soap-based
products. In 1947,
the first synthetic detergents for household use were introduced.
The appearance of
these new products on the market marked a major step forward in
the efficiency of
domestic laundry products, both in terms of hygiene and cleaning
performance.
At the heart of these
new formulations was sodium tripolyphosphate (STPP), used s a
"builder", a component
whose basic role is to soften water and to optimise the
washing conditions
for the other active ingredients. The qualities which make STPP
the builder of choice
are presented in the Phosphates and Laundry Detergents
section.
Other industrial applications
Apart from their role in laundry detergents, phosphates play a key role in dishwash detergent formulations and are also used in such diverse applications as metal surface treatment, corrosion inhibition, flame retardant, water treatment and ceramic production Despite such widespread use, these applications represent only about 3% of total consumption.
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