SHG zinc

Zinc is extracted from the purified solution in cells using lead/silver alloy anodes and aluminum cathodes at a current density of 38-60 amperes/square foot (400-650 amperes/square meter) The product is normally SHG zinc, particularly if strontium carbonate is added and/or lead/silver anodes of greater than 0.596 silver content are used. After deposition of 24 to 72 horns, the cathodes are removed from the cells and the zinc is stripped by automatic machines in modem plants, melted, and cast for market. The move to automated handling of large cathodes was a major factor in lowering the overall labor requirement in producing zinc. 

The capacity was 170,000 tonnes of zinc per year after the 1988 modernisation of the plant. Today the current roasting capacity has been increased to about 190,000 tonnes, see Figure 1. After the 1998 expansion, based on the direct leaching of zinc concentrates, the new total capacity of the Kokkola plant is about 225,000 tonnes of SHG zinc (99.995 %) per year. The latest on-going expansion will further increase both the leaching and roasting capacity to... 

Crude zinc from the lead splash condenser is refined separately to produce SHG zinc. 

The British company Reunion Mining Pic (RM) performed a techno-economical feasibility study for the Skorpion mine (Namibia) during 1S 7 and 1998. At that time, RM entered in contact with the R D Division of Tunicas Reunidas S.A. (TR). The objective was to apply the modified ZINCEX process (MZP) to the treatment of Skorpion ore to produce SHG zinc. One of the most important stages of the feasibility study was the piloting of key sections of the process namely, leaching, solvent extraction and electrowinning. 

Tecnicas Reunidas R D Division, SHG Zinc Plant by the Modified ZINCEX Process and Modified ZINCEX Process Applied on Sanyati Copper PLS , Report ITRyP4696/1998. Client Munyati Mining, 1998. 

Laboratory and field studies by Crennell and Wheeler (1956, 1958) showed that an iron content level of more than a few parts per million caused passivation of zinc and that no other common impurities in zinc were of importance to anode performance. These studies showed that the addition of 1% aluminum was beneficial and that 0.5% aluminum plus 0.5% silicon significantly increased a zinc anode s tolerance for iron and also produced a finer grain structure than was obtained with SHG zinc with 0.0014% maximum iron. 

Comparison of British Standard for SHG Zinc with Typical Skorpion Zinc Cathode Analysis... 

Many types of furnace are available to produce vapor of the required purity from various raw materials and obtain a high yield of zinc. Pure zinc (super high grade, SHG high grade, HG) or, to an increasing extent, metal residues (e.g., scrap zinc,... 

Electrolytic Process—in which oxidized zinc concentrates are leached in sulfuric acid and then electrolyzed to plate SHG (special high-grade zinc metal) on the cathode and to regenerate the add on the anode. 

Deposited zinc sheets are stripped and are s it to melting furnaces to cast SHG slabs of 20 kg. Those slabs are bundled in about 1 ton lots, and the production data, such as the date, furnace number, lot number and weight are printed with a fully automated system. 

The high performance of the process was proven in the pilot plant campaigns, illustrated in Figures 3 and 4. Performance was demonstrated by a high zinc recovery, low power consumption, and the high quality of the SHG Zn produced. Analyses of zinc plates produced in the Skorpion pilot plant on May 9,1998 and certified by Union Miniere are ... 

The success of the SX process chemistry can be assessed with reference to the typical quality of the zinc cathode produced, which consistently exceeds SHG grade due to the high electrolyte purity. Table 5.5 shows the specification for SHG cathode and a typical analysis of the Skorpion Zinc product. 

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