Preparation of Silk Sericin/Lignin Blend Beads for the Removal of Hexavalent Chromium Ions.

Hyo Won Kwak,Haesung Yun,Ki Hoon Lee,Munju Shin

doi:10.3390/ijms17091466

Hyo Won Kwak, Haesung Yun + Show 2 more

Open Access

https://doi.org/10.3390/ijms17091466

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Abstract

In the present study, novel adsorbents having high adsorption capability and reusability were prepared using agricultural by-products: silk sericin and lignin. Silk sericin and lignin blend beads were successfully prepared using simple coagulation methods for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. A 1 M lithium chloride (LiCl)/dimethyl sulfoxide (DMSO) solvent system successfully dissolved both sericin and lignin and had sufficient viscosity for bead preparation. Compared to the conventional sericin bead adsorbent, sericin/lignin blend beads showed higher Cr(VI) adsorption capacity. The amount of lignin added to the adsorbent greatly affected the adsorption capacity of the beads, and a 50:50 sericin/lignin blend ratio was optimal. Adsorption behavior followed the Freundlich isotherm, which means the adsorption of Cr(VI) occurred on the heterogeneous surface. Cr(VI) adsorption capability increased with temperature because of thermodynamic-kinetic effects. In addition, over 90% of Cr(VI) ions were recovered from the Cr(VI) adsorbed sericin/lignin beads in a 1 M NaOH solution. The adsorption-desorption recycling process was stable for more than seven cycles, and the recycling efficiency was 82%. It is expected that the sericin/lignin beads could be successfully applied in wastewater remediation especially for hazardous Cr(VI) ions in industrial wastewater.

Highlights

Several industrial processes require a variety of heavy metals, and the excessive discharge of heavy metals has been a major environmental problem
The bead-forming capability of the kraft lignin (KL) itself was so poor that a stable spherical shape was not maintained through the coagulation process
silk sericin (SS)/KL beads were prepared based on SS/KL blend ratios ranging from 100:0–30:70

Summary

Introduction

Several industrial processes require a variety of heavy metals, and the excessive discharge of heavy metals has been a major environmental problem. Molecular aggregation and fast gelation occur in sericin/water solutions; this makes the fabrication process difficult to control because of fast variations in viscosity To overcome this solution instability of sericin/water, various alternative solvents to the conventional aqueous systems have been considered, such as formic acid and trifluoroacetic acid [19,20,21,22]. We prepared micro-sized silk sericin particles via an electro-spraying method using this solvent system and investigated the heavy metal removal efficiency of sericin microparticles for wastewater treatment [25,26]. Most studies on the capability of lignin-based pollutant removal investigated the powder or sieve forms of lignin, which are difficult to use in practical pollutant treatment processes These forms of lignin require additional processes, including centrifugation, for the separation of the adsorbent from the pollutant. Models fit to equilibrium isotherms and kinetic data are presented here to validate the usefulness of these novel sericin/lignin beads in heavy metal wastewater treatment

Results and Discussion

Desorption and Regeneration Study

Materials

Batch Adsorption Studies

Desorption and Regeneration Studies

Conclusions