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What is Rock Phosphate? What is the chemical composition of rock phosphate?




• 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.

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.

Phosphate Fertilizer Terminology

1. WATER-SOLUBLE
• Fertilizer samples analyzed by a control laboratory are first placed in water .
• The percentage of the total phosphate that dissolves is measured.
• This percentage is referred to as water-soluble phosphate.

2. CITRATE-SOLUBLE
• The fertilizer material that is not dissolved in water is then placed in an ammonium citrate solution.
• The amount of P dissolved in this solution is measured.
• This is expressed as a percentage of the total in the fertilizer material.
• Phosphate measured with this analytical procedure is referred to as citrate-soluble.

3. AVAILABLE PART
• The sum of the water-soluble and citrate-soluble phosphates is considered to be the percentage.
• This percentage is available to plants and is the amount guaranteed on the fertilizer label.
• The citrate- soluble component is less than the water-soluble component.

Chemical composition of Rock Phosphate

• Rock Phosphate’ is a sedimentary rock composed of phosphate minerals high enough, most particularly in apatite.
• It is used directly in fertilizer and as a source of phosphorous compounds.
• Apatite includes 10 mineral species and has the general formula X5Y(PO4)3, where X is usually Ca2+ or Pb3+ and Y is F-, Cl-, or OH-.

– TOTAL PHOSPHATE
32.0 – 35.0%
– CALCIUM OXIDE
48.0 – 52.0%
– MOISTURE
1.5% max
– SILICA
2.5 – 5.0%
– FLUORIDE
4.0% max
– SULFATE
0.7 – 1.9%
– IRON
1.0% max
– ALUMINIUM
2.0% max
– SOLUBLE CHLORODE
0.05% max
– POTASSIUM OXIDE
0.3% max
– MAGNESIUM OXIDE
0.5% max
– PARTICLE SIZE
2.0% max (+4 mesh) + 65% ~ 80% min (-4 ~ +100mesh) + 15% ~ 25% (-100 ~ +200mesh) + 1% ~ 3% (-200 ~ +270mesh) + 1% ~ 3% (-270mesh)





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