phosphate expressed as p 2 o 5 and greater than 500 parts per million of ammonium ion the fluoride component is believed to be comprised primarily of sif 6 2 the sif 6 2 in the wastewater solution is removed therefrom by reacting it with nh 4 2 so 4 to form nh 4 2 sif 6 in this regard it has been observed unexpectedly that in addition to reacting with sif 6 2 to form nh 4 2 sif 6 the nh 4 2 so 4 when used in excess actually reduces the solubility of nh 4 2 sif 6 in water thus enabling relatively pure nh 4 2 sif 6 to be precipitated from the solution upon the concentration thereof in this regard while a portion of such decrease in solubility might be attributed to the common ion effect the degree of purity of the precipitate as well as the extent to which the salting out occurs are greater than what would normally be expected for this purpose an amount of nh 4 2 so 4 in excess of the stoichiometric amount required for reaction with the sif 6 2 should be employed in general therefore 1 5 to 5 0 and preferably 1 5 to 3 0 moles of nh 4 2 so 4 should be added per mole of sif 6 2 recovered from the wastewater due to the salting out effect of the nh 4 2 so 4 present in the wastewater nh 4 2 sif 6 precipitates therefrom when the wastewater is concentrated the overall process for producing hydrofluoric acid from an acidic process wastewater is illustrated schematically in fig1 initially the.