In the next step, 5000 mL of 0.2 Maluminum potassium sulfate dodecahydrate (AlK(SO4)212H2O) was added quickly to reduce the pH to around 4 with vigorous mechanical stirring at room temperature.
The mixture was then left to stand overnight to ensure the precipitation of lignin in the solution. The precipitate was then observed clearly and it can be easily collected by filtering or centrifugation.
The slurry was carefully washed with DI water several times to eliminate impurities. The powder was finally vacuum-dried for 48 h.