Physico-Chemical Properties Of Black Liquor And The Performance In Mortar

The paper making waste liquor is the main water pollution in China. In the black liquor, alkali lignin accounts for the key ingredient, with non-degraded hemicelluloses, sugars and some mineral salts. Researches indicted that the ingredients in black liquor could help improve the dispersion of cement and delay the cement hydration. That is to say, black liquor could be a potential admixture in cement mortar but there is rarely reported. In this work, the physical and chemical properties of different lignin were studied. The effect of lignin structure on mortar was discovered. In addition, the physical method and Mannich reaction were adopted to modify the black liquor. The products were used as mortar admixture and compared with commercial admixtures to evaluate its feasibility. The conclusions were as follows:Compared with pine alkali lignin, the bagasse alkali lignin has higher lignin content. The structure has higher phenolic hydroxyl group and carboxyl group but lower methoxyl group. The bagasse black liquor also has higher surface activity and foam performance. When used in mortar, the bagasse black liquor reduced the amount of water, the bulk density and the consistency loss after 4h, it also increased the water-retention ratio and the compressive strength of hardened mortar.By single factor test, the effect of admixture on mortar bulk density, water retention, consistency loss, setting time and the compressive strength of hardened mortar were researched. The optimal proportion of modified black liquor product(MBL) was: 75%(w/w) black liquor, 2% defoaming agent, 1% water-reducing agent, 7% thickening agent and 15% setting retarder agent. When the dosage of MBL was 2%, the bulk density was 1850kg/m3, the consisitency loss of 4h was 21.5%, the water-retention ratio was 88.7%, the setting time was 23.76 h and the max compressive strength ratio was 146%. The performance met the standard of JG/T 426-2013 and was superior to commercial mortar admixture.In the Mannich reaction procedure, the effect of formaldehyde and ethidene diamine agent was studied. The results showed that when use 87 g black liquor, 16 g formaldehyde and 10 g ethidene diamine reacted, the amine bagasse black liquor(AGBL) could be an excellent admixture. When the dosage was 0.3%, the amount of water was 280 g, the bulk density was 1788kg/m3, the water-retention ratio was 89.1%, the consistency loss after 4h was 46.7%, so some retarder was needed.The dispersion stability of cement/AGBL was determined. It was the ball bearing effect, the air bubbles and the electric repulsive force that dispersed cement well.