Abstract: A process for transferring environmentally harmful substances which are easily leachable from openly discarded waste material, and which to a large proportion consists of inorganic material, such as spent spot linings for aluminum electrolysis cells, into gaseous form or into leach stable compounds, includes the steps of heating that the material in finely ground form is heated and in that reagents such as silica, water and oxygen are added in a cyclone furnace (1) which includes a heat source (2) for example a plasma generator, and a cylindrical furnace vessel (10). By feeding the waste material and the reagents via a mixing and prereaction chamber (3) which is located between the high temperature source and the vessel (10), a very high proportion of the added materials are reacted in the furnace.

Abstract: A method for melting iron and steel scrap wherein scrap is fed through a shaft furnace countercurrent to a reducing gas. The reducing gas is formed by passing air through a plasma generator and injecting coal and/or hydrocarbon into the hot air so that the ratio (CO.sub.2 +H.sub.2 O)/(CO.sub.2 +H.sub.2 O+CO+H.sub.2) of the resulting gas becomes less than 0.2. The energy needed for melting is supplied as sensible heat of the reducing gas. The energy for preheating the scrap is supplied by introducing oxygen containing gas into the preheating zone at a plurality of positions along the flow path of the reducing gas to provide stepwise combustion of the reducing gas. The introduction of the oxygen containing gas at said plurality of positions is balanced to keep the gas reducing to the metal scrap at scrap temperatures above 1000.degree. C., and preferably even above 800.degree. C.

Abstract: To separate zinc out of a hot gas containing zinc vapour, a flow of lead is circulated in counterflow to the gas in a condenser. Heat from the lead flow from the condenser is transmitted to a chamber from which lead is transferred to the condenser. The lead flow from the condenser is cooled in known manner to a temperature at which its zinc saturation solubility is lower than its zinc content, thus causing precipitatioin of the zinc. The precipitated zinc is then separated off. The cooled flow of lead, poor in zinc, is transferred to the chamber for heating by the heat transmitted thereto so that the lead flow heated in this way and supplied to the condenser acquires a zinc saturation solubility higher than its zinc content.