Question

Rhenania phosphate - a P containing fertilizer contains:

• A. 26-27% P$_2$O$_5$
• B. 28-30% P$_2$O$_5$
• C. 31-33% P$_2$O$_5$
• D. 34-36% P$_2$O$_5$

Hint:

Rhenania phosphate is a citric-acid soluble phosphorus fertilizer containing \(26\text{--}27\%\) \(P_2O_5\).
Citric-acid soluble fertilizers are highly suited for acidic soils, as they release phosphorus slowly and are less prone to fixation compared to water-soluble fertilizers.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Phosphorus fertilizers are categorized based on their solubility into water-soluble, citric acid-soluble, and insoluble types.
Rhenania phosphate is a thermal phosphate fertilizer produced by sintering rock phosphate with soda ash and silica at high temperatures.

Step 2: Detailed Explanation:
Let us analyze the chemical composition and manufacturing of Rhenania phosphate:
- It is manufactured by heating a mixture of ground rock phosphate, sodium carbonate (\(Na_2CO_3\)), and silica (\(SiO_2\)) in a rotary kiln at temperatures of approximately \(1100^{\circ}\text{C}\) to \(1200^{\circ}\text{C}\).
- This thermal treatment breaks down the insoluble apatite structure of raw rock phosphate, converting it into a citric acid-soluble calcium-sodium phosphate complex.
- This chemical form is highly available to plant roots in acidic and neutral soils, while preventing rapid phosphorus fixation in the soil.
- The finished Rhenania phosphate fertilizer typically contains a total phosphorus content of \(26\%\text{ to }27\%\text{ of }P_2O_5\), nearly all of which is soluble in a \(2\%\) citric acid solution.
Therefore, Option (A) is the correct range.

Step 2: Final Answer:
Rhenania phosphate contains 26-27% P$_2$O$_5$.