The phosphorus industry produces over 1.5 million tons of white phosphorus annually from phosphate ores for uses such as matches. It also produces over 5 million tons of phosphoric acid with applications in fertilizer and other industries. Phosphate rocks commonly contain fluorapatite and are mined from large sedimentary deposits. White phosphorus is produced through high-temperature furnace reactions between phosphate rock, coke, and silica that produce phosphorus gas. The gas is condensed and handles carefully due to the reactive and hazardous nature of white phosphorus. Water and off-gases from production require treatment to remove phosphorus and fluorides before discharge or reuse.

1. PHOSPHORUS INDUSTRY

2. INTRODUCTION
• This industry shares a common root with the Fertilizer Industry.
• It uses less than 10% of the annual world production of phosphate ores.
• Both the phosphorus and the Fertilizer Industries are serviced by a
common primary phosphoric acid technology.
• The international phosphorus industry has a capacity of of producing over
1.5million tons of white elemental hazardous phosphorus used for making
matches world-wide from rich phosphate ores.
• It also makes a provision of more than five million tons if pure phosphoric
acid, for a variety of applications. The value of this acid is about three time
per tonne that of equivalent fertilizer acid.

3. OCCURRENCE OF PHOSPHATE ROCKS
• Since elemental phosphorus is very reactive, it occurs in combined form in
nature.
• Although phosphorus compounds of many kinds are essential for life in
plants and animals, it is majorly the metal phosphates that represent the
useful raw materials and mainly in the form of apatite.
• Apatite are generically A10(XO4)6Z2.
• Hard igneous phosphate rocks have a greater preponderance of
fluorapatite Ca10(PO4)6F2.
• More common sedimentary rocks are usually carbonate apatite often
occurring with structures of the Francolite type or even as fluorapatite
mixed with Dahllite Ca10(PO4)6-x (CO3)x(OH,F)2-×.

4. OCCURRENCE OF PHOSPHATE ROCKS
• The map in Figure 1 shows the broad world distribution, the most
commercially exploited regions USA, North Africa, and CIS having huge
sedimentary rock deposits which account for a substantial proportion
of the workable reserves of rock which can be readily up-graded to the
useable levels of more than 30% P2O5 (>13% P).
• Much phosphate is recovered by open-cast mining, but much larger
world resources 200-300 × 109 tons are available given a greater
capability for deep underground mining and extensive beneficiation.
• Commercial phosphate deposits vary in P2O5, in organic content and in
many secondary elements.

5. OCCURRENCE OF PHOSPHATE ROCKS
• Most rocks require beneficiation to remove other undesirable minerals and
clays.
• They are ground, washed, screened, deslimed, and magnetically separated.
• Floatation is used to separate apatite from silica, and calcination to reduce
carbonated and organics.
• Modern fertilizer acid technology calls for an optimum of iron, magnesium,
and aluminium, and low levels of organics and carbonates for good
processability.
• For industrial phosphoric acid, control of secondary elements means that
arsenic, cadmium, vanadium, or uranium may become part of rock
specifications together with P2O5, sizing, excess lime, moisture and so on.

6. WHITE ELEMENTAL PHOSPHORUS
• Production
• A prime constituent of the rock used to produce P4 is fluorapatite
Ca9(PO4)6CaF2 since rock is further intensively calcined.
• The chemistry of the furnace operation may be notionally expressed into a
primary reduction.
• 2Ca3(PO4)2 + 6SiO2 + 10C ------ 6CaSiO3 + 2P2 + 10C – 3MJ ----------1
The strongly exothermic reduction of tricalcium phosphate by carbon in the
presence of silica requires temperatures around 1200oC to proceed
vigorously but about 1400-1500oC to expedite with the simultaneous
removal of molten slag; only about half of the energy input is used in the
thermodynamics of the equation 1.

7. WHITE ELEMENTAL PHOSPHORUS
• Much of the CaF2 remains ‘unreacted’ in the furnace, the flag being
broadly a mixture of a silicate mineral wollastonite and flourine
containing mixed mineral cuspidene.
• About 25% of the fluorine is reacted, coming over the top via the
secondary reaction:
• 2CaF2 + 3SiO2 ---SiF4 + 2CaSiO3 ----------------------- 2
• Figure 2 shows a prototype furnace of the American TVA
development of some decades ago. State of the art technology of
phosphorus production is today optimized in furnace of electrical
loadings of 60-80MW.

