The spent liquor (SL) of a neutral sulfite semichemical pulping process contains lignocelluloses that are currently treated in a waste water system. In this work, an adsorption process using activated carbon (AC) was considered for isolating the lignin and hemicelluloses from SL. The maximum adsorptions of 0.9 g/g lignin and 0.43 g/g of hemicelluloses on AC were achieved under the conditions of 30 degrees C, pH 7 and 3 h with SL/AC weight ratio of 90. The addition of polydiallyldimethylammonium chloride (PDADMAC) to the SL/AC system significantly improved the adsorption of lignin to 2.5 g/g on AC. The molecular weight of PDADMAC considerably affected the results in that the higher MW PDADMAC led to less lignin, but more hemicelluloses, turbidity and chemical oxygen demand removals from the SL. The thermal analysis also revealed that the higher MW PDADMAC generated precipitates with a lower incineration temperature and heating value. (C) 2014 Elsevier Ltd. All rights reserved.