Investigation of black liquor-derived carbon for removal of Cr(VI): Comparison with lignin-derived carbon

Abstract

In this work, industrial black liquor (BL) was directly used to prepare activated carbons with high surface area and large pore volume through K2CO3 activation. The effect of activation temperature on the properties and the Cr(VI) removal performance of activated carbons were investigated. For comparison, the purified lignin (PL) was also investigated. The specific surface area and the total pore volume of BL derived carbon prepared at 800 °C (CBLS800) were 1335.58 m2/g and 1.79 cm3/g, while those of PL derived carbon prepared at 900 °C (CPL900) were 1715.16 m2/g and 1.12 cm3/g. The Cr(VI) removal process conforms to the pseudo-second-order kinetic model, indicating that the adsorption process is mainly controlled by chemical interaction. The fitting of isotherm was more consistent with Langmuir model. The maximum adsorption amount of Cr(VI) on CBLS800 and CPL900 was 669.70 and 645.73 mg/g at 45 °C and pH 2.0, respectively. The negative ΔG° and positive ΔH° confirmed that the adsorption of Cr(VI) onto CBLS800 and CPL900 was an endothermic and spontaneous process. The removal mechanism of Cr(VI) mainly includes three aspects: intra particle diffusion, electrostatic attraction and adsorption-coupled reduction. This work not only provides a theoretical basis for transforming BL into functionalized biochar materials, but also makes the efficient removal of Cr(VI) from wastewater possible.