Chemical precipitation with sulfide

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Precipitation to form highly insoluble metal sulfides is performed in hydrometallurgical operations in order to recover or remove valuable metals like copper, zinc, nickel and cobalt from process and bleed streams. Common reagents used for precipitation are H2S(g), NaHS and Na2S.

In present applications for heavy metal removal with sulfide, the sulfide needed for precipitation is mostly obtained from chemical sources but sulfide can also be produced biologically

Solubility diagram of metal sulfides. The scale of the x-axis is pS which is defined in the same way as pH where p means the negative logarithm, i.e. a pS of 10 is equal to a sulfide ion concentration of 10-10 M. From the figure it can be seen that metal ions of mercury, silver and copper are most easily precipitated and can be affected at extremely low concentrations of free sulfide ions.
Solubility diagram of metal sulfides. The scale of the x-axis is pS which is defined in the same way as pH where p means the negative logarithm, i.e. a pS of 10 is equal to a sulfide ion concentration of 10-10 M. From the figure it can be seen that metal ions of mercury, silver and copper are most easily precipitated and can be affected at extremely low concentrations of free sulfide ions.

Examples

HS- + Me2+ → MeS + H+ (2)

Me2+ can for example be copper, zinc etc.

See also

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