This paper compared 9 different phosphoric acid production processes and ranked them by their economic efficiency.

1. Phosphoric Acid Process Comparison
by Donal S. Tunks, Process Engineer, Jacobs Engineering S.A. (JESA)
donal.tunks@jacobs.com
Executive Summary
From a rigorous analysis of the capital and operating costs of 9 different processes to
produce phosphoric acid from phosphate rock, the different processes can be ranked by
their economic efficiencies. The rankings established in this analysis are as follows:
1. Dihydrate Process
2. Hemi-Dihydrate Process
3. Hemi-Dihydrate Recrystallization Process
4. Hemihydrate Process
5. Di-Hemihydrate Process
6. Nitrophosphate Process
7. Furnace Process
8. Thermal Process
9. Hydrochloric Acid Route
The Dihydrate Process surpassed recrystallization processes due to the high additional
cost of recrystallization processes. This extra investment is not compensated by the
increased P2O5 recovery and by the increased electrical production from lower steam
consumption. The Hemihydrate Process comes at a slightly lower investment cost than
the Dihydrate Process yet there is a significant drop in P2O5 recovery, so two
recrystallization processes surpassed it in economic efficiency. The Di-Hemihydrate
Process has the highest total investment cost of all processes with acidulation with
sulfuric acid which makes the Hemihydrate process more economical even with a
difference in P2O5 recovery of 6%. Implementing the Nitrophosphate Process requires a
huge investment which has a slightly lower payback than processes with sulfuric acid
acidulation. The Furnace Process does have a lower operating cost than the Dihydrate
Process yet not enough to justify an extra 123 million USD investment cost of a 500,000
tpy P2O5 Phosphoric Acid Plant. Due to the high cost of electricity, the Thermal Process
(Electric Arc Furnace Process) will not return a profit when used to make Phosphoric
Acid. The Hydrochloric Acid route showed to be more unprofitable than the Thermal
Process if Hydrochloric Acid was purchased so it received the lowest ranking.
Some of the assumptions made in this analysis includes that the phosphate rock used was
quality K09 from the Kingdom of Morocco, all sulfuric acid plants will have
cogeneration with HRS, and that an ammonia plant is required for the implementation of
the Nitrophosphate Process.
Introduction
Over the years, many different Phosphoric Acid Processes have been developed, some of
which have fallen out of use and others have not yet been fully developed. This paper

2. will present the underlying economics behind several different routes of phosphoric acid
production. The paper is based on generic processes for each of the routes rather than
processes offered by specific licensors.
The Phosphoric Acid Production Processes that will be analyzed are as follows:
• Dihydrate Process
• Hemihydrate Process
• Hemi-Dihydrate Process
• Di-Hemihydrate Process
• Hemi-Dihydrate Recrystallization Process
• Nitrophosphate Process
• Hydrochloric Acid Route
• Thermal Process
• Furnace Process
In the evaluation of these processes, the total cost to produce phosphoric acid will be
compared against the total installed cost of a facility. The processes will then be ranked
by determining the incremental rate of return between different facilities. To determine
the incremental rate of return, the increase in profit of a facility is divided by the increase
in cost of a facility. If the incremental rate of return is greater than the rate of return of
the facility it is being compared against, then this facility is considered to be more
economically efficient.
To determine the cost of the different facilities, various news articles and technical papers
were consulted and these costs were scaled up to a 500,000 tpy P2O5 (1500 tpd P2O5)
facility based on the 2010 USD. The total installed cost of the different facilities
presented in this paper does not have any relation to what would offered as a competitive
bid offered by Jacobs Engineering Group or by Jacobs Engineering S.A. (JESA).
In the analysis of the different wet processes with acidulation with sulfuric acid, sulfur
consumption was set at 1t/t P2O5 for the Dihydrate Process and the sulfur consumption
was increased or decreased based on the P2O5 recovery. This assumption was based on
the fact that citrate soluble losses (Cocrystallized Phosphoric Acid Losses) and water
soluble losses (Filtration Losses) would vary with P2O5 recovery and the citrate
insoluble losses (Unreacted Phosphate Rock Losses) will stay constant. The P2O5 that is
lost due to C.S. & W.S. losses first requires acidulation of phosphate rock into phosphoric
acid. Therefore a decrease in P2O5 recovery increases the consumption of sulfur.
The effect of gypsum quality and acid concentration on filtration rates was excluded from
the analysis. In general, the filtration rate for hemihydrate tends to be higher than for
dihydrate due to the irregularity of the hemihydrate crystals. Also, higher P2O5
concentrations increase the filtration rate because the viscosity of phosphoric acid
increases exponentially with concentration.

