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Frequently, the presence of naturally occurring resurfacing ions may interfere with, rather than aid, flotation separation. Where such interference is encountered, it becomes necessary to precipitate or complex those ions to render them inactive. The use of precipitants also may inhibit the formation of the resurfacing ions.
Undesired resurfacing ions are encountered in the treatment of copper-zinc ores and lead-zinc ores containing small amounts of copper minerals. If the copper and zinc sulfides could be ground separately and the added together to a flotation machine, nearly perfect recovery of the copper could be obtained without floating the zinc and by using only lime (or soda ash), xanthate, and a frother.
However, in the treatment of a copper-zinc ore, separate grinding is, of course, impossible. During the grinding stage some copper is dissolved – and it is precipitated on the zinc sulfides. To prevent such activation of the zinc sulfides, the copper may be complexed with cyanide, precipitated with soda ash, or prevented from forming (as well as precipitating) by reducing agents such as sulfites. Frequently, all three of the above reagents may be used. In such cases, the soda ash is added to the grinding stage and the conditioner. This is to prevent the reaction the cyanide with the sulfite.
The advantages of precipitating any interfering ions have also been demonstrated in the flotation o non-sulfide, as well as other sulfide minerals. As the discussion under “Cationic Agents”, page 14 shows, calcium ions, present in all limestone ore pulps, may act as resurfacing activators for silica with fatty acid collectors, or as depressants for pyrite or galena in flotation with xanthates. For this reason, soda ash – which precipitates the calcium ions – is generally used for the flotation of galena, pyrite, fluorspar, or similar minerals. |
