Industrial lignins: the potential for efficient removal of Cr(VI) from wastewater

Abstract

Cr(VI), a serious threat to human health, widely exists in the effluents of various industrial processes.. In this paper, the potential of industrial lignin for efficient removal of Cr(VI) from wastewater were systematacially investigated, including pulping black liquor lignin (BLN), enzymolysis lignin (ELN), and SPORL pretreatment spent liquor (FS). The structure characterizations of three lignins were investigated by TG, FTIR, BET, SEM, and XPS. Among these three lignins, BLN showed the highest adsorption amount of Cr(VI) and best selectivity in wastewater simulation. According to the Langmuir model, the calculated maximum adsorption amount of Cr(VI) on ELN, BLN, and FS was 765.60, 880.57, and 721.58 mg g -1 , respectively. The adsorption of Cr(VI) by industrial lignins was a chemisorption process, during which Cr(VI) was reduced to low toxic Cr(III). This paper provided a promising application for the effective utilization of industrial lignins.

Valorisation of Lignocellulosic Wastes, the Case Study of Eucalypt Stumps Lignin as Bioadsorbent for the Removal of Cr(VI)

“…The extremely high values of R 2 for the pseudo-second-order model for both adsorbents (0.9995 and 0.9951) indicate that the limiting factor of the adsorption rate of Cr(VI) ions could be chemisorption, since the other two models provided a comparatively poorer fit. Similar behaviour was reported by Zhang and Zhou [ 15 ], testing industrial lignins as adsorbents for Cr(VI) and attained R 2 > 0.995 for the pseudo-second-order model. Furthermore, the value of the pseudo-second-order rate constant, k 2 , for eucalypt lignin is significantly higher, implying faster adsorption (0.00835 g/mg min), as previously discussed.…”

“…After 360 min, about 86% of the total initial number of ions was adsorbed, which is a significant advantage in terms of its practical application in water treatment: with the reduction in contact time, the operational costs of the process would also reduce, although the use of eucalypt stump lignin compared with kraft lignin would provide a lower residual concentration. Other industrial lignins (e.g., pulping black liquor) revealed a long time (4320 min) to reach the adsorption equilibrium [ 15 , 16 ].…”

“…In contrast, the Freundlich and Dubinin–Radushkevich models provided poor fitting (R 2 of 0.8642 and 0.9141, respectively). Fitting by the Langmuir model resulted in a slightly higher R 2 (0.9979), indicating that the surface of this type of lignin is homogenous, with a fixed number of identical active sites for Cr(VI) ions [ 15 ]. Furthermore, the value obtained from the equation for the maximum adsorption capacity, q m , was 256.4 mg/g, which is approximate to the experimentally obtained value (251.3 mg/g, Figure 7 a).…”

“…In addition, a decrease in the intensity of the bands between 1600 to 1000 cm −1 was observed, meaning that functional groups such as the methoxyl groups (OCH 3 ), which have a band of 1462 cm −1 , may participate in the adsorption of Cr(VI), as also mentioned in literature [ 41 , 42 , 43 ]. More recently, Zhang and Zhou [ 15 ] also refer to a disappearance of the bands related to CH stretching, phenolic OH, CO stretching, and carbonyl groups in the lignins after the adsorption of Cr(VI).…”

“…Lignin presents a significant advantage in water treatment as it does not impose environmental issues, due to its insolubility in water and because it is entirely biodegradable. The possibility of metal recovery from lignin by acidification is followed by precipitation [ 10 ], and heavy metal adsorption onto lignins of various origins has been documented in the literature [ 1 , 11 , 12 , 13 , 14 , 15 ]. More recently, lignin modifications have been made to improve its adsorption capacity [ 16 , 17 ].…”