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Fantastic changes in metal oxides: Do you know how to extract metals from ores?
Oxides refer to compounds containing at least one oxygen atom and other elements in their chemical formula. The oxide itself is a state of oxygen ions with a net charge of -2. The oxidation state of oxygen in its chemical formula is -2. The Earth's crust is mostly composed of oxides, and even materials considered to be pure elements often form surface films of oxides. For example, aluminum foil will form a thin layer of Al2O3 (called a passivation layer) in an oxidizing environment to protect it from further oxidation.
The formation pathways of oxides are very diverse and are closely related to almost all elements.
The formation process of metal oxides
The production of metal oxides is often accompanied by the decomposition of other metal compounds, such as carbonates, hydroxides and nitrates. Taking the production of calcium oxide as an example, when calcium carbonate (limestone) is heated and decomposed, carbon dioxide is released:
CaCO3 → CaO + CO2
In an oxygen atmosphere, almost all elements will react with oxygen when heated, resulting in an oxidation reaction. For example, zinc powder burns in the air to produce zinc oxide:
2 Zn + O2 → 2 ZnO
In the process of refining metals from ores, oxides are often generated by roasting metal sulfide ores. Taking molybdenum ore (MoS2) as an example, it is transformed into molybdenum trioxide after roasting, which is the precursor of almost all molybdenum compounds:
2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2
Precious metals such as gold and platinum are prized for their resistance to direct chemical binding with oxygen.
Diversity of non-metal oxides
Among the non-metal oxides, the most important and common include carbon dioxide and carbon monoxide. The formation of these substances results from the complete or partial oxidation of carbon or hydrocarbons. In the absence of oxygen, carbon monoxide is produced:
CH4 + 3/2 O2 → CO + 2 H2O
In an environment with excess oxygen, carbon dioxide is produced:
CH4 + 2 O2 → CO2 + 2 H2O
It is relatively difficult to convert nitrogen into oxides, but the combustion of ammonia can generate nitric oxide, which further reacts with oxygen to form nitrogen dioxide.
Structures and reactions of oxides
The structures of oxides range from individual molecules to polymeric and crystalline structures. Solid oxides usually have the structure of polymers, and while most metal oxides are crystalline solids, many non-metal oxides are molecules. Examples of molecular oxides include carbon dioxide and carbon monoxide.
The reduction reaction of oxides is widely used in the production of certain metals. Many metal oxides can be reduced to metals by heating. Take silver oxide as an example, it decomposes at 200°C:
2 Ag2O → 4 Ag + O2
Most commonly, metal oxides are reduced by reaction with chemical reagents. A commonly used reducing agent is carbon in the form of coke. For example, the smelting process of iron ore involves multiple reactions, and the simplified equation is as follows:
2 Fe2O3 + 3 C → 4 Fe + 3 CO2
Dissolution of oxides often improves metal recovery and utilization.
With the deepening of scientific research, our understanding of oxides is also increasing. This is not only important for materials science, but also plays an important role in fields such as catalysis, energy storage and environmental governance. As our knowledge of metal oxides deepens, what new technologies can we use this information to pursue?
