Granular Triple Superphosphate
Triple Superphosphate is a high analysis product
of the reaction between phosphate rock and phosphoric acid, containing
45 - 48% available phosphate (AP). Triple superphosphate plants
are mainly large units operating as a part of chemical complexes,
located near the source of phosphate rock. Therefore, a large
percentage of the world production is produced in Florida and
North Carolina, close to this major phosphate mining area.
While there are variations of processess used, the
two major routes are the so-called "solid" and "slurry
or quick-cure" processes with both routes together with
individual modifications being employed by the producers in Florida
and North Carolina. The properties of the triple superphosphate
depend upon the specific process used and on the granular or
non-granular nature of the product. The chemical and physical
characteristics of the material depend on the nature of the phosphate
rock, including composition(72-75 BPL) and degree of fineness
(70-85% minus 200 mesh), the concentration of the phosphoric
acid and the method of manufacturing.
Note: BPL = Bone Phosphate of Lime = 2.1852 x P2O5
In the production of run-of-pile or non-granular
triple superphosphate, phosphate rock and concentrated phosphoric
acid (50-54% P2O5) are brought together into a mixer which discharges
directly into a continuously moving den. A very dense slurry
is produced which solidifies readily into a porous, honeycomb-like
mass. It is carried to a rotating cutter where it is chopped
into particles and then conveyed to the storage area for pile
curing where the reaction continues for several weeks.
After curing, the material is reclaimed with power
equipment and shipped as run-of-pile triple superphosphate or
granulated by treatment with water and steam in a rotary drum,
followed by drying and screening and shipped as granular triple
superphosphate. Note: Granular Triple Superphosphate is the predomintate
product being produced today.
In the "slurry" granulation process, the
phosphate rock is reacted with relatively weak phosphoric acid
(32-40% P2O5). The resulting slurry is mixed with a large quantity
of dried, recycled fine granules which are coated with the slurry,
thus producing the desired granule size. The coated granules
are dried and screened and the product size material is withdrawn
to storage, the remainder being recycled to the process. The
product is ready for shipment without any further curing required.
Triple superphospate is shipped by rail and is exported
through the Florida and North Carolina ports for water shipment.
It is used in the formulation of high analysis grade fertilizers
and also applied directly to the soil as a single nutrient material.