Manufacturing Of Aluminium Fluoride in Phosphoric Acid Industries

Aluminium fluoride monohydrate AlF3H2O obtained as fluellite mineral, it is the natural form of aluminium fluoride available in earth crust. This material used for producing aluminium also. Some properties if aluminium fluoride, Its formula AlF3 with Specific  gravity 2.882.Heat of formation 331.5 kcal/gmol and melting point 1040  oC. Solubility in water 0.559 g/100 ml at 25 oC and the sublimation temperature is 1260 oC.

Some of the technical methods for manufacturing of aluminium fluoride

  1. From fluorspar: With the help of wet processing technology, the main step in this process involves aluminium hydroxide reaction with hydrofluoric acid to form aluminium fluoride as per the reaction.
  • Al(OH)3 + 3HF → AlF3 + 3H2O
  1. Hydrofluoric acid treated with ammonium aluminium sulphate to produce AlF3 at 650 oC under vacuum.
  2. Reaction between aluminium chloride and fluorine gas generate AlF3 powder with particle size ranging from 50-500 A.
  3. From hydrofluosilicic acid, a byproduct of phosphate fertilizer plant. Phosphoric acid manufacturing unit in phosphate fertilizer plants uses phosphate rock as raw material. Phosphate rock contains 3 to 4% of fluorine even after beneficiation step.  During rock treatment step sulphuric acid used as a reagent. Fluorine in the form of calcium fluosilicate and silicontetrafluoride reacts with sulphuric acid forming hydrofluoscilicic acid.
  • CaSiF6 + H2SO4→ H2SiF6 + CaSo4

 

The so formed hydrofluosilicic acid is treated with aluminium hydroxide at 100 oC to give aluminium fluoride as per the reaction.

  • H2SiF6 + 2Al(OH)3 → 2AlF3 + SiO2 + 4H2O

A drum filter continuously filters out silica from the product solution. The filtrate sent to crystallizer to obtain crystal of aluminium fluoride at 95 oC. The slurry from the crystallizer is centrifuged and the cake from the centrifuge is dried and calcined. Calcination takes place at 600 oC.  The product cooled to room temperature before packing.