Electrowinning flowsheet

Figure 5 A simplified flowsheet and materials balance for the recovery of copper from oxidic and transition ores by heap leaching, solvent extraction and electrowinning.

The most important copper electrowinning production method is heap leaching of oxide copper ores with recovery by solvent extraction and electrowinning (SX-EW process). The general flowsheet of an SX-EW process is shown in Fig. 18. It is a low-cost method of copper recovery. This technology has recently been applied successfully to mixed oxide and chalcocite ores, notably in Chile. Currently, there are significant development efforts underway to try to extend heap leaching to chalcopy-rite ores. 

Fig. 18 General flowsheet of copper leaching, solvent extraction, and electrowinning process. 

Direct treatment of oxide, silicate and carbonate zinc ores is difficult if conventional zinc technology is used (leaching, purification by means of cementation with zinc powder and zinc electrowinning). There is only one case (Padaeng, Thailand) where conventional zinc flowsheets were successfully modified to treat zinc silicate ores. This was possible given the high-grade zinc ore treated (30% Zn) and the fact that this plant was able to solve Ae solid-liquid separation problems. 

Figure 1. A flowsheet for recovering nickel from industrial waste streams by solution purification and electrowinning. 

Copper refinery bleed streams contain various amounts of nickel mixed with copper, iron, arsenic and other impurities. Separation of the impurities is achieved by pH adjustment to precipitate the impurities. A nickel carbonate intermediate product can be produced to feed the EMEW circuit and control pH during electrowinning. A schematic diagram showing a basic flowsheet for processing crude nickel sulfate from copper refinery bleed is provided in Figure 2. In cases where the bleed from the copper refinery is processed directly by an acid purification unit [10, 11], the return of acid to the refinery is accomplished and the cost of neutralization is significantly reduced. 

The PLATSOL M treatment of a nickel rich concentrate and a pyrrhotite 3 cleaner concentrate was demonstrated. The PLATSOL autoclave process was combined with precious metal precipitation, copper concentrate enrichment, copper removal, iron/aluminum removal, mixed hydroxide precipitation of nickel and cobalt and finally magnesium removal. The copper concentrate enrichment process proved to be a novel addition to the NorthMet flowsheet. The copper in solution from the autoclave processing was recovered by metathesis on the copper concentrate in the enrichment process. The solvent extraction and electrowinning of copper process applied to precious metal free PLATSOL solutions is no longer required by using this metathesis process route. This development provides maximum operational flexibility for treatment of the NorthMet ore. 

From such a concentrated aqueous solution of the metal, the recovery of the metal is achieved in a variety of the ways. The metal may be precipitated as a hydroxide, an oxide, or calcined as an oxide or recovered as a metal via electrowinning (e.g., Cu, Co, Ni), etc. Illustrations of process flowsheets for the recovery of a variety of metals, e.g. copper, zinc, nickel, uranium, chromium, beryllium, etc., are available in Ritcey and Ashbrook (1984b). Benedict et al. (1981) also provide process flowsheets and descriptions of metals relevant to the nuclear power industry. 

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