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July 2012
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What is Rock Phosphate? What are uses of rock phosphate? How to manufacture it?

• Rock Phosphate organic fertilizer (RP) is a good source of Phosphorus, Calcium and other trace minerals.
• Rock Phosphate is a natural source of mined RP.
• Rock Phosphate will not leach out of the soil.
• Rock Phosphate will remain until taken up by the plant’s roots.
• Rock Phosphate organic fertilizer is insoluble in soils.
• It has a pH of above 7.
• It releases Phosphorus very slow and can last up to five years.
• It contains over 30% total Phosphorus with 3% available and 48% calcium.
• Rock phosphate is the raw material used in the manufacture of most commercial phosphate fertilizers on the market.
• Ground rock phosphate itself has been used as a source of P for acid soils.

Uses of Rock Phosphate

• Used as a long-lasting source of phosphorus.
• Used as bulb food and transplanting fertilizer.
• It has high phosphorus content.
• Used as good mix with creating customized organic fertilizers.
• Will not burn plants.
• Beneficial for flowering plants.
• Used in top layer of your garden soil as here new roots can find it.

Steps for manufacturing phosphate fertilizers

Various steps used in the manufacture of various phosphate fertilizers. Phosphoric acid is produced by either a dry or wet process.
1. Dry process
• In the dry process, rock phosphate is treated in an electric furnace.
• This treatment produces a very pure and more expensive phosphoric acid (frequently called white or furnace acid).
• It is used primarily in the food and chemical industry.
• Fertilizers that use white phosphoric acid as the P source are generally more expensive.
• This is because of the costly treatment process.

2. Wet Process
• The wet process involves treatment of the rock phosphate with acid producing phosphoric acid (also called green or black acid) and Gypsum.
• Gypsum is removed as a by-product.
• The impurities which give the acid its color have not been a problem.
• Either treatment process (wet or dry) produces orthophosphoric acid—the phosphate form that is taken up by plants.

About the Phosphoric acid

• The phosphoric acid produced by either the wet or the dry process is frequently heated.
• This is to drive off water and producing a superphosphoric acid.
• The phosphate concentration in superphosphoric acid usually varies from 72 to 76%.
• The P in this acid is present as both orthophosphate and polyphosphate.
• Polyphosphates consist of a series of orthophosphates that have been chemically joined together.
• Upon contact with soils, polyphosphates revert back to orthophosphates.
• Ammonia can be added to the super phosphoric acid to create liquid or dry materials.
• These materials contain both nitrogen (N) and P.
• The liquid, 10-34-0, is the most common product.
• The 10-34-0 can be mixed with finely ground potash (0-0-62), water, and urea-ammonium nitrate solution (28-0-0) to form 7-21-7 and related grades.
• The P in these products is present in both the orthophosphate and polyphosphate form.
• When ammonia is added to the phosphoric acid that has not been heated, monoammonium phosphate (11-52-0) or diammonium phosphate (18-46-0) is produced.
• This production depends on the ratio of the mixture.
• The P present in these two fertilizers is present in the orthophosphate form.
• The cost of converting rock phosphate to the individual phosphate fertilizers varies with the process used.
• The processes used have no effect on the availability of P to plants.

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