Preparation

The copper subgroup metals are mined predominately in native form that influences upon their industrial production.

Copper. The following methods of production are used:

1. Annealing of sulfides

2Cu₂S + 3О₂ = 2Cu₂О + 2SО₂

2Cu₂O + Cu₂S = 6Cu + SО₂.

2. Hydrometallurgical method. To do so the ore is processed by H₂SO₄ or Fe₂(SO₄)₃ solutions and soluble copper sulfate is formed:

(CuOH)₂CO₃ + 2H₂SO₄ = 2CuSO₄ + 3H₂O + CO₂

Cu₂S + 2Fe₂(SO₄)₃ = 2CuSO₄ + 4FeSO₄ + S

The next step is electrodeposition of copper by electrolysis or cementation by Fe powder

Fe + Cu²⁺(aq) → Cu + Fe^{2 +} (aq)

Silver

Silver is mostly produced from polymetallic lead-zinc ores that contain small amounts of silver. Metallic zinc is usually added to molten rough lead. Zinc forms intermetallic compounds with silver Ag₂Zn₃, Ag₂Zn₅ that are insoluble in molten Pb and come to the surface forming “silver foam”. This foam is removed from the surface of molten lead, zinc is distilled off (t_b (Zn) =906°С, t_b (Ag) = 2184°С). Then Ag is purified by electrorefining.

The extraction of silver depends upon the fact that it very readily forms a dicyanoargentate(I) complex, [Ag(CN)₂]^- (linear), and treatment of a silver ore with aqueous cyanide ion CN^- extracts the silver as this complex. The silver is then displaced from the complex by zinc:

2[Ag(CN)₂]^- + Zn = 4CN^- + Zn²⁺ + 2Ag

(Zinc forms only an unstable complex with the cyanide ion.)

Gold extraction .

• Gravity concentration has been historically the most important way of extracting the native metal using pans or washing tables. This method is based on different densities of Au and sand although extraction of gold does not exceed 25%.

• amalgam method (the yield is higher). The comminuted ore is passed over copper leaf covered Hg. Particles of gold that don’t have oxide film are dissolved quickly in Hg. Mercury can be removed from amalgam by distallitation.

• Chemical method. In the presence of air, gold is attacked by sodium cyanide solution, to give the complex dicyanoaurate(I) ion, in which gold has an oxidation state + 1:

4Au + 8NaCN + 2H₂O + O₂ = 4Na[Au(CN)₂] + 4NaOH.

Free gold can be extracted from solution at the presence of zinc:

2Na[Au(CN)₂] + Zn = 2Au + Na₂[Zn(CN)₄]

• Froth flotation is usually applied when the gold present in an ore is closely associated with sulfide minerals such as pyrite or arsenopyrite, and when such sulfides are present in large quantities in the ore. In this case, concentration of the sulfides results in concentration of gold values. Generally, recovery of the gold from the sulfide concentrates requires further processing, usually by roasting or wet pressure oxidation. These pyrometallurgical or hydrometallurgical treatments are themselves usually followed by cyanidation and carbon adsorption techniques for final recovery of the gold.

Electronic Configurations & Oxidation States

Copper subgroup elements are d-elements of IV, V and VI periods that should possess d⁹-electron сonfiguration, although the jump of ns- electron to (n-1)d-sublevel is more energetically favourable:

(n-1)d⁹ns² (n-1)d¹⁰ns¹.

These two states of atoms are close to one another by energy. Therefore, oxidation states +1,+2, and also +3 exist. The latter oxidation state appears when atoms loose 2s electrons and 1 unpaired d-electron.

The most typical oxidation states of Cu are +1, +2, Ag +1, and Au +1, +3 (the most stable are underlined).

The values of atomic radii of these elements are significantly smaller than that of alkali metals belonging to the same group. This fact explains extremely low chemical activity of noble metals of copper subgroup (some authors include only Ag and Au to the noble metals family). Especially low is the reactivity of gold that has equal size to the atom of silver (due to effect of lanthanide contraction) and contain 32 additional electrons simultaneously. The charge of atomic nucleus of gold is larger than silver as well as attraction forces of outermost shell electrons to its own nucleus.

The chemical activity is decreased in the series Cu– Ag — Au.

	Cu	Ag	Au
Rа, nm	0.123	0.144	0.144
radius Е+, nm	0.096	0.116	0.137
	K	Rb	Cs
Rа, nm	0.236	0.248	0.268