Copper dressing

Lead bullion flows from the tapping facility via a Y launder into either of two steel ladles lined with castable refractory and located in a pit adjacent to the furnace. The ladles are usually around 10 t in capacity and are handled by overhead gantry crane, transporting the ladles to the copper dressing operation. 

In some cases special removal steps are added, such as tellurium removal, where these elements are present in significant amounts in the ores treated. Also, particular smelters may have less than the full range of separation stages depending on the impurities present and the smelter s source of lead concentrates for instance bismuth removal can often be omitted. However, in all cases copper dressing and caustic refining are required. 

This concept can be extended to the direct application of sodium metal to the copper dressing kettles where the addition of sodium redistributes the sulfides and arsenides and enhances dross fluidity to facilitate separation of matte fiom lead bulUon. A separate speiss phase also tends to form but requires the addition of sodium at least equivalent to 100 per cent of the stoichiometric amount corresponding with sulfur in excess of CU2S. The reactions with sodium form Na2S, Na3As and Na3Sb in that order. This can be a useful means of arsenic and antimony separation if present in only small amounts. 

Smelting processes are assumed to terminate at the production of crude bullion, excluding the copper dressing operation which has been included in the refining operations. 

Flotation or froth flotation is a physicochemical property-based separation process. It is widely utilised in the area of mineral processing also known as ore dressing and mineral beneftciation for mineral concentration. In addition to the mining and metallurgical industries, flotation also finds appHcations in sewage treatment, water purification, bitumen recovery from tar sands, and coal desulfurization. Nearly one biUion tons of ore are treated by this process aimuaHy in the world. Phosphate rock, precious metals, lead, zinc, copper, molybdenum, and tin-containing ores as well as coal are treated routinely by this process some flotation plants treat 200,000 tons of ore per day (see Mineral recovery and processing). Various aspects of flotation theory and practice have been treated in books and reviews (1 9). 

Dressing. The impure lead bulhon, produced from any of the smelting processes, is cooled to remove dissolved copper prior to the refining operation. The operation is referred to as copper drossing, and is performed in one or two 250 t cast-iron ketdes. The process consists of skimming off the dross, stirring the lead, and reskimming. 

Precipita.tlon, In the simplest case, the solubihty of an impurity in the Hquid metal changes with temperature. Thus the impurity may precipitate as a sohd phase upon cooling. For instance, the removal of iron from tin and of copper from lead are achieved by precipitation. When the soHd is lighter than the Hquid, it floats as a dross on the surface of the melt where it is easily removed by scraping. The process is called dressing. 

The dross is removed and fed into a dross furnace for recovery of the nonlead mineral values. To enhance copper recovery, dressed lead bullion is treated by adding sulfur-bearing materials, zinc, and/or aluminum, lowering the copper content to approximately 0.01%. 

Corrosion was observed on the aluminum pressure plates and dress-caps that hold the glazing in place on a curtain-walled building. The dress-caps (which have L-shaped cross-sections) were externally clad with thin copper sheet. 

Figure 7.27 A pressure plate (bottom) and a dress-cap (top). The dress cap is clad with copper sheet. The pressure plate is fitted with two rubber inserts. (Reproduced from COM 1999 and 2005 with permission from the Metallurgy Society of ClM)...

In order to hide the aluminum extrusions, rubber strips and screws (dress-caps) were fitted over the top of the pressure plates. They were also aluminum extrusions with L-shaped cross-sections. For aesthetic reasons, the original building design required the dress-caps to be externally clad with thin copper sheet. The copper sheet was mechanically attached by rolling over the two longitudinal edges onto the internal surfaces of the dress-cap. Figure 7.27 shows a pressure plate and one of the dress-caps. 

Several years after the building was constructed, it was noticed that some of the copper cladding was separating from the dress caps, particularly near the base of the building. 

The new dress-cap substrate material should be either fiber-reinforced plastic (FRP) or Type 316 stainless steel. Being a nonmetallic insulator, FRP would eliminate any possibility of galvanic corrosion. Type 316 stainless steel demonstrates good passivity in urban atmospheres and has been successfully used in contact with copper.1... 

Epitome of Process.—The ore is first dressed, roasted, and then smelted in blast or reverberatory furnaces to a ferruginous matte consisting essentially of sulphides of copper, nickel, and iron. This is then oxidised in a blast of air in a converter in an analogous manner to the production of steel by the basic Bessemer process. By this means practically all the iron is removed, and as much sulphur as possible without excessive loss of nickel. On an average the product contains approximately ... 

Prohibited All other fungicides All herbicides are questionable and should not be used on crops to be sold as organically grown All pesticides that are persistent, cumulative or toxic to other species Most seed dressings are questionable and should not be used on crops to be sold as organically grown, with the possible exception of copper sulphate fungicide... 

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