Evaluation of the Intrinsic Metal Binding Capacity of Kraft Black Liquor Lignins, 1998 Pulping Conference Proceedings

Current and future environmental performance regulations will necessitate the reduction in the amounts of fresh water employed in the manufacturing of kraft pulps. It is now well appreciated that these changes will lead to an increase in nonprocess elements (NPEs) in various process streams. Perhaps one of the simplest methods of removing NPEs from a kraft mill is by optimizing their association with kraft black liquor lignins. Unfortunately, to date little is known of the fundamental principles contributing to the association of black liquor lignins (BLLs) with NPEs such as Mn, Mg, Ca, Ba, and Fe. This paper examines the relative metal binding capacity of BLLs and the functional groups in lignin that potentially contribute to this effect. A series of conventional and extended modified continuous kraft dissolved lignins were isolated and characterized employing modern NMR techniques. The affinity of BLLs for calcium and barium in a weak sodium hydroxide solution was studied at room temperature. The results of the metal binding studies were then correlated to the functional groups present in lignin.