Production of HF from H2SiF6

Abstract

During the reaction of phosphate ore and sulphuric acid, silicon tetrafluoride (SiF4) and HF are formed as byproducts. These gases are usually scrubbed with water, forming fluorosilicic acid, H2SiF6 (FSA) as a waste stream. Until recent years, FSA was mostly used for drinking water fluorination and for the production of Aluminium Fluoride (AlF3) or, in most cases, was neutralised or disposed to sea or ponds. Research and pilot work for the industrialization of a process to produce hydrofluoric acid (HF) and anhydrous hydrofluoric acid (AHF) from FSA has been conducted for nearly six decades without having developed a process that was found suitable to be built on industrial scale. Buss ChemTech has scaled the process from pilot scale (800 t/a) in one step to full scale industrial plant. Since 2008, three plants with capacities of 12,000 and 20,000 tons (two plants) of AHF per year were erected and are in operation.