SUPERPHOSPHATE

The Uses of SUPERPHOSPHATE

Fertilizer.

Definition

The most important phosphorus fertilizer, made by the action of sulfuric acid on insoluble phosphate rock (essentially calcium phosphate, tribasic) to form a mixture of gypsum and calcium phosphate, monobasic. A typical composition is CaH4(PO4)2?H2O 30%, CaHPO4 10%, CaSO4 45%, iron oxide, alumina, silica 10%, water 5%. Typical analysis: Moisture 10–15%, available phosphoric acid (as P2O5) 18– 21%, insoluble phosphoric acid 0.3–2%, total phosphoric acid (as P2O5) 19–23%.

Definition

A mixture – mainly calcium hydrogen phosphate and calcium sulfate – used as a fertilizer. It is made from calcium phosphate and sulfuric acid.

Definition

superphosphate: A commercial phosphate mixture consisting mainly of monocalcium phosphate. Singlesuperphosphate is made by treating phosphate rock with sulphuric acid; the product contains 16–20% ‘available’ P₂O₅:
Ca₁₀(PO₄)6F₂ + 7H₂SO₄ = 3Ca(H₂PO₄)₂ + 7CaSO₄ + 2HF
Triple-superphosphate is made by using phosphoric(V) acid in place of sulphuric acid; the product contains 45–50% ‘available’ P₂O₅:
Ca₁₀(PO₄)6F₂ + 14H₃PO₄ = 10Ca(H₂PO₄)2 + 2HF

Agricultural Uses

Superphosphate is obtained by treating phosphate rock with sulphuric acid, phosphoric acid, or their mixture. Rock phosphate mixed (a) with sulphuric acid (H₂SO₄) gives single superphosphate (9% phosphorus), and (b) with phosphoric acid gives triple superphosphate (20 to 22 % phosphorus).
Equal weights of finely ground rock phosphate and sulphuric acid are mixed in cast iron pans, equipped with a stirring mechanism. The fluid mixture is dropped into a 'hot den' where it solidifies. 15 to 30 minutes later, it can be used for making different grades of superphosphates. The main reaction between sulphuric acid and rock phosphate is as follows:
A guaranteed percentage of the available phosphoric acid determines the type of superphosphate produced; for instance, '20% superphosphate' or '45 to 50% superphosphate', which are single superphosphate (SSP) and triple superphosphate (TSP), respectively. The percentages indicate the amount of available phosphorus (as P₂O_{5/sub>).
Boronated single superphosphate is a modified form of single superphosphate. It contains 0.18% borax and is mostly available in western countries as a fertilizer.
Superphosphates are neutral fertilizers in that they have no appreciable effect on soil pH. Superphosphate (also called ordinary or single superphosphate) contains about 8 to 10% sulphur as calcium sulphate. Superphosphate is also used in the production of mixed fertilizers in which other dry, powdered or finelygranular materials are blended to effect a product that contains nitrogen, phosphorus and potassium. It is also applied directly. Ammoniated superphosphates are prepared by reacting anhydrous or aqua ammonia with ordinary or triple superphosphate. Ammoniation of superphosphates offers the advantage of inexpensive nitrogen but decreases the amount of water-soluble phosphorus in the product. The water solubility is greater in superphosphate than in triple superphosphate.}