Trivalent chromium and hexavalent chromium are the two common valence states of chromium, and they differ significantly in their properties, applications, and environmental impacts:
Author: Anna
Trivalent chromium and hexavalent chromium are the two common valence states of chromium, and they differ significantly in their properties, applications, and environmental impacts:
Toxicity and Environmental Impact:
Trivalent chromium (Cr³⁺): is relatively non-toxic and has a low environmental impact. It is relatively common in nature, and some forms of trivalent chromium (e.g., chromium complexes in some nutritional supplements) have additional benefits for the human body, such as involvement in glucose metabolism.
Hexavalent chromium (Cr⁶⁺): highly toxic, highly hazardous to the environment and human health, and classified as a carcinogen. Hexavalent chromium easily penetrates cell membranes, causing DNA damage and triggering hereditary genetic defects. Long-term exposure may cause inflammation of the respiratory tract, allergic dermatitis, and even increase the risk of lung cancer. In the environment, hexavalent chromium contamination is persistent and requires specialized methods for treatment.
Redox properties:
Trivalent chromium is in the reduced state, meaning it can be further oxidized, while hexavalent chromium is in the oxidized state and can be reduced. In electrochemical reactions, trivalent chromium can be oxidized to hexavalent chromium and vice versa.
Applications:
Trivalent chromium is not as widely used in electroplating as hexavalent chromium, which has a lower hardness of the plated layer, but is less polluting to the environment and is gradually being developed as a more environmentally friendly alternative.
Due to its high corrosion resistance and self-healing ability, hexavalent chromium was once widely used in electroplating, passivation processes, and as a colorant in pigmentation, providing excellent rust protection and rich color effects. However, given its high toxicity, many applications have turned to safer alternatives.
Treatment Methods:
Treatment of hexavalent chromium usually requires special chemical or biological methods, such as adsorption of biomaterials, to remove hexavalent chromium from water or waste streams and reduce environmental pollution.
In summary, trivalent chromium and hexavalent chromium are significantly different in terms of toxicity, environmental friendliness, range of applications, and treatment methods, where hexavalent chromium is facing strict restrictions on its use due to its high toxicity, whereas trivalent chromium is regarded as a safer option, although the technology of its application in some areas is still under development.