Abstract: A method of obtaining or recovering hydrofluoric acid from metal fluorides and solutions containing such, e.g. pickling solutions. In this procedure heavy metal fluorides are brought into contact with water vapor at 200.degree. C. to 800.degree. C., with an overall pressure of about 1 bar keeping the vapor partial pressure in a sufficiently linear relationship with the temperature in this range at a minimum of 0.9 bar at 400.degree. C. and at a minimum of 0.5 bar at 600.degree. C., separating the solid reaction material from the gaseous phase while still hot and obtaining aqueous hydrofluoric acid from the latter by--preferably indirect--cooling.

Abstract: Apparatus is disclosed for treating pickling solutions used for pickling metal, such as iron, steel, special alloys, or the like. In a preferred embodiment, the apparatus includes an evaporator, a condensor, a crystallizer, a crystal-separating device, fittings and conduits for connection to the metal-treating plant, and a device for automatically controlling the evaporation rate in the evaporator. The evaporator includes a flow channel, vapor removal connection above the liquid level in the flow channel, an inlet and outlet for the solution being treated, and a plurality of electrodes for directly applying AC current to the solution. The electrodes are mounted spaced along the length of th flow channel and are completely covered by the solution so as to be out of contact with the vapor. The crystallizer comprises an upright cylindrical vessel having an inlet and an outlet, a driven shaft extending in the center line of the vessel, and is provided with radial ribs.

Abstract: In pickling metal, such as iron, steel, special alloys, or the like, aqueous blends containing hydrofluoric acid and nitric acid are used as pickling solutions; resulting spent pickling solutions are evaporated under controlled conditions, such that the concentrate is supersaturated and contains a predetermined amount of iron; the concentrate is then partially cooled and transferred to a crystallization zone where, under controlled conditions, a crystalline precepitate is formed by cooling the concentrate in two phases; the resulting precipitate is then separated from its mother liquor, and the latter is recycled for use in pickling metals of the aforedescribed type.

Abstract: A process for descaling a metallic body, wherein a heated body is immersed in a bath of a molten oxidizing salt, and subsequently in an electrolyte of an aqueous solution of at least one neutral salt from the group consisting of the chloride, sulfate and nitrate of an alkali metal or ammonium.

Abstract: A process for descaling a metallic body, wherein the body is immersed in a bath of a molten oxidizing salt, and subsequently in an electrolyte of an aqueous solution of at least one neutral salt from the group consisting of the chloride, sulfate and nitrate of an alkali metal or ammonium.

Abstract: A process for descaling a metallic body, wherein the body is immersed in a first electrolyte, and subsequently, in a second electrolyte. The first electrolyte is an aqueous solution having, by weight, at least 60% potassium hydroxide, at least 5% water and no more than 30% potassium nitrate, and a total amount of potassium hydroxide and potassium nitrate of at least 80%. The second electrolyte is an aqueous solution of at least one neutral salt from the group consisting of the chloride, sulfate and nitrate of an alkali metal or ammonium.