Importance

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Abstract

The invention relates to separation of lignin from an aqueous slurry containing lignocellulosic biomass material, such as black liquor, comprising the steps of providing an aqueous slurry having an initial pH level to a first precipitation phase, where the first precipitation phase is performed during a first time duration including adding a first acidifier. Thereby, a decrease in the pH value of the aqueous slurry from the initial pH level to a first pH level above 11 is created. Thereafter, processed aqueous slurry is fed from the first precipitation phase to a second precipitation phase. The second precipitation phase is performed during a second time duration. The second precipitation phase includes adding of a second acidifier, wherein a decrease in the first pH value from said first pH level to a second pH level above 9 is created.

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First Claim