What must phosphate rock be treated with before it can be utilized as a fertilizer?

Phosphate rock must be treated with acid before it can be utilized as a fertilizer because the treatment process transforms the rock into a more soluble form of phosphate that plants can readily absorb. The reaction between phosphate rock and acid generates phosphoric acid and other soluble phosphate compounds. These soluble forms are essential for plant growth, as they enable the phosphorus to be available in a form that roots can take up.

In contrast, simply adding water does not facilitate the chemical transformation necessary for phosphate rocks, as they remain inert in their natural state. While chalk is often used in agricultural practices for soil amendment or pH balancing, it does not serve the purpose of converting phosphate rock into a usable form. Similarly, ammonium solution is not a treatment for phosphate rock and does not lead to the necessary solubility required for effective fertilization. Thus, acid treatment is a critical step in processing phosphate rock into a functional fertilizer.