Patent GB-380493-A (GB)
Title: Process for recovering metals, such as tin, lead, antimony and bismuth or alloys thereof from substances which contain same and which may also contain more volatile metals such as arsenic, cadmium and zinc
IPC: C22B5/00
Filed: 1931-06-11
Abstract: In a process for the recovery of metals such as tin, lead, antimony, bismuth or alloys of two or more of these metals, oxidic material is mixed with solid fuel and fluxes such as sodium carbonate, borax, waterglass or tin slag and subjected to a reduction treatment at temperatures at which the metal or alloy to be recovered, but not the residue of the charge is melted, in an elongated rotary drum or rocking furnace traversed by flame gases in such a manner that the bulk of the oxide is first reduced in a reducing zone, the metal that is still retained in the residues being then separated in a succeeding finishing zone.  Oxides of volatile metals such as zinc, arsenic, cadmium, &c. if present in the charge are also reduced to metals which in part pass into the molten tin, lead, &c., the remainder vaporizing and passing out of the furnace with the gases. Sulphur is kept as low as possible by preroasting the charge.  The separation of the molten metal from the charge is improved by increasing the action of the difference of the adhesive capacity of the reduced metal in relation to the charge and to the furnace walls, and the difference in specific gravity between the reduced metal and the charge, this being effected by adapting the dimensions and speed of the furnace, the depth of the charge and the working temperature to the slagging properties of the particular charge treated.  A furnace suitable for carrying out the process comprises a rotary drum 1, lined with ordinary refractory or with the material being treated, for example moulded bricks of tin oxide and binding media or of the reducing agent.  The drum is driven by mechanism 4 and heated by a burner 5.  Air for combustion enters openings 6, 7.  Heating appliances may also be fitted at the other end of the furnace and supplemented by electrical heating means.  The charge, including, if desired, a large excess of reducing agent is fed from a hopper 9 and is preheated in a zone 20 and reduced in a zone 13 the metal running down to form a bath in a sump 16 which may be tapped at intervals into a receptacle 18.  A drum that is widened at the discharge end may be used.  Finely divided metal is recovered in a concentration zone 14 where further reduction of the charge may also take place particularly if a large <PICT:0380493/III/1> excess of reducing agent is added at the start or by adding solid or liquid reducing agent or by increasing the working temperature in the zone.  The addition of gaseous or liquid combustible substances increases the reducing effect of the atmosphere in the furnace as does also the introduction of oxygen to burn part of the reducing agent.  The slag may, if desired, be melted in front of the burner 5 and discharged into a receptacle 17.  The gases pass through a chamber 10 and fume separator 11 to a flue 12.  A chamber 8 at the discharge end is also connected to the separator 11 to recover fine dust and metal fume. Volatilized oxides of zinc, lead, tin, &c. are treated for the recovery of zinc and other metals in a muffle or an electric furnace, preferably after first sintering the oxides or making them into a paste with a flux such as sodium carbonate, borax, &c., and reducing carbon.  The zinc content of the recovered metal is determined by the working temperature and reducing atmosphere of the furnace and by adding zinciferous material to the original charge.  The presence of zinc is desirable for the further refining of the alloys.