9. WHITE ELEMENTAL PHOSPHORUS
• These are typically constructed as a tall cylindrical shell shell of
around 12m diameter, lined with refractory, and having a carbon
hearth, normally covered with molten slab in operation.
• Power is supplied by three large consumable carbon electrodes
vertically mounted passing, via special gas-tight telescopic seals,
through holes in the arched refractory roof.
• These electrodes can be renewed either by fitting new screw-in
sections, (Typically 1.4 × 2.75m, weighing 10 tons in North American
furnaces) or continuously by baking graphite paste, in the Soderberg
electrode construction of German furnaces and those used in massive
installations of Kazakhstan (different roof designs also being needed).

10. WHITE ELEMENTAL PHOSPHORUS
• The reaction profile of a phosphorus furnace is complex; the electrodes
provide power in some combination of resistive and arc heating, and are
sustained on hydraulic rams which permit (via control technology) the
electrical profile to be optimized.
• The furnace burden has to be sufficiently open to permit reasonable flow
and counter-current heat transfer of off-take gases.
• The sizing and preparation of coke, silica, and especially rock (which has to
be pelletized or modulized and calcined above 1000oC) is vital.
• Breakdown of reactor solids can result in sintering in the furnace with
irregular performance and with channelling and high gas velocities which
entrains solids that stabilize colloidal behaviour in the condensing system
producing ‘phosphorus mud‘ .

11. WHITE ELEMENTAL PHOSPHORUS
Gases leaving the furnace top at about 300oC consist P4, CO, CO2, H2,
and SiF4.
• These are passed through dust-removing stages and the P4 is largely
condensed by warm (70oC) water sprays, followed by a colder
finishing condenser (P4 melts 44.1oC).
• Phosphorus mud has to be removed in a settler before the pure P4
is pumped to store, and fluorosilicic in the aqueous streams has to
be neutralized.
The CO/H2 stream can be the source of fuel after cleaning.
• At the bottom of the furnace the reducing conditions are such that,

12. WHITE ELEMENTAL PHOSPHORUS
• Iron oxide (1-2%) in the rock goes to iron, which combines with some
phosphorus (Fe3P) and a little silicon (C/SiO2) to form a small heavy
molten phase on top of which sits the major burden of molten
calcium silicate slab (1400-1500oC).
• These molten phases are tapped ( the metal has some mettalurgical
value) and the 8-10 tons of slag per ton P4 have to be cooled and
broken for uses, or landfiled.

13. ENVIRONMENTAL ASPECTS OF WHITE
ELEMENTAL PHOSPHORUS PRODUCTION
• The preparation of rock feed (e.g. Pelletizing) can result in calcination
off-gases containing significant amounts of hydrogen fluoride which
has to be absorbed, neutralized, and either disposed to waste or
economically recovered.
• The substantial amounts of water used in condensing, settling, and
storing phosphorus (collectively known as ‘phossy water’) can contain
dissolved, and suspended P4, acids , and silica, etc.
• This water has to be neutralized with lime, forming precipitates, and
finally oxidized to remove any residual phosphorus before it can be
discharged.

14. ENVIRONMENTAL ASPECTS OF WHITE
ELEMENTAL PHOSPHORUS PRODUCTION
• Since most sources of phosphate rock contain minute quantities of
radioactive oxides which remain introduced in the furnace, the slag
will be a repository of these as complex ‘silicates’.
• Levels are no greater than those of some natural stones and may not
pose a problem depending upon geography and application.

15. HANDLING PHOSPHORUS
• White phosphorus is handled as a liquid for processing.
• It may be transported as solid under water in drums, in isotanks, or in rail
cars which are steam melted for use.
• Exposure to air gives rise to rapid oxidation with dense fumes, therefore in
pumping and plumbing that has to be taken into account.
• Transfers of liquid phosphorus within factories are normally effected using
a centrifugal pump whose body is immersed in water.
• Transfer lines are also heated and purged.
• Transfers to storage and to road or rail cars are effected by displacement
with water, phosphorus, and warm water circuits linked.

16. HANDLING PHOSPHORUS
• Water used in transferring phosphorus from tank cars to customers
may be returned to the phosphorus producer or handled under close
conservation.
• Careful control of blanket waters to pH < 8 to avoid formation of
gaseous phosphorus is done with buffers.
• Safeguards for employees include availability of emergency baths or
showers, heavy safety clothing, breathing apparatus, dental checks to
avoid necrosis, and antidotes for severe phosphorus burns.