The ecophos process: Highest quality market products out of low-grade phosphate rock and sewage sludge ash

Abstract

Ecophos s.a. has developed a unique modular process for the valorization of low-grade phosphate rock and/or various alternative P resources such as sewage sludge ash on the basis of soft digestion by hydrochloric acid or phosphoric acid. The process is extremely flexible and is, by the modular setup, capable of using several types of raw materials and producing a variety of products (fertilizer-, feed-, and food-grade phosphoric acid (PA), animal feed (DCP and MCP), and liquid NPK, PK, and NP fertilizers). The process has economic and ecological advantages over conventional industrial processes and those in development for valorization of sewage sludge ash, since it is simple, stable, and easy to control without needing expensive chemicals, raw materials, and equipment. The performance has already been tested in industrial plants at Bulgaria, Syria, and Peru as well as pilot- and lab-scale installations. Uptime longer than 7800 h/a is easily reached and the yield on P 2 O 5 is 90% or higher. Furthermore the process can use excess HCl in the manufacture of products such as isocyanate, caustic soda, or SOP (Sulfate of Potassium). The energy balance is more positive than competing processes, since PA of high concentration ( > 42%) can be obtained without evaporation. The process can generate uranium (U)-free fertilizers, while conventional fertilizers generally contain 300-500 mg U/kg P 2 O 5 . Main by-products include high-purity CaCl 2 (as solution, flakes, or prills), radiation-free gypsum, silicate filter residue, and Fe/Al-chlorides. By applying different modules, most of the by-products can be split into sellable products, thereby minimizing final waste.