This invention is directed to a pyrometallurgical process for material that may be metal-containing waste with the metal compounds in part being reduced and evaporated and in part remaining in the liquid slag. The smelting conditions are reducing to the extent that metal oxides such as those of zinc, cadmium, lead, tin and the like are reduced and the metals or metal compounds formed pass into the vapour phase and are discharged with the gas phase. Preferably, the waste materials contain a major fraction of organic material, since this wholly or partially obviates the need to use a separate fuel. An example of this is the solid residue which remains after a pyrolysis step. This contains large amounts of carbon and additionally an inorganic fraction. Sewage sludge also fits into this category. If these materials are processed in a fossil fuel-fired smelter, difficulties may arise, however. This is because such materials present the problem that carbon particles are not present in molten form and therefore require a relatively long time for complete combustion. The as yet uncombusted carbon particles will float on the slag formed, which may have an adverse effect on the quality of the ultimate slag, since carbon forms weak spots in the crystallized slag. In addition, inorganic constituents may remain trapped in the carbon, whereas it would be preferable for these to be dissolved in the slag to prevent leaching of the latter or even to prevent it. Moreover, the caloric content of the unreacted carbon is not utilized.
To solve the abovementioned problem, the German Offenlegungsschift 36 29 661 proposes that additional air be introduced in the bottom section of the smelting reactor just above the molten slag. The oxygen from this air then serves the purpose of completely combusting the carbon particles. According to this method, however, afterburning is carried to completion, and the conditions in the smelting reactor are therefore oxidizing. This entails two drawbacks. Firstly, a number of metals cannot then be completely removed from the slag (such as zinc, lead, tin, arsenic and the like), and secondly it is thus not possible to produce any fuel gas or synthesis gas in the smelter.
German Offenlegungsschrift 36 38 204 A discloses a process for processing of metal containing substances like ore concentrates according to which the substances are smelted in the oxidative atmosphere of a smelting cyclone furnace. For recovering the valuable metals therefrom the obtained smelt is then finally processed by blowing a reducing gas on the smelt present in a blowing reactor positioned after the smelting cyclone furnace. The waste gas of the blowing reactor being mainly carbon monoxide, hydrogen, metal vapour or metal compounds in vapour form is led to the smelting cyclone furnace counter-currently with respect to the flow direction of the smelt. This waste gas can be burned therein providing a part of the heat requirement of the smelting cyclone furnace. So, the production of a usuable synthesis gas, which can be obtained after removal of the evaporated metals or metal compounds from the flue gas is missing in the process according to said German Offenlegungsschrift 36 38 204.
German Offenlegungsschrift 29 22 189 being discussed as prior art in the abovementioned German Offenlegungsschrift 36 28 204, discloses a process for the processing of smeltable substances like sulfidic ore concentrate and simultaneously the winning of valuable metals, wherein for the final processing of the smelt reducing gases optionally preceded by oxidizing or neutral gases respectively were blown through several supply ducts virtually perpendicularly on the smelt in a blowing reactor. The slag formed and the specifically heavier metal phase are then separated from each other.
In German Offenlegungsschrift 41 42 401 a process is described for controlling the heating of a furnace based on one or more burners, for instance a smelting furnace for metals or glass, wherein the formation of nitrogen oxides is reduced. However, in this process, leading to an ultimately total combustion, no supply ducts are used, through which gases having a high velocity can be blown against the surface of the smelt.
Further German Offenlegungsschrift 23 48 105 discloses a thermal process for the continuous extraction of metals and/or metal compounds from ores, concentrates thereof etc., wherein the liquid product from the furnace is separated by means of centrifugal forces in a metal smelt on the one hand and slags on the other hand.
It is an object of the invention to develop a process for working up metal-containing waste material which may also contain organic material, for example pyrolysis residues, which process does not suffer the drawbacks involved in the processes known in the prior art.