ZERON 100 Mining Industry - Rolled Alloys

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PD5500 in Zeron 100 is 3.5m diameter, 4.5m tall and 20mm thick and it has been inservice with a UK pigments manufacturer since 1996 with no problems. Larger vesselshave been manufactured to ASME VIII division I, such as a mixed sulphides vessel at anickel laterite mine, mine that was ~ 3m diameter and 20m long.Zeron 100 is readily welded by all the commonly used arc welding processes. It isusually welded with Zeron 100X consumables, which contain extra nickel to ensure thecorrect phase balance of the weld metal in the as- welded condition. Like all high alloystainless steels, Zeron 100 requires welders experienced in stainless steel fabricationworking to approved and qualified procedures.Supply is not a problem because Zeron 100 is readily available in all the common productforms, including castings, pipes, fittings, flanges, plates, bar, billet, fasteners etc. A largestock is currently held in all these product forms in RA Materials, Manchester warehouse.3. CORROSION3.1 Acid LeachDuring many mining operations leaching is often carried out with sulphuric acid. Zeron100 has excellent resistance to sulphuric acid, better than many of the alloys in Table 1,including other superduplex stainless steels such as UNS S32750, as shown by the isocorrosioncurves (0.1mm/y) in Figure 1. This is because the latter alloy does not containany copper or tungsten.Sulphuric acid used in extraction processes often contains impurities and a common oneis the chloride ion. Figure 2 shows the iso-corrosion curves (0.1mm/y) for Zeron 100 andsome other common stainless steels in sulphuric acid containing 2,000 mg/l chlorides. Itcan be seen that Zeron 100 has superior corrosion resistance not only to the commonstainless steels, but also compared with other high alloy stainless steels such as S31254(a 6% Mo super austenitic) and S32750 (a 25% Cr superduplex).There are other ions which could be present and which can influence corrosionresistance. Other halides, such as fluorides and bromides, will decrease corrosionresistance in a similar manner to chlorides. Oxidising species, such as ferric and cupricions, have a beneficial effect and increase corrosion resistance. Figure 3 shows theeffect of 50 mg/l ferric ions and 100 mg/l cupric ions on the iso-corrosion curve of Zeron100 in sulphuric acid. However, halide ions are often also present with these oxidisersand so the exact concentration of each will determine the corrosion resistance. However,Zeron 100 consistently performs well in such solutions.In some extraction processes hydrochloric acid is preferred and Zeron 100 has goodresistance to dilute acid at high temperature as shown in Figure 4, especially whencompared with other grades of stainless steel.Many processes involving sulphide ores utilise oxygen sparging at elevated temperaturesin acid environments. An autoclave test was carried out under the following conditions tosimulate a typical environment:NaClMgSO 4NiSO 414 g/l15 g/l52 g/lCopyright © Rolled Alloys 2008Report No. TN1346Issue No. 4Page 6 of 22
pH 2Temperature 100 o CPressure 10 bar (O 2 )Samples of Zeron 100 were tested to assess resistance to general corrosion, crevicecorrosion and stress corrosion cracking, with exposure for 3 weeks. The corrosion ratewas ~ 0.03 mm/y and there were no signs of crevice corrosion or stress corrosioncracking.Note that in oxidisation pressure leach applications, the conditions become moreaggressive as the chloride and oxidiser (such as ferric and cupric ions) concentrationsincrease. When both oxidisers and chlorides are at high concentrations, it is possible toget localised pitting, particularly in shielded areas. It is important to consider each projectindividually under its own specific conditions.3.2 High Pressure Acid LeachingHigh pressure acid leaching of metals from ores has been used in a number of locationsaround the world and it is being used for extracting nickel from the laterite ores inWestern Australia. Plants in other parts of the world are currently under construction. Inthis method crushed ore is heated to temperatures of about 250 o C and the nickel isextracted with sulphuric acid at about 50 bar pressure.In Western Australia there is a shortage of fresh surface water in sufficient quantities forthis process, although there are numerous boreholes producing high chloride brines (15to 150 g/l chloride). To use conventional plant materials it would be necessary to reducethe salinity of the water substantially by desalination. This would be extremely expensive,both in terms of the cost of the plant and its operating costs. The alternative is to use theborehole water as it is and build the plant of suitable corrosion resistant materials.Figure 5 shows a simplified schematic diagram of the ore processing chain. Two heatingand cooling stages are shown, but in practice there could be four or more stages prior toand after the main autoclave. During heating, a mixture of crushed ore and water issteam heated in stages until it is injected into the main autoclave. Sulphuric acid is addedeither to the autoclave or immediately prior to it. After reaction in the autoclave theresidual slurry is progressively cooled through a series of flash tanks. Steam extractedfrom each tank is used to provide heat during the heating stages (Figure 5). Followingthis the slurry is at about 100 o C and it must be further cooled, separated and neutralisedprior to extraction of the nickel.3.2.1 Heater FluidsIn the directly heated vessels, as shown in Figure 5, the steam from the flash tank stripsmost of the oxygen from the incoming slurry, but the carry over of acid can mean that thepH could drop to 3. Under severe upset conditions even lower pH’s have beenpostulated. A series of autoclave tests was conducted in a simulated laterite slurry of thefollowing composition at different pH’s at 200 o C, a typical autoclave injectiontemperature:-Copyright © Rolled Alloys 2008Report No. TN1346Issue No. 4Page 7 of 22
Page 1: REPORTTITLEZeron 100 Superduplex St
Page 8 and 9: MgSO 4 - 15g/lFe 2 (SO 4 ) 3 - 150
Page 10 and 11: In the copper mining industry the e
Page 12 and 13: TABLE 1 The composition of some sta
Page 14 and 15: TABLE 4The corrosion of Zeron 100 i
Page 16 and 17: TABLE 7Some applications of Zeron 1
Page 18 and 19: FIGURE 3 Iso-corrosion curves (0.1m
Page 20 and 21: FIGURE 6 Erosion of several alloys
Page 22: Figure 9 Mixed sulphides vessel for

ZERON 100 Mining Industry - Rolled Alloys

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