The industrial production of magnesium sulfate typically employs two main processes: the magnesium carbonate process and the magnesium oxide process. The magnesium carbonate process involves crushing magnesite (mainly composed of MgCO₃) and reacting it with sulfuric acid. During the reaction, a large amount of carbon dioxide bubbles are produced, creating a boiling-like phenomenon. Operators must strictly control the reaction temperature between 80-90℃; excessively high temperatures can lead to the formation of the byproduct magnesium pyrosulfate. After the reaction, unreacted slag is removed by vacuum filtration, and the filtrate is concentrated using a triple-effect evaporation system.
The magnesium oxide process uses lightly calcined magnesium oxide powder (MgO) obtained from calcined magnesite as raw material. This powder is neutralized with dilute sulfuric acid in a stirred reactor. This exothermic reaction requires cooling coils to maintain the reaction solution temperature at around 60℃. It is particularly noteworthy that industrial-grade production adds a small amount of hydrogen peroxide as an iron remover, causing iron ions in the solution to precipitate as ferric hydroxide. After plate and frame filtration, the clear magnesium sulfate solution enters the crystallization process.
In the crystallization stage, regardless of the process used, the solution must first be adjusted to a slightly acidic range of 5-6. After concentration to supersaturation using a falling film evaporator, it is introduced into a crystallization tank containing seed crystals. Controlling the cooling rate at 2-3°C per hour yields uniformly sized magnesium sulfate heptahydrate crystals. Modern factories employ fluidized bed drying technology, using 80°C hot air to strictly control the crystal moisture content to below 13.5%. The final automated packaging stage is equipped with a metal detector to ensure that each bag of finished product meets pharmaceutical-grade purity standards (≥99.5%).
In recent years, environmentally friendly production processes have begun to be promoted. For example, using the brine left after potassium extraction from salt lakes as raw material, magnesium sulfate is directly extracted through multi-stage membrane separation technology. This green process not only reduces energy consumption by 30% but also achieves resource recycling. Some high-end production lines are already equipped with DCS control systems, which adjust process parameters in real time using online pH meters and density meters to produce more regular crystal forms, particularly suitable for pharmaceutical excipient requirements.
