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Treatment of wet nickel smelting (cobalt)-cobalt solution
It belongs to renewable sources of raw materials are cobalt super alloy containing Co50 ~ 60% and of Ni10 ~ 30%, the magnetic alloy containing the Co8 ~ 24 containing Co5 ~ 12% of the high-speed cutting alloys, catalysts for the petrochemical industry as well as other Scraps with high cobalt content, etc. Not long ago, foreign countries also believed that the production of cobalt in recycled raw materials was unprofitable. Later, this view changed. As early as 1979, nearly 2,000 tons of cobalt were produced from recycled raw materials.
The American example is the best sign in this regard. The United States is the basic user of cobalt consumption. In 1980, the country consumed 7,260 tons of cobalt, of which 544 tons were produced from recycled materials.
In the (former) Soviet Union, cobalt- nickel scrap was processed in a modern nickel enterprise by hydrometallurgical methods.
Treatment of cobalt solution
The cobalt sulfide solution is the raw material of the nickel metallurgical workshop of the nickel enterprise. This solution contains (g/dm 3 ): Co 3 to 50 (the Ni content is approximately in this range), Fe 3 to 20, and Cu 0.2 to 0.5. The regenerated cobalt-containing scrap is also dissolved in the sulfuric acid solution. In the filtered solution, the concentration of each metal is similar to the above concentration, depending on the metal content in the raw material.
After the sulfuric acid solution is cleaned, it is precipitated as a hydroxide.
The pH equilibrium values ​​for the formation of certain hydroxides are listed in Table 1.
Table 1 pH equilibrium values ​​of metal hydroxides provided by different authors' data
Compound
Britton
Fearakov
Hefitz and Luo Jingyang
Co(OH)3
Fe(OH)3
Cu(OH)2
Co(OH)2
Fe(OH)2
Ni(OH)2
-
2.0
5.3
6.8
5.5
6.7
-
1.63
4.4
6.78
5.62
6.7
0.9
2.6
4.5
6.4
6.7
7.1
According to the data in Table 1, the precipitation of high-priced metals from solution is much simpler than that of low-priced metals. This principle is widely used in hydrometallurgy. The oxidizing agent can be in a solid state, a liquid state, and a gaseous state. It is important that the oxidation potential of the oxidant is higher than the redox potential of the metal ions in the solution. The redox potential can be calculated as follows:
φ Me 3 + / Me 2+ =φ° Me 3 + / Me 2+ +
RT
Ln
a Me 3 +
(1)
Nf
a Me 2 +
Where, a Me 3 + ---- oxidation ion activity; a Me 2 + ---- reduction ion activity; φ ° Me 3 + / Me 2+ ----25 ° C temperature standard electrode Potential.
Table 2 Electrode potential of redox reaction
reaction
Ion activity in the reaction
medium
Potential (volt)
Co 3 + eâ†â†’Co 2 +
Aco 3 + = aco 2 + =1
-
+1.84
NiO 2 +4H + +2eâ†â†’Ni 2 + +2H 2 O
-
-
+1.77
HClO+H + +eâ†â†’Cl - +H 2 O
-
Acidic
+1.49
1/2 Cl 2 â†â†’Cl -
Acl-=1
-
+1.35
O 2 +4H + +4eâ†â†’H 2 O
a H + =1
-
+1.23
ClO - +H 2 O+2eâ†â†’Cl - +2OH -
Aclo - =1, ao H - =1
Alkaline
+0.94
Fe 3 + + eâ†â†’Fe2+
a Fe 3 + = 3.8 × 10 -8
Acidic
+0.771
Fe 2 + +3OH+â†â†’Fe(OH) 3
a Fe 2 + = 4 × 10 -4
pH=2.5
+0.44
The electrode potentials of some redox reactions are listed in Table 2. As can be seen from the data in Table 2, the effect of oxygen is to oxidize Fe 2 + to Fe 3 + . In order to make cobalt, nickel and manganese into high valence, it is necessary to use a stronger oxidizing agent, such as gaseous chlorine or hypochlorite, and the medium should be acidic.
The hydrolysis of the hydroxide is stepwise precipitated, and the reaction is as follows:
2FeSO 4 +3Na 2 CO 3 +6H 2 O=2Fe(OH) 3 +2NaCl+3Na 2 CO 3 +2Na 2 CO 3 (2)
When the pH is 4.0 to 4.5 (solubility Fe(OH) 2 = 4 × 10 -38 ), the insoluble hydroxide of iron is actually produced simultaneously:
2CuSO 4 +2Na 2 CO 3 +2H 2 O=CuCO 3 ·Cu(OH) 2 +Na 2 SO 4 +H 2 CO 3 (3)
The pH of the basic carbonate precipitation of copper is 5.5.
2CoSO 4 +Cl 2 +3Na 2 CO 3 +6H 2 O=2Co(OH) 3 +2NaCl+2Na 2 SO 4 +3H 2 CO 3 (4)
pH precipitation = 3.0 to 3.5, solubility product Co(OH) 3 = 2.5 × 10 -43
2MnSO 4 +2Cl 2 +4Na 2 CO 3 +4H 2 O=2Mn(OH) 4 +2Na 2 SO 4 +4NaCl+4CO 2 (5)
Mn(OH) 4 r pH precipitation = 2.5. Manganese is the most difficult impurity to exclude.
In order to correctly evaluate the step-by-step removal of impurities from the solution, not only thermodynamic data but also the kinetics of hydroxide formation are required.
The precipitation can be carried out in a Paqueck leaching tank (with compressed air agitation) or in a device with mechanical agitation, with a pore filter for solid-liquid separation.