Sherritt Gordon process

Another important example is the leaching of nickel sulfide under ammonia and oxygen pressure to form hexaammine nickel (Sherritt-Gordon process). 

The removal of copper from the pregnant nickel solution in the Sherritt-Gordon process is an example of purification by precipitation of a fairly insoluble compound. First, in the copper boil step, ammonia is driven off by heating the solution, and some copper sulfide precipitates. The residual copper is removed by a dding hydrogen sulfide for the chemical precipitation of mote copper sulfide. 

Gas Reduction. The use of a gaseous reduciag agent is attractive because the metal is produced as a powder that can easily be separated from the solution. Carbon dioxide, sulfur dioxide, and hydrogen can be used to precipitate copper, nickel, and cobalt, but only hydrogen reduction is appHed on an iadustrial scale. In the Sherritt-Gordon process, the excess ammonia is removed duting the purification to achieve a 2 1 ratio of NH iNi ia solution. Nickel powder is then precipitated by... 

Figure 5.9 Sherritt-Gordon process of nickel production.

Another Sherritt-Gordon process is for leaching zinc from sulfide ores, again using oxygen under pressure. 

Low-molecular-weight extractants can generally be expected to have uneconomic solubilities in most systems, but where high salt concentrations prevail, the solubility may be substantially lower and may be economic. This has been shown to be true for naphthenic and Versatic acids, which have high solubilities in water but appear to be economically useful when used in high ammonium sulfate liquors, such as those produced in the Sherritt-Gordon process for the extraction of cobalt and separation from nickel [12]. 

Metals such as copper, nickel, and cobalt can be precipitated from aqueous solutions by hydrogen reduction. However this requires buffering (ammo-niacal solutions are used in the classical Sherritt-Gordon process) and high hydrogen pressures, which would be difficult to attain for most environmental applications. ... 

Figure 9.3-S is a Pouibaix. predominant-area, diagram for the S-O-H2O system for a total activity of all dissolved sulfur species of 10" (ES = 10" ). The only stable sulfur species are HSO4, SC ". H2S, HS", and elemental sulfur. The formation of elemental sulfur films occurs in acid solutions as indicated. In basic solution, during the oxidation of sulfiir-bearing compounds, intermediate metastable sulfur species such as thiosulfate, dithionate, and polythionates form. This is a problem previously described in the Sherritt Gordon process. Under acid conditions, during the dissolution of sulfide minerals, elemental sulfur layers often form but metastable sulfur intermediates such as thiosulfate and sulfite are not observed.

---