╨╧рб▒с>■  -/■   ,                                                                                                                                                                                                                                                                                                                                                                                                                                                ье┴3 Ё┐Hbjbj"&bvbvР      l┤┤┤┤┤┤┤╚ *╚йЄJJJJJJJJ$Ы ╗ ┌6-┤JJJJJ6╥┤┤JJc╥╥╥J6┤J┤J╥J╥>╥┤┤J> ЁW┐є╞О╞╚VА0y0йХ ░"Х ╥╚╚┤┤┤┤┘The old smelting method, in use from the beginning in 1646 to 1887. Arne Espelund The ore brought from the mines to the smelting works as lumps consisted of the copperbearing mineral chalcopyrite CuFeS2 and other sulphide minerals such as pyrite FeS2 or pyrrhotite FeS, together with gangue minerals. The ore was considered to be rich if it contained around 5% copper. The purpose of the smelting was to make pure copper with a maximum output. The ore had to go through two steps of smelting. In the first step copper was enriched in a low-melting mixture of sulphides named copper matte. As a preparation for the smelting the ore had to be roasted, so that some of the sulphur in the ore was replaced by oxygen. This first roasting took place in large heaps, about 5 m wide, 2.5 m high and with varying length. The ore was placed on wood, which was ignited. Later sulphide in the ore took over the role as fuel. This roasting lasted for a few weeks. The lumps maintained their shape. The outside of each piece consisted mainly of oxides while sulphur was retained in the center. Smelting of the roasted ore resulting in copper matte took place in a shaft furnace, fired with charcoal. In this furnace quartz SiO2 was added so that a major part of the iron as an oxide formed a silicate slag together with the gangue minerals. The copper matte, now containing some 20 % copper and 30% sulphur, and the lighter slag, with about 0.5% Cu were tapped as two separate liquids, the matte being heavier than the slag. Notice the enrichment of copper in the matte! The intermediate product copper matte had to be roasted anew in order to remove the rest of the sulphur. This roasting took place in a series of stalls, 2 Ц 2.5 m wide. Plates of matte were placed on wood, which was allowed to burn down. By transferring the matte from one stall to the next, this roasting was repeated several times, aiming at a minimum of sulphur. Both copper and the remainder of iron now should be present as oxides. The product of this secondary roasting was charged into a second, charcoal-fired shaft furnace, again with addition of some quartz. This smelting reminded of the smelting to pig iron in the iron industry. The product, named black copper, still contained some impurities. All the larger smelting works has a fifth step, an oxidizing refining (German Gahren) which required great skill. Now the trace of remaining iron was oxidized and slagged by means of addition of a little sand. After skimming of the slag refined copper was taken out as plates after addition of some water. To sum up: the smelting consisted of up to five steps: first roasting in large heaps - replacing some sulphur by oxygen smelting in a matte smelting shaft furnaces, to matte and a slag, which was discarded second roasting in stalls Ц removing the remaining sulphur black copper smelting in a shaft furnace, to black copper and slag (refining in charcoal-fired kettles) All of these operations are shown as models in the smelting works. An important feature was the return of the copper-rich slag from the black copper smelting to the matte smelting furnace. The number of matte smelting furnaces might be 3-4 while they needed only 1-2 black copper furnaces. At smaller copper works they might smelt matte for e.g. three weeks and black copper for 1 week, in one and the same furnace after a slight modification of the hearth. The firing of charcoal in the smelting furnaces required a strong blast, achieved by transfer of power from the running water in a river via a water wheel to bellows. The new smelting method As a result of the improvement in the Continental iron industry, a УBessemer processФ was developed in France around 1880 for this type of copper works. It was introduced at Roros in the year 1887. The advantages were 1) a greatly improved fuel economy 2) simplicity and 3) a high reaction rate. In the old smelting process heat was generated by combustion of wood and charcoal (towards the end replaced by imported coke). In the new process coke was used only in step No. 2, in which matte was produced as before. A new type: a water jacket furnace, based upon an American model was built. This matte was transferred as a liquid to a converter, which had the shape of a barrel and was equipped with tuyшres placed lengthwise. Now air was blown into the liquid matte. At first the iron in the matte was oxidized and slagged off by means of added quartz sand. After a while the melt consisted of white metal (Cu2S), which was finally blown to metallic copper, which was tapped and cast into large bars by tilting the converter to the right position. During cooling of the metal blisters developed due to gas evolution. Therefore a refining furnace was built. Now dissolved oxygen was removed by a slight reduction by means of wooden poles. The refined copper was cast into bars with the stamp of Roros Copper Works R B& V Flotation The next improvement was the introduction of flotation at Storvarts in the year 1926. Now the ore had to be crushed and milled, before addition of some oil and separation in flotation cells. The new product was a fine-grained concentrate with a copper content around 25%. Primary roasting no longer was required. However, the concentrate had to be agglomerated into briquettes before charging to the matte smelting furnace. Broadly speaking this was the practice until 1953, when the smelting works was hit by a fire. 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