The structural characteristic and surface physicochemical properties of bagasse magnesium lignosulfonate(MLS) are investigated by means of GPC

UV

IR and 13C NMR. Four purified MLS fractions with different molecular weights were obtained by fractionation using ultrafiltration and analyzed. The results show that MLS contained more syringin phenyl propane

and less guaiacol phenyl propane comparing with woody calcium lignosulfonate (CLS). The average molecular weight of MLS and the content of sulfonic and phenolic hydroxyl group are lower than that of CLS. As the increasing of molecular weight of MLS

the mass fraction of sulfonic and phenolic hydroxyl group increases. The relative molecular weight distribution and the content of sulfonic and phenolic hydroxyl group are the main affecting factors on the adsorption characteristic of MLS on cement-water interface and the surface charge of cement particle absorbing MLS. With the increasing of molecular weight of MLS

the Zeta potential absolute value of cement particle increases. The adsorbing amount and the Zeta potential absolute value of the surface of cement particle adsorbing MLS fraction with the molecular weight more than 50000

is similar to that of CLS

and its adsorption isotherm follows Langmuir type.