Zinc oxide slurry process

Zinc electrodes for secondary silver-zinc batteries are made by one of three general methods the dry-powder process, the slurry-pasted process, or the electroformed process The active material used in any of the processes for the manufacture of electrodes is a finely divided zinc oxide powder, USP grade 12. 

This pigment, also called zinc yellow, is produced by reacting an aqueous slurry of zinc oxide or hydroxide with dissolved chromate ions, followed by neutralization, or by precipitation of dissolved zinc salts with dissolved chromate salts, followed by washing, filtration, drying, and milling processes [5.56]. Previously zinc yellow used to hold a major share of the anticorrosive pigment market... 

The process is carried out in a simple, vertical bubble contactor as shown in Figure 16-7. The contactor is equipped with inlet and outlet gas nozzles,. slurry feed and overflow nozzles, a drain, a manway, a mist eliminator, and a gas distributor. Gas bubbles rise from the distributor and provide the agitation to keep the zinc oxide particles in suspension. 

Direct l eaching of Concentrates. Sherri tt Gordon Mines, Ltd., has adapted the process first used on nickel sulfide ores to zinc sulfide oxidation with air in aqueous slurry under pressure (42,43). The concentrates are leached direcdy with return acid from the cells and the sulfide is converted to free sulfur ... 

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

The process begins with a weak acid leach (pH 1.5-1.8) followed by a pH bump to 3.8-4.0 for iron, silica, arsenic and antimony precipitation. The slurry is thickened, and the solid residues are filtered and washed to recover water-soluble zinc in two stages of American disk filters. This filtration step is being upgraded as described in a following section. These iron-rich residues are then repulped and combed with the residue slurry from the oxide leaching circuit and are pumped to the smelter where the slurry is filtered, combined with other materials and process in the JCIVCET furnace. 

Significant development has occurred within the industry over the last several years with respect to liquid-phase processes. One example of this process that is reasonably close to commercialization is that developed by Air Products. A pilot unit has been operated for several years at their La Porte, Texas location. The process is characterized briefly as using an inert hydrocarbon reaction medium in the liquid phase to absorb the synthesis heat of reaction conventional copper-zinc catalyst is fed to the reactor system as a slurry. This type of process appears to be particularly well suited to substoichiometric feeds (hi earbon eontent), such as those produced by partial oxidation or coal gasification. The Air Products process has been extensively deseribed in patent literature [14]. Kinetie data and liquid-phase reaetion systems have also been extensively diseussed by Lee in Methanol Synthesis Technology [15]. 

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