Abstract: The invention relates to a method for recovering useable products from waste products deriving from the manufacture of aluminium fluoride on the basis of aluminium hydroxide and fluosilicic acid. Mother liquors and washing water from a scrubber in said process, which solutions contain aluminium, silica, fluorine, and phosphorous is reacted in a first step with sodium ions at pH 2-3, and a temperature of 50.degree.-100.degree. C. to give a precipitate of sodium fluoroaluminate, which is isolated. The filtrate from said first step can be reacted with the silica waste product obtained in the above mentioned aluminium fluoride manufacture.

Abstract: The present invention relates to a method for purifying silica waste obtained in the manufacture of aluminium fluoride from hexafluosilicic acid and aluminium hydroxide, whereby the silica, is subjected to an acidic leaching at a pH below 3 to leach out part of the fluorine and substantially all the aluminium present in said waste, and is thereafter subjected to an alkaline leaching at pH 8.5-11.5 to leach out remaining fluorine present in said waste. The leachings are preferably carried out at elevated temperatures, normally 60.degree.-90.degree. C., and for a time sufficient to considerably reduce the contents of aluminium and fluorine, normally 1-3 hrs.The silica obtained is highly reactive and can be used as such or transformed into sodium silicate by a reaction with sodium hydroxide. The contents of fluorine and aluminium can be transferred to a process for the production of cryolite or similar compounds.

Abstract: The invention relates to a method for recovering useable products from waste products deriving from the manufacture of aluminium fluoride on the basis of aluminium hydroxide and fluosilicic acid. Silica contaminated with fluorine and aluminium and obtained in the manufacture of aluminium fluoride is dissolved with a strongly basic hydroxide, whereafter the first solution obtained is mixed with a second solution, obtained by dissolving aluminium hydroxide with a strongly basic hydroxide, and with waste mother liquor and optionally also washing water from the manufacture of aluminium fluoride, in such proportions that the pH-value of the mixture is from about 10-14.