Lead adsorption by silica-immobilized humin under flow and batch conditions: assessment of flow rate and calcium and magnesium interference

Roles of different humin and heavy-metal resistant bacteria from composting on heavy metal removal

This study aims to assess the roles of different humin and heavy-metal resistant bacterial community from composting on heavy metal removal. The results showed that the concentration of Cu²⁺, Zn²⁺, Ni²⁺, Pb²⁺, Cr³⁺ and Cd²⁺ decreased with adding the compost-derived humin, but the removal rates were relatively low (<30% on average). The heavy metal resistant bacteria from composting have better metal binding capacities than humin, and the combined addition of humin and bacteria could further stimulate the biosorption of heavy metals with 60-80% removal of metals and improve the diversity and biomass of bacterial community. There was obviously increased synergy between the humin from maturity phase and bacteria for metal biosorption ("1 + 1 > 2"). Structural equation modeling showed that microbial biomass and humin humification are the key factors for the biosorption of heavy metals. Combining humin from maturity phase with heavy-metal resistant bacteria was suggested to control heavy metal pollution in composts.

Polyphenol-SiO2 hybrid biosorbent for heavy metal removal. Yerba mate waste (Ilex paraguariensis) as polyphenol source: kinetics and isotherm studies

A low-cost biosorbent hybrid material ready for application was obtained in this work. Yerba mate (Ilex paraguariensis) milling residual dust was used as a polyphenol source by ethanolic extraction. Polyphenols were immobilized within a SiO(2) matrix to form an interpenetrated polymer after glutaraldehyde cross-linking. Pb(II), Cr(III) and Cr(VI) were chosen as model metals for adsorption. The hybrid materials were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and Nitrogen Adsorption Isotherms. Adsorption experimental data were analysed using Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Redlich-Peterson, Sips and Toth isotherm models along with the evaluation of adsorption energy and standard free energy (ΔG°). The adsorption was observed to be pH dependent. The main mechanism of metal adsorption was found to be a spontaneous charge associated interaction. Electron Spin Resonance (ESR) spectroscopy confirmed that Cr(VI) adsorption was an adsorption-coupled reaction and the adsorbed specie was Cr(V). The hybrid matrix probed its adsorption capacity of Cr(III) in a non-treated tannery wastewater.

Removal of dyes from water using chitosan hydrogel/SiO2 and chitin hydrogel/SiO2 hybrid materials obtained by the sol-gel method

This work describes the synthesis of chitosan hydrogel/SiO(2) and chitin hydrogel/SiO(2) hybrid mesoporous materials obtained by the sol-gel method for their use as biosorbents. Their adsorption capabilities against four dyes (Remazol Black B, Erythrosine B, Neutral Red and Gentian Violet) were compared in order to evaluate chitin as a plausible replacement for chitosan considering its efficiency and lower cost. Both chitin and chitosan were used in the form of hydrogels. This allowed full compatibility with the ethanol release from tetraethoxysilane. The hybrid materials were characterized by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Nitrogen Adsorption Isotherms and (13)C solid-state Nuclear Magnetic Resonance. Adsorption experimental data were analyzed using Langmuir, Freundlich and Dubinin-Radushkevich isotherm models along with the evaluation of adsorption energy and standard free energy (ΔG(0)). The adsorption was observed to be pH dependent. The main mechanism of dye adsorption was found to be a spontaneous charge associated interaction, except for EB adsorption on chitin/SiO(2) matrix, which showed to involve a lower energy physical adsorption interaction. Aside from highly charged dyes the chitin containing matrix has similar or higher adsorption capacity than the chitosan one.

Sorption of hazardous metals from single and multi-element solutions by saltbush biomass in batch and continuous mode: interference of calcium and magnesium in batch mode

Batch studies were performed to determine the interference of calcium (Ca) and magnesium (Mg) on the sorption of Cu(II), Cd(II), Cr(III), Cr(VI), Pb(II), and Zn(II) [from CuSO(4), K(2)Cr(2)O(7), Pb(