Manganese is a transition metal. This hard, brittle, silvery-gray metal is the fifth most abundant metal in the Earth’s crust. It is rarely found in its pure metallic form, instead existing in various minerals, most commonly as manganese dioxide (\(\text{MnO}_2\)). The element’s versatility stems from its ability to exist in multiple oxidation states, allowing it to participate in many chemical processes.
Manganese in Steelmaking and Metal Alloys
The largest consumer of manganese worldwide is the steel industry. Manganese’s function in steelmaking is twofold: it acts as a deoxidizer and a desulfurizer. In the molten steel bath, manganese readily reacts with oxygen, forming manganese oxide that floats to the surface as slag and purifies the metal.
Manganese is effective at binding with sulfur, an impurity that causes steel to become brittle. By forming stable, high-melting manganese sulfide particles, the element neutralizes the harmful effects of sulfur. Most manganese is added to steel as ferroalloys, primarily ferromanganese (\(\text{FeMn}\)) and silicomanganese (\(\text{SiMn}\)), which deliver manganese and other purifying agents like silicon.
Beyond its cleansing role, manganese serves as a direct alloying agent that enhances the mechanical properties of the final steel product. The addition of manganese increases the steel’s hardness, tensile strength, and resistance to wear and abrasion. High-manganese steel, sometimes containing over 10% manganese, is known for its exceptional strength and work-hardening capabilities, making it suitable for applications like railway tracks and earth-moving equipment.
Manganese also finds use in non-ferrous metal alloys, notably with aluminum and copper. A small percentage of manganese is introduced to aluminum alloys to increase their strength and corrosion resistance, often used in beverage cans. In copper alloys, it improves the metal’s casting behavior and can be used to create specific alloys with tailored thermal or electrical properties.
Role in Battery Technology and Chemical Production
Manganese compounds are central to industrial applications. Manganese dioxide (\(\text{MnO}_2\)) is the active cathode material in traditional alkaline and zinc-carbon dry-cell batteries, where it undergoes reduction to generate electrical current. In these cells, the \(\text{MnO}_2\) acts as a depolarizer, preventing the buildup of hydrogen gas that would otherwise inhibit battery function.
The element is also gaining importance in the rechargeable battery market, with \(\text{MnO}_2\) used as a cathode material for lithium-ion and aqueous zinc-ion battery chemistries. Electrolytic manganese dioxide (\(\text{EMD}\)), a high-purity form, is manufactured for these high-performance applications. The use of manganese helps improve performance and contributes to a longer battery lifespan.
Potassium permanganate (\(\text{KMnO}_4\)) is valued for its potent oxidizing properties. It is widely used in water treatment facilities to purify drinking water. It effectively oxidizes and removes common impurities such as dissolved iron, manganese, and hydrogen sulfide.
Chemical Synthesis and Disinfectant Use
In industrial chemical synthesis, \(\text{KMnO}_4\) serves as a versatile reagent in the production of complex organic molecules. Its strong oxidative power is harnessed to synthesize compounds used in medicine and food, including ascorbic acid (Vitamin C) and saccharin. This oxidizing ability also makes it a powerful disinfectant, used in industrial cleaning and sanitization protocols, such as those found in pharmaceutical manufacturing and the control of algae in cooling towers.
Manganese compounds are also used to impart color. \(\text{MnO}_2\) was historically used in glassmaking to neutralize the green tint caused by iron impurities, giving the glass a purplish hue.
Manganese as an Essential Trace Nutrient
Manganese is an essential trace mineral for human health. The body contains only about 10 to 20 milligrams of manganese, with the highest concentrations found in the bones, liver, pancreas, and kidneys. Despite the small amount, manganese acts as a cofactor, necessary for the proper functioning of numerous enzymes that drive biological processes.
Manganese superoxide dismutase (\(\text{Mn-SOD}\)) is an enzyme located in the mitochondria that plays a significant role in antioxidant defense by neutralizing harmful free radicals. Other manganese-activated enzymes are directly involved in the metabolism of amino acids, carbohydrates, and cholesterol. For instance, the enzyme arginase requires manganese to function in the urea cycle, which detoxifies ammonia in the liver.
Manganese is integral to the formation of skeletal tissue. It acts as a cofactor for glycosyltransferases, enzymes necessary for the synthesis of proteoglycans. Dietary sources of this trace nutrient include nuts, whole grains, leafy green vegetables, and legumes. A deficiency can impair bone formation and disrupt metabolic and antioxidant pathways.