sulfaattimenetelmänä

Sulfaattimenetelmänä, often referred to as the sulfate process, is a method used in industrial chemistry, particularly in the production of pulp and paper. This process involves the chemical recovery of pulping chemicals. In the context of the Kraft process for producing wood pulp, the sulfate method is crucial for regenerating the cooking chemicals, primarily sodium hydroxide and sodium sulfide, from the spent cooking liquor, known as black liquor.

The black liquor, a byproduct of wood pulping, contains dissolved lignin and the inorganic pulping chemicals. The sulfate method involves concentrating the black liquor through evaporation. This concentrated liquor is then burned in a recovery boiler. This combustion serves two main purposes: it generates heat and steam for the mill, and it converts the inorganic compounds into a molten smelt. The smelt, primarily composed of sodium carbonate and sodium sulfide, is then dissolved in water to form green liquor.

The green liquor is further processed in a causticizing process, where calcium hydroxide is added. This reaction converts sodium carbonate into sodium hydroxide, regenerating the primary cooking chemical. The calcium carbonate, or lime mud, precipitates out and is then calcined in a lime kiln to regenerate calcium hydroxide, allowing for its reuse. The sulfate method is vital for the economic viability and environmental sustainability of modern pulp mills, as it minimizes the need for fresh chemical inputs and reduces waste.