3. Basis of Comparison
The following Raw Material and Products Costs were used to estimate the operating
costs:
Raw Material / Product Cost
Calcium Ammonium Nitrate 250 USD/tonne
Hydrochloric Acid (33%) 160 USD/tonne
Phosphate Rock 130 USD/tonne
Sulfur 150 USD/tonne
Phosphoric Acid 800 USD/tonne
Natural Gas 18.4 USD/GJ
Petroleum Coke 50 USD/tonne
Calcium Carbonate 10 USD/tonne
Dihydrate for Building Material 35 USD/tonne
Hemihydrate for Plaster 50 USD/tonne
Sand 6 USD/tonne
Electricity (Purchase Price) 50 USD/MWh
Electricity (Selling Price) 25 USD/MWh
Dihydrate
The Dihydrate Process involves the acidulation of Phosphate Rock with Sulfuric Acid
which results in the production of Phosphoric Acid and the precipitation of Calcium
Sulfate Dihydrate. Following acidulation, the Dihydrate is filtered from the reactor slurry
and the phosphoric acid is sent to storage. In the evaluation of this process it will be
assumed that phosphoric acid at a concentration of 28% P2O5 will be produced with an
overall recovery of 95%.
The Dihydrate Plant considered in his comparison consists of a Sulfuric Acid Plant with
cogeneration & HRS, Phosphate Rock Grinding, Reaction/Filtration, Filter Acid
Clarification & Storage, Phosphoric Acid Concentration, and Merchant Grade Acid
Clarification & Storage.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the Dihydrate
Process was estimated to be 240 million USD.
The annual profit for the Dihydrate Process was determined by tabulating the revenue
from phosphoric acid and electrical sale and subtracting the cost of phosphate rock,
sulfur, general operating costs, and gypsum disposal. General operating costs include
operating labor, maintenance labor, reagents, plant overhead, maintenance, operating
supplies, insurance, taxes, and depreciation. General operating costs was assumed to be
40USD/t P2O5. With the exception of the Di-Hemihydrate process, all wet processes
with acidulation with sulfuric acid will include a gypsum stack. The cost of a gypsum
stack was spread out over the operating lifetime of the plant. With all that said, the

4. annual profit of a phosphoric acid plant by the Dihydrate Process was determined to be
88 million USD.
Hemihydrate
The Hemihydrate Process involves the precipitation of Calcium Sulfate Hemihydrate and
this process can produce phosphoric acid at a significantly higher concentration than the
Dihydrate Process. To promote the formation of Hemihydrate, the reactor must maintain
a higher temperature and a higher %P2O5 than the Dihydrate process. The Hemihydrate
process experiences significantly higher lattice losses and the overall P2O5 recovery is
typically around 92%.
The cost of a Hemihydrates Plant will differ from a Dihydrate Plant due to the following:
• Less Phosphate Rock Grinding is required
Since a Hemihydrate Reactor operates at a higher temperature and a higher
%P2O5, a larger particle size can digested. This is further accomplished through
the use of a low sulfate section followed by a high sulfate section in the reactor.
• Number and size of Reactor Flash Coolers plus auxiliary equipment is different
Two Reactor Flash Coolers are required in the Hemihydrate Process. Although
the Reactor Flash Coolers are smaller in size, the cost of both greatly outweighs
the single Flash Cooler required for the Dihydrate Process.
• Reduced Size of Filter Acid Clarification & Storage
Since phosphoric acid is at a higher concentration (40% P2O5) than the Dihydrate
Process, the volume of filter acid that needs to be clarified and stored is
significantly less.
• Reduced Size of Phosphoric Acid Evaporation
Evaporating phosphoric acid from 40% P2O5 to 54% P2O5 can be done with
46% less evaporator capacity than with the Dihydrate Process.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the
Hemihydrate Process was estimated to be 224 million USD.
The calculation of the annual profit for the Hemihydrate Process uses the same method
described for the Dihydrate Process. The annual profit of a phosphoric acid plant by the
Hemihydrate Process was determined to be 80 million USD.

