Serine modified lignin flocculant and preparation method thereof

The invention relates to a serine modified lignin flocculant. The preparation method comprises the following two steps: firstly, extracting refined lignin from papermaking black liquor, then dissolving the refined lignin into a sodium hydroxide solution with a certain concentration, fully stirring, then adding a formaldehyde solution and a serine solution, reacting for a certain time at a constant temperature at a proper temperature, after the reaction is finished, acidifying with dilute sulphuric acid with a certain concentration, and centrifugally separating to obtain the lignin. And washing the precipitate with distilled water for several times until the washed distilled water is neutral, and drying under proper conditions to obtain the serine modified lignin flocculant. The flocculant has a good flocculation effect on methylene blue, magenta pigment and metal ions of Cu < 2 + >, Cr < 3 + >, Hg < 2 + > and Pb < 2 + >, when the dosage is 0.5 g/L, the removal rates of the pigments can reach 85% or above, the