Boosted selectivity and enhanced capacity of As(V) removal from polluted water by triethylenetetramine activated lignin-based adsorbents.

Low-cost natural polymer lignin has been widely used to remove heavy metal ions from polluted water. But it still has some shortcomings, such as poor removal performance, and weak selective adsorption. Thus, in this study, the lignin prepared by Mannich reaction with black liquor was activated with triethylenetetramine (TETA) to achieve a novel adsorbent with high adsorption rates and a strong selectivity for specific oxygen-containing anions. The adsorption capacity of activated lignin (a-CL) on three oxygen-containing anions (i.e. As(V), P(V) and Cr(VI)) was investigated systematically. The adsorption mechanism of a-CL was elucidated theoretically by the density functional theory (DFT) method. Under the same conditions, the selectivity toward oxygen-containing anions by a-CL followed P(V) < Cr(VI) < As(V). Both FT-IR and DFT simulation results revealed that the hydrogen bond between HAsO42- and N dominated the remarkable selectivity of As (V), yielding a maximum adsorption capacity as high as 62.5 mg g-1. Moreover, the adsorption was very fast with a calculated large adsorption kinetic constant. The removal of As(V) reached 100% within 60 min. The As(V) adsorption kinetics and the adsorption isotherms followed the pseudo-second-order and the Langmuir model. This study provides a way for highly selecting removal of As(VI) from polluted water with the lignin.