Gas Treatment on Superphosphates Production

The production of phosphate-based fertilizers such as TSP (triplesuperphosphate) or SSP (simplesupephosphate), begins with a first step of attack of phosphate rock in the reactor, the obtained material passes through the Kuhlmann belt, where the reaction continues, ending in the granulator, and finally a drying step. In the four previous stages gas emissions are generated which have to be treated, being in the first two where the intensity and concentration is higher.

The contact of phosphate rock with an acid, normally H₂SO₄ or H₃PO₄ generates gaseous emissions. The gases produced are usually (F-) based, resulting from the presence of fluorures in the rock, that during the reaction, are released in the form of HF, SiF₄, F₂. Also a lot of dust and occasionally H₂S and CH₃SH are generated. These are the elements to be treated in a gas treatment system.

Two-phase solution

1. In a first phase F derivatives and dust are removed through venturi-cyclon systems in series, obtaining as by-products H₂SiF₆ and SiO₂ . This technology allows the recycling of H₂SiF₆ to the process of rock attack, so the liquid effluents to be treated are minimized. Within this process it is essential to control pH to avoid crystallization problems that could cause clogging of the equipment.
2. In case of presence of sulfur derivatives, a second phase is added in which these compounds are neutralized through a chemical scrubber with NaOH and oxidizing agents such as KMnO₄ or NaClO.

Principal advantages

• Environmental benefits: F- emissions below 5 mg/Nm3
• Economic benefits: process optimization that allows the generation of by-products that can be reused in the process itself and thus reduce the purchase of reagents.