Abstract: In order to recover in an environmentally sound and economic manner used hardening shop salts which contain nitrate-nitrite, the salts, comminuted to particle sizes of from 1 to 50 mm, are dissolved in a mixture of nitric acid and hydrogen peroxide without nitrogen oxides arising, and, by evaporation and cooling, potassium nitrate, sodium chloride, and sodium nitrate are obtained sequentially by fractional crystallization.

Abstract: The process for environmentally acceptable and economical recovery of chloride salts from hardening-shop used salts utilizing the steps of leaching of the used salt, detoxification of the cyanide and selective crystallization of the individual chloride salts. The process is characterized in that all the chloride salts that are present in the hardening-shop used salt are recovered in pure form.

Abstract: Flawless nitrating layers are obtained during the nitro-carburizing of components made from steels which form passive layers in salt baths if these components are first pre-treated in an oxidizing salt melt at 300.degree. to 500.degree. C. prior to the nitro-carburizing process.

Abstract: In a filter unit (25) and apparatus for desludging salt baths (1), which is flooded at least partially by the salt bath and is in working association with the upper end of a riser tube (23), the bath fluid to be desludged being driven, by means of a compressed air stream, for example, through the riser tube (23) toward the filter unit (9, 25), the filter cloth packet is made of woven wire of a nonferrous metal, preferably an alloy based on aluminum, nickel or titanium, and is surrounded by a filter frame (14), the frame (14) being shaped into a shallow, pyramidal frustum-shaped funnel (18) pointing toward the bottom of the vat, its apical bottom end being provided with a closable opening (19).

Abstract: A method for the preparation of a salt mixture useful for hardening steel parts, including of potassium cyanate, potassium carbonate and sodium carbonate, wherein 2.2 to 2.3 moles of urea is first reacted with 1 mole of potassium carbonate to form potassium cyanate. The escaping ammonia is converted with formaldehyde into hexamethylenetetramine. The reaction product, which is potassium cyanate and potassium carbonate, is ground, mixed with powdered sodium carbonate and pressed at between 80.degree. and 230.degree. C. into shaped pieces.