Reductive roasting is at a temperature below the melting point of the charge and reducing atmospheric conditions, so that the metal oxide ore is converted to the corresponding process low valent metal oxide or metal. The reduction of metal oxides can be expressed by the following formula:
MO+R ==== M+RO
Where MO - metal oxide;
R, RO - reducing agent and reducing agent oxide.
Any substance having a chemical affinity for oxygen that is greater than the affinity of the reduced metal to oxygen can be used as a reducing agent for the metal oxide. At higher temperatures, carbon can act as a reducing agent for many metal oxides, and the reducing agents commonly used in production are solid carbon, carbon monoxide gas, and hydrogen.
Reductive calcination is currently mainly used to treat difficult mineral materials such as iron , manganese , nickel , copper , tin and antimony . It is also used in concentrates to remove impurities and coarse concentrates.
For example: reduction roasting of nickel-containing laterite ore. Nickel-containing laterite ore is the world's largest nickel oxide ore resource. Due to its low grade, nickel is chemically impregnated and cannot be enriched by physical beneficiation . The recovery of nickel therefrom by reduction roasting-low pressure ammonia leaching has been industrially applied. The nickel oxide is previously reduced to active metal nickel, a nickel alloy is drilled, and then nickel is recovered by ammonia leaching.
The oxygen is selectively subjected to selective reduction roasting with a gas reducing agent (CO-CO 2 , H 2 -H 2 O), and the main reaction is as follows:
NiO+H 2 0 ==== Ni+H 2 O
NiO+CO ==== Ni+CO 2
CoO+H 2 ==== Co+H 2 O
CoO+CO ==== Co+CO 2
3Fe 2 s3 +H 2 ==== 2Fe 3 O 4 +H 2 0
3Fe 2 0 3 +CO ==== 2Fe 3 O 4 +CO 2
Fe 3 O 4 +H 2 ==== 3Fe0+H 2 0
Fe 3 O 4 +CO ==== 3Fe0+CO 2
FeO+H 2 ===== Fe+H 2 O
FeO+CO ==== Fe+CO 2
H 2 0+CO ==== H 2 +CO 2
CO 2 +C ==== 2CO
If the controlled gas phase composition CO 2 /CO is greater than 2.53 or H 2 0/H 2 is greater than 2.45, the nickel diamond oxide can be preferentially reduced to metallic nickel and diamond, and most of the iron oxide is reduced to magnesite without generating metallic iron. However, since the bonding state of the metal oxide in the ore is complicated and the reaction speed is increased, the gas phase composition ratio should be smaller. When the gas phase composition is controlled at CO 2 :CO = 1:1, a small amount of ferrous oxide and metallic iron are inevitably formed.
The reduction of roasting nickel-containing laterite ore is generally carried out by multi-layer roasting protection in foreign countries, and a rotary kiln can also be used.
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