Magnesium oxide (chemical formula: MgO; relative molecular mass: 40.30), commonly known as "bitter earth" or "lamp powder," is an inorganic oxide compound. At room temperature, it appears as a white powder with a density of approximately 3.58 g/cm³, a melting point of 2852°C, and a boiling point of 3600°C; it is sparingly soluble in water and ethanol but soluble in ammonium salt solutions. At high temperatures, magnesium oxide can be reduced to metallic magnesium by strong reducing elements or alloys and reacts with chlorine gas to form magnesium chloride. It reacts with acids to produce the corresponding magnesium salts and water; it releases ammonia when reacting with ammonium salts and forms magnesium carbonate or magnesium sulfate when reacting with acidic oxides such as carbon dioxide or sulfur trioxide, respectively.
Magnesium oxide is primarily produced via three types of processes: first, by calcining, slaking, and carbonating dolomite to obtain basic magnesium carbonate, followed by thermal decomposition, calcination, pulverization, and air classification; second, by removing impurities from the mother liquor remaining after seawater salt production (containing magnesium ions at a mass concentration of approximately 50 g/L), mixing it with ammonium bicarbonate in appropriate proportions for a precipitation reaction, and subsequently performing centrifugal dehydration, drying, calcination, and pulverization; and third, by reacting bittern (concentrated brine) with sodium carbonate to produce heavy magnesium carbonate, followed by roasting and pulverization. Industrially, it serves as a refractory material for ceramics, glass, and metallurgical furnace linings; in environmental engineering, it is used for treating acidic wastewater and desulfurizing flue gas; in the medical field, it acts as an antacid to relieve excess gastric acid; additionally, it is used as a rubber accelerator, an insulating coating for silicon steel sheets, and a feed additive.
Magnesium oxide causes mild irritation to the conjunctiva and nasal mucosa; inhalation of its dust can lead to respiratory difficulties, chest pain, coughing, and diffuse interstitial pulmonary fibrosis complicated by emphysema.