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If you are active in the metal industry or other chemical sectors, you might have a waste stream of sulfuric or hydrochloric acid.
Due to its low concentration or high amount of impurity, you cannot use it and must dispose of it but Prayon can recover it! Note that in some cases, spent acid may also refer to diluted phosphoric acid.
The GetMoreP process and Ecophos process are designed to work under diluted conditions. Respectively diluted Sulfuric Acid stream (GetMoreP) and diluted Hydrochloric Acid stream (Ecophos) are perfect to digest the phosphate rock through this process. Additionally, most of the metal impurities from respectively the spent sulfuric and hydrochloric acid will be removed through the digestion stage without affecting the quality of the DCP product.
In certain cases, diluted Phosphoric Acid can be recovered and reused in some applications including the upgrading of raw materials.
In Module 2A where the phosphate rock is selectively digested in the spent diluted sulfuric acid (H2SO4).
On one side, it leads to the formation of gypsum containing most of the impurities from the rock and the spent acid (sand, iron, aluminum, heavy metals…).
On the other side, the phosphate solution is recovered by vacuum filtration. In the following Module 2B, the phosphate solution is neutralised with limestone, quicklime, or slacked lime to crystallise the phosphate as dicalcium phosphate – DCP.
The first module is Module 1A where the low-grade phosphate rock is selectively digested in the spent diluted hydrochloric acid (HCl). This reaction produces a slurry of undigested phosphate rock as a solid with phosphate and calcium chloride (CaCl2) in solution.
In Module 1B, the phosphate solution is treated with CaCO3 to obtain dicalcium phosphate dihydrate (CaHPO4.2H2O, DCP) crystals and CaCl2 in the liquid phase.
In Module CCP, the CaCl2 solution is purified. In Module 4 (optional), CaCl2 is converted back to HCl by reaction with sulfuric acid after filtration, the HCl is returned to the rock digestion module, with a co-product of very pure and white gypsum.