5. Hemi-Dihydrate
This process is a two stage filtration process where Hemihydrate is crystallized and
filtered in the first stage and recrystallized to Dihydrate and filtered in the second stage.
The Acid produced in the Hemihydrate stage is sent to storage, and the liquor from the
recrystallization section is used on the Hemihydrate filter. The Hemi-Dihydrate process
produces a high strength phosphoric acid similar Hemihydrate process and overcomes the
high lattice losses experienced in the Hemihydrate process by recrystallizing the
Hemihydrate into Dihydrate. The P2O5 recovery for this process is 98%.
The differences between a Hemihydrate Plant and a Dihydrate Plant applies to a Hemi-
Dihydrate Plant as well. The following differences are also included in evaluating a cost
of a Hemi-Dihydrate Plant to a Dihydrate Plant:
• Recrystallization Tank is required
The Recrystallization Tank is what transforms the Hemihydrate crystals into
Dihydrate. The retention time of the Recrytallization Tank was assumed to be
one hour at 40% solids.
• Second Filter Building is required
The addition of a second filter building is extremely expensive and this fact is
what brings into question the economic efficiency of two stage processes.
• Larger Fume Scrubber
The increased filtration area, as well as the recrystallization tank require aeration.
This increases the amount of air that needs to be scrubbed which increases the
size of the fume scrubber.
• Larger Overall Installed Capacity
Due to discontinuities between filter washes of the first and second stages. A 5%
extra overall capacity is required to produce the design capacity.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the Hemi-
Dihydrate Process was estimated to be 271 million USD.
The calculation of the annual profit for the Hemi-Dihydrate Process uses the same
method described for the Dihydrate Process. The annual profit of a phosphoric acid plant
by the Hemi-Dihydrate Process was determined to be 99 million USD.

6. Di-Hemihydrate
The Di-Hemihydrate Process can be characterized as a Hemi-Dihydrate Process in
reverse. The acidulation section consists of crystallization of Dihydrate, Dihydrate
filtration, Hemihydrate Recrystallization, then Hemihydrate filtration. The claimed
advantage of this process is that the recrystallized Hemihydrate can be used as a building
material without any drying because all the residual moisture is absorbed when the
Hemihydrate recrystallizes again into Dihydrate.
Like the Hemi-Dihydrate Process, the Di-Hemihydrate Process requires a
Recrystallization Tank, a Second Filter Building, Larger Fume Scrubber, and Larger
Overall Installed Capacity. For a description of these units, please refer to the previous
section regarding the Hemi-Dihydrate Process.
The Di-Hemihydrate, Hemi-Dihydrate, and Hemi-Dihydrate Recrystallization Processes
all produce relatively pure gypsum which can be sold as a construction material in most
countries. For the Hemi-Dihydrate and Hemi-Dihydrate Recrystallization Processes,
gypsum sale will not be considered because the profit loss to dry and sell the gypsum will
be greater than the cost of stacking gypsum. For the Di-Hemihydrate Process,
Hemihydrate sale will be considered.
The recrystallized Hemihydrate from the second stage will have a residual moisture of
35%, if K09 phosphate is used. Of this 35% residual moisture, only 12% can be
absorbed leaving a 23% residual moisture. This 23% residual moisture makes drying the
resulting Dihydrate for sale unprofitable. Even though more water needs to be
evaporated to produce Hemihydrate, Hemihydrate can be sold at a higher price. Due to
the high fuel consumption of drying gypsum, a very small profit is returned for
Hemihydrate sale. A gypsum post-processing unit for Hemihydrate sale has been
estimated to be 35 million USD.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the Di-
Hemihydrate Process was estimated to be 287 million USD without Gypsum post-
processing and 322 million USD with Gypsum post-processing.
The calculation of the annual profit for the Di-Hemihydrate Process uses the same
method described for the Dihydrate Process except that gypsum stacking was replaced by
Hemihydrate sale. The cost of fuel and electrical consumption from the Gypsum post-
processing unit was also included. The annual profit of a phosphoric acid plant by the
Di-Hemihydrate Process was determined to be 108 million USD.
Hemi-Dihyrate Recystallization
Hemi-Dihyrate Recystallization is a single filtration phosphoric acid process where
Hemihydrate is initially formed in a high temperature reaction with sulfuric acid. The
Reactor Slurry is subsequently cooled in a set of crystallizers to recrystallize the
Hemihydrate into Dihydrate. Due to the recrystallization from Hemihydrate into

