Removal of divalent cations and oxyanions by keratin-derived sorbents: Influence of process parameters and mechanistic studies

Irum Zahara, Muhammad Faisal Irfan, Muhammad Zubair, Tariq Siddique, Aman Ullah, Removal of divalent cations and oxyanions by keratin-derived sorbents: Influence of process parameters and mechanistic studies, Science of The Total Environment, Volume 891, 2023, 164288, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2023.164288.

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Currently, water pollution is a significant threat to human health and the environment around the globe. Industrial wastewater most commonly contains heavy metals (Ni, Zn, Cd, Hg, Pb, As, Cu, Cr, Co, Fe, Mn) along with other metals (Ca, Sb, Ag, B, Mo) which are considered to be hazardous, non-biodegradable, carcinogenic, and have a high affinity to assemble in the food chain and human body. So, it is essential to remove heavy metals from water resources, even if detected in trace amounts, to secure a healthy environment. Keratin proteins are one of the sustainable and renewable biomass resources that have the potential to be utilized as an adsorption material for the heavy metals remediation. Chicken feathers (CFs) are by-products produced in large quantities by the poultry industry and they contain >90 % of keratin protein. By modification with chemical agents, the adsorption capacity of the CF keratin can be improved. In our previous study, we reported the influence of chemical modification of CFs keratin with eight different chemical agents. Herein, we studied three out of the eight available KBPs (KBP-I, KBP-IV, KBP-V) adsorbents based on preliminary screening of their adsorption performances. So, the main objective is to investigate the processing parameters, i.e., temperature, contact time and pH, adsorption equilibria and mechanistic behavior related to the adsorption of divalent cations and oxyanions.

Approach

Chicken/keratin feathers (KBP–I) were washed, dried, ground and processed to prepare KBP-IV, KBP-V, and KBP-VII. The KBP-IV was prepared by the chemical modification of processed CFs using the ionic liquid [1-butyl-3-methylimidazolium bromide (BMIM)Br]. The KBP-V was prepared from processed CFs by a method already reported by Zahara et al., 2021. The KBP-VII was modified using the mercaptopropylisobutyl- polyhedral oligomeric silsesquioxanes (POSS). Removal of metal ions were tested under the influence of process parameters (temperature, contact time, and pH of the aqueous solution). Then, the adsorption mechanisms involved in the removal of divalent cations and oxyanions from synthetic wastewater by KBP-IV and KBP-V was investigated.

Analysis of Results

The KBPs provide an optimization of the adsorption parameters (temperature, contact time, and pH) based on their better metal adsorption abilities owing to the larger accessibility of functional groups present on the surfaces. The incubations of KBP-I, KBP-IV, and KBP-V at 30 °C and 45 °C with MMSW, elaborated that 30 °C is the optimized temperature for the removal of divalent cations and oxyanions using the KBP-I and KBP-IV. However, KBP-V adsorbed divalent cations effectively at 45 °C. For divalent cations and oxyanions adsorption, the fastest equilibrium was achieved within 15–60 min by KBP-I, KBP-IV, and KBP-V. No significant differences were observed for inorganics removal from MMSW at two initial solution pHs (5.5 and 8.5). However, the divalent cations and oxyanions removal from single metal synthetic wastewater at two pHs (5.5 and 8.5) concluded that KBP-V adsorbed divalent cations at pH 8.5 and KBP-IV removed oxyanions at pH 5.5 effectively. The results of the XPS analysis demonstrated that adsorption mechanisms (complexation/chelation, electrostatic attraction, or chemical reduction) are involved in the removal of divalent cations and oxyanions by KBPs from synthetic wastewater. The adsorption behavior for (Cd2+, Ni2+, CrVI) by using KBP-I, KBP-IV, KBP-V was best described by the Langmuir model, and for AsIII by KBP-I was best described by the Freundlich model. The maximum adsorption capacities were found to be 2.4 mg g−1 for Cd2+, 2.8 mg g−1 for CrVI, and 2.2 mg g−1 for Ni2+ which were comparable with the values reported in the literature for other forms of materials.

Application

The high performance of KBPs towards the inorganic removal (Ba2+ and Sr2+) from field-collected wastewater (OSPW) indicated that developed KBPs display great potential to be utilized as an alternative, cheap and effective material for large-scale industrial wastewater remediation to safe the eco-environment.

Abstract

Keratin has become a promising adsorbing material for the removal of heavy metals from polluted water due to its environmentally benign nature, unique chemical structure, and binding ability. We developed keratin biopolymers (KBP-I, KBP-IV, KBP-V) using chicken feathers, and assessed their adsorption performance against metal-containing synthetic wastewater at varying temperatures, contact times, and pH. Initially, a multi-metal synthetic wastewater (MMSW) containing cations (Cd2+, Co2+, Ni2+) and oxyanions (CrVI, AsIII, VV) was incubated with each KBP under different sets of conditions. Temperature results exhibited that KBP-I, KBP-IV and KBP-V showed higher metals adsorption at 30 °C and 45 °C, respectively. However, the adsorption equilibrium was achieved for selective metals within 1 h of incubation time for all KBPs. For pH, no significant difference was observed in adsorption in MMSW due to buffering of pH by KBPs. To minimize buffering, KBP-IV and KBP-V were tested further for single-metal synthetic wastewater at two different pHs i.e. 5.5 and 8.5. KBP-IV and KBP-V were selected due to their buffering capacities and high adsorption abilities for oxyanions (pH 5.5) and divalent cations (pH 8.5), respectively indicating that chemical modifications changed and enhanced the functional groups of the keratin. X-ray Photoelectron Spectroscopy analysis was performed to demonstrate the adsorption mechanism (complexation/chelation, electrostatic attraction, or chemical reduction) for the removal of divalent cations and oxyanions by KBPs from MMSW. Furthermore, KBPs exhibited adsorption behavior for Ni2+ (qm = 2.2 mg g−1), Cd2+ (qm = 2.4 mg g−1), and CrVI (qm = 2.8 mg g−1) best described by Langmuir model with the coefficient of determination (R2) values >0.95 while AsIII (KF = 6.4 L/g) was fitted well to the Freundlich model with R2 value >0.98. Based on these findings, we anticipate that keratin adsorbents have the potential to employ at a large scale for water remediation.