Silica conjugated with kraft lignin and its use as a novel ‘green’ sorbent for hazardous metal ions removal

• Silica/lignin hybrid material with defined surface and physicochemical properties were developed.
• Advanced silica/lignin material as a novel ‘green’ sorbent for Ni2+ and Cd2+ ions removal.
• The pseudo second-order and the Langmuir isotherm model were suitable to characterize the process of adsorption.

An advanced functional silica/lignin material was obtained and tested as a novel adsorbent of nickel(II) and cadmium(II) ions. The ‘green’ sorbent was obtained chemically from the commercial silica Syloid®244 and kraft lignin. The resulting hybrid material exhibited specific physicochemical and structural properties, which were determined by a number of methods, including Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy, electrophoretic light scattering, nitrogen sorption and others. The surface area of the hybrid material was 223 m2/g. The obtained material was tested as an adsorbent of hazardous metals from aqueous solutions, and an analysis was made of parameters influencing the effectiveness of the adsorption process, such as duration, pH of solution and mass of adsorbent. The kinetics of the process were approximated by pseudo-first-order and pseudo-second-order models; the experimental data were found to correspond well to the pseudo-second-order model, with correlation coefficient r2 = 0.999. The isotherms of adsorption equilibrium were fitted by the Langmuir and Freundlich models using a nonlinear regression method, and good correspondence of the experimental data to the Langmuir isotherm was obtained.

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