The invention pertains to a method of inertising free soluble impurities of phosphates and/or fluoride ions, in phosphogypsum, for use in commercial and industrial applications. The Phosphogypsum is pre-conditioned over an extended period of time separately or treated along with standard constituents by spraying, interblending or intergrinding during the process of manufacture, with alkyl, alkenyl and/or alkanol derivatives of ammonia, either individually or in combination with one another, to form stable intermediary phosphates and/or fluoride salts of the derivatives of ammonia.