7. Dihydrate, the majority of the lattice losses from the initial Hemihydrate step are
recovered. The process produces phosphoric acid with a concentration of 32% P2O5 and
the theoretical P2O5 recovery is 98%.
This process requires an enormous reaction section which significantly increases the cost
of the facility. The reaction section for this process is relatively small and the remainder
of the reactor consists of the recrystallzation section. A large recrystallization volume is
required for this process due to the fact that the recrystallization of Hemihydrate in
Dihydrate happens slowly at higher %P2O5 concentrations. Other additional costs are
due to additional equipment to cool the slurry in the Recrystallizers and a larger scrubber
to handle the increased aeration of the reactor. Credit is also given for the smaller Filter
Acid Clarification & Storage volume and the smaller Phosphoric Acid Evaporators.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the Hemi-
Dihydrate Recrystallization Process was estimated to be 270 million USD.
The calculation of the annual profit for the Hemi-Dihydrate Recrystallization Process
uses the same method described for the Dihydrate Process. The annual profit of a
phosphoric acid plant by the Hemi-Dihydrate Recrystallization Process was determined
to be 97 million USD.
Nitrophosphate Process
The definition of a Nitrophosphate Process is a process that involves acidulation of
Phosphate Rock in Nitric Acid. The Nitrophosphate Process that will be considered is as
follows:
Phosphate Rock is attacked with Nitric Acid the resulting mixture stays in solution.
Calcium Nitrate Tetrahydrate (CNTH) is then crystallized at a temperature ranging from
0-20°C, which is then filtered and the phosphoric acid is sent to storage. The CNTH is
dissolved then reacted with CO2 to remove a portion of the calcium and the resulting
Calcium Carbonate is separated. The solution is then ammoniated and granulated to
produce calcium ammonium nitrate (CAN). All other Nitrophosphate processes that have
been physically or conceptually devised are beyond the scope of this paper.
It was assumed that if a nitrophosphate process was to be implemented for the production
of phosphoric acid, the construction of an ammonia plant, nitric acid plant, nitrophoshate
plant, and CAN granulation plant would be required. Due to the high volumes of
ammonia required to produce nitric acid, it would not be practical to purchase ammonia
therefore an ammonia plant was included with the cost of a nitrophosphate complex.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the
Nitrophosphate Process was estimated to be 1.1 billion USD.
The total annual cost of Natural Gas, phosphate rock, electricity, general operating costs
and catalyst for the nitric acid plant was compared against the sale of phosphoric acid and

8. CAN. The General Operating Costs were assumed to be 60 USD/t P2O5 for the entire
complex which includes an ammonia plant, nitric acid plant, nitrophoshate plant, and
CAN granulation plant. From this, the annual profit was determined to be 369 million
USD.
Hydrochloric Acid Route
Phosphoric Acid can also be produced by reacting phosphate rock with hydrochloric acid.
Since the Calcium Chloride cannot be precipitated at a reasonable temperature range, the
phosphoric acid is removed from solution via solvent extraction. This process can
produce super phosphoric acid and with less waste than a process that uses sulfuric acid.
A limitation to this process is that it can only be implemented near the sea for disposal of
Calcium Chloride into the ocean. Therefore, the environmental impact of the HCl route
is much greater than a process with gypsum stacking.
The total cost of phosphate rock, hydrochloric acid, electricity, plus 40 USD per tonne of
P2O5 of general operating cost was compared the sale price of 800 USD/tonne P2O5. It
was determined that the production of phosphoric acid using hydrochloric acid could not
return a profit in today’s market.
The cost of a Plant to produce 500,000 t P2O5/year of phosphoric acid from acidulation
with hydrochloric acid was determined to be 300 million USD.
Thermal Process
The Thermal Process (Electric Arc Furnace Process) was the primary mention of
producing phosphoric acid before being dominated by the wet process with sulfuric acid.
In the Thermal Process, phosphate rock, silica, and coke are fed to the furnace and an
electric current is applied. The calcium in the phosphate rock fuses with the silica while
the carbon in the coke combines with the oxygen in the phosphate which allows P4 to
evaporate, and the P4 is condensed once leaving the electric arc furnace. In the
production of phosphoric acid, P4 is then burned forming P4O10 which is then scrubbed
with water to make phosphoric acid.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the Thermal
Process was estimated to be 379 million USD.
The thermal process consumes about 13,000 kWh/t P2O5 and general operating costs
were assumed to be 40 USD/t P2O5. The P2O5 recovery for the Thermal process was
assumed to be 92%. Applying these factors, it was determined that the Thermal Process
cannot return a profit for the production of phosphoric acid.
Furnace Process
The furnace process is similar to the Thermal Process, but the heat required to evaporate
P4 comes from the burning of petroleum coke instead of from electricity. Upon the

9. evaporation of P4, the P4 reacts with the oxygen in the furnace to form P4O10. The gas
laden with P4O10 is scrubbed with water to form phosphoric acid. The P2O5 recovery of
the furnace process is 87%.
The total cost of a phosphoric acid plant to produce 500,000 tpy P2O5 by the Furnace
Process was estimated to be 363 million USD.
In the evaluation of the annual profit of the Furnace Process, the total cost of phosphate
rock, coke, silica, electricity, and general operating costs were compared against the sale
of phosphoric acid. The annual profit was determined to be 103 million USD.
Comparison
The total cost of each facility along with the expected profit in today’s market and the
rate of return can be seen in the table below.
Process Cost Annual Profit Rate of
(Million USD) (Million USD) Return
Dihydrate 240 88 36.5%
Hemihydrate 224 80 35.7%
Hemi-Dihydrate 271 99 36.3%
Di-Hemihydrate 322 108 33.6%
Hemi-Dihydrate Recrystallization 270 97 36.0%
Nitrophosphate 1100 369 33.5%
Hydrochloric Acid Route 300 -396 -132%
Thermal 379 -172 -45.4%
Furnace 363 103 28.5%
Even though the rate of return on investment for a phosphoric acid production facility
seems high, these numbers only consider the profit gained for the market conditions as of
early 2011 and the time taken to construct a facility was not taken into account. The
construction time for the sulfuric acid based processes will be about the same since these
facilities are very similar. The Nitrophosphate Process will have a higher construction
time since it is a much larger facility.
Some selected incremental rates of return are as follows:
Base Process Upgraded to Incremental Upgrade
Rate of Return Economically
Efficient?
Hemihydrate Dihydrate 49.0% Yes
Dihydrate Hemi-Dihydrate 35.1% No
Dihydrate Di-Hemihydrate 25.2% No
Dihydrate Hemi-Dihydrate 31.9% No
Recrystallization
Dihydrate Furnace 12.9% No
Dihydrate Nitrophosphate 32.7% No

10. By calculating the incremental rate of return between all the different facilities, the
ranking of the different plants by economic efficiencies developed. The result of this
calculation gave the following result:
1. Dihydrate Process
2. Hemi-Dihydrate Process
3. Hemi-Dihydrate Recrystallization Process
4. Hemihydrate Process
5. Di-Hemihydrate Process
6. Nitrophosphate Process
7. Furnace Process
8. Thermal Process
9. Hydrochloric Acid Route
Even at the high cost of phosphate rock and sulfur, the Dihydrate Process still proves to
be the most economically efficient process.