Cathode starting sheets

Decopperized blast furnace bulHon is softened to reduce impurities below 2% before casting as anodes. The electrolyte is a solution of lead fluosUicate [25808-74-6] PhSiF, and free fluosUicic acid [16961 -83-4]. Cathode starting sheets are made from pure electrolytic lead. The concrete electrolytic ceUs are lined with asphalt or a plastic material such as polyethylene. 

The temperature in the ceU is 40°C. Most electrolyte ceUs are equipped with 24 anodes spaced approximately 10 cm apart, center to center 25 cathode starting sheets are used, one at each end and others evenly spaced between the anodes. Current density is typicaUy 15 mA/cm of cathode area ceU voltage ranges from 0.30 to 0.70 V, and a current efficiency of 90—95% is usuaUy realized. 

Centre line anode spacing is commonly 100 mm, resulting in a gap between new anode and cathode surfaces of 34.5 mm with a 1 mm thick cathode starting sheet. The cathode thickness will increase, but the anode thickness will not decrease to the same extent due to the residual slime layer. Hence the gap will decrease with time. If the gap is too small there is an increasing risk of short circuiting between the two electrodes. 

Pure nickel (99.9%) can be produced by electrolytic refining. Generally, an impure metal anode (produced by reducing nickel oxide) and a cathode starting sheet are placed in an acidic electrolytic solution. When a current flows, nickel and other metals are dissolved from the anode. The electrolyte is then removed, purified, and returned to the cathode compartment, where nickel is deposited on the cathode. 

In the electrorefinery, anodes produced from fire-refined copper as described above are dissolved electrolytically in acidic copper sulfate and the copper is deposited on starting sheets to produce cathodes. These operations are carried out in tanks, and refineries are often known as tank houses. The cathodes are sold direcdy or melted and cast into a number of forms. 

The INCO, Thompson plant in Manitoba, Canada, electrolyzes 240 kg sulfide anodes in a sulfate-chloride electrolyte. The approximate composition of the electrolyte is 60 g L x Ni2+, 95 g L 1 SC>42, 35 g L 1 Na+, 60 g L 1 Cl-, and 16 g L 1 H3BO4, and the temperature is 60 °C. Nickel, cobalt, and copper dissolve from the anode, while sulfur, selenium, and the noble metals form an insoluble sludge or slime, from which they can be recovered. The anode sludge contains 95% elemental sulfur, sulfide sulfur, nickel, copper, iron, selenium, and precious metals. Nickel is deposited on to pure nickel starting sheets. The anode cycle is 15 days and the cathode cycle is 5 to 10 days. Electrolysis is carried out at a current density of 240 A m-2 giving a cell voltage of 3 to 6 V [44, 46]. 

The OMG Harjavalta nickel refinery has 126 electrowinning cells, of which 108 are commercial cells and 18 are starting sheet shells. The older cells have 49 insoluble lead anodes and 48 cathodes and the newer cells have 53 anodes and 52 cathodes each. Figure 20 shows the schematic cell construction used at the Harjavalta nickel refinery. The bagged cathodes are nickel starting sheets made by the deposition of nickel for 48 hours onto a titanium mother blank. The deposits are stripped and automatically made up into starting sheets. The purified solution is fed separately to the cathode compartments at... 

The refinery produces both regular nickel cathodes and Falconbridge Crowns . The regular cathodes are produced by plating onto nickel starting sheets. Crowns weighing 30-60 g are round pieces produced by plating nickel onto nonconductive cathode blanks with evenly spaced conductive spots [52, 53]. 

Cathodes are 20 mm greater in dimensions than the anode and are usually 0.7 to 1.0 mm thick as starting sheets, growing to between 12 and 23 mm (120 or 220 kg respectively) depending on the cycle time in comparison with the anode. 

Betts Electrolytic Process. The Betts process starts with lead bullion, which may carry tin, silver, gold, bismuth, copper, antimony, arsenic, selenium, teUurium, and other impurities, but should contain at least 90% lead (6,7). If more than 0.01% tin is present, it is usually removed from the bullion first by means of a tin-drossing operation (see Tin AND TIN ALLOYS, detinning). The lead bullion is cast as plates or anodes, and numerous anodes are set in parallel in each electrolytic ceU. Between the anodes, thin sheets of pure lead are hung from conductor bars to form the cathodes. Several ceUs are connected in series. 

The tank house is divided into commercial and stripper sections. In the latter, one-day deposits are prepared by electrorefining anode copper onto oiled copper, stainless steel, or titanium blanks. These copper sheets are stripped from the blanks and fabricated into starter sheets for the commercial sections as starting cathodes. After 9—15 days, depending on the tank house, hill-term cathodes are pulled and washed and either sent to the casting department or sold direcdy. 

The start area on the plate (strip) is marked with a pencil at the cathodic side. If several samples should be analyzed in the same run, the start areas should have a distance of 1.5-2 cm. A plastic sheet covers the starting zone and the plate is sprayed with Soln. A until it is humid but not wet. 

In the free space between the inner vessel and the outer box, resistance wires are placed to heat the electrolyzer at the start of the process. After the electrolyte has reached a sufficient temperature the electrical heating is disconnected and air, heated to some 230—250 °C, is blown into the space to keep a constant temperature in the bath during the electrolysis. 6 graphite anodes and 7 cathodes made of perforated silver sheet are alternately suspended in the inner vessel. Both cathodes and anodes are inserted into special diaphragms made of electron and perforated at the bottom. They enclose in the form of bells each electrode. The gases liberated during electrolysis are taken off at the top of the bells. The whole assembly of anodes and cathodes is covered by an electron cover. 

Impure copper as obtained by the reduction of its ores contains small amount of other metals like iron, zinc, nickel, silver and gold with which the starting copper ores are associated. A slab of this impure copper is made the anode of an electrolytic cell in which a graphite-coated sheet of pure copper constitutes the cathode, and an aqueous solution of copper sulphate containing sulphuric acid is the electrolyte. Electricity is passed through the cell from a source of direct electric... 

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