Bioadsorption of trivalent and hexavalent chromium from aqueous solutions by sericin-alginate particles produced from Bombyx mori cocoons

Abstract

In this study, particles produced from sericin-alginate blend were used as non-conventional bioadsorbent for removing Cr(III) and Cr(VI) from aqueous solutions. Besides chromium mitigation, the use of sericin-alginate particles as bioadsorbent aims to offer an environmental solution of added value for sericin, which is a by-product from silk industry. Sericin-alginate particles in natura and loaded with Cr(III) and Cr(VI) were characterized using N₂ physical adsorption analysis, optical microcopy, mercury porosimetry, helium pycnometry, scanning electron microscope coupled with energy dispersive X-ray spectrometer, Fourier transform infrared spectrometer, and X-ray diffraction. Kinetic studies on the removal of Cr(III) (at pH = 3.5) and Cr(VI) (at pH = 2) indicate the ion exchange mechanism with Ca(II) and the predominance of external mass transfer resistance. Cr(VI) uptake occurs through an adsorption-coupled reduction process, and bioadsorption equilibrium is reached after ~ 1000 min. Cr(III) bioadsorption occurs faster (~ 210 min). The Cr(VI) bioadsorption is endothermic, as bioadsorption capacity increases with temperature: 0.0783 mmol/g (20 °C), 0.1960 mmol/g (30 °C), 0.4570 mmol/g (40 °C), and 0.7577 mmol/g (55 °C). The three-parameter isotherm model of Tóth best represents the equilibrium data of total chromium. From Langmuir isotherm model, the maximum bioadsorption capacity is higher for total chromium, 0.25 mmol/g (30 °C), than for trivalent chromium, 0.023 mmol/g (30 °C). The comparison of bioadsorption capacities with different biomaterials confirms sericin-alginate particles as potential bioadsorbent of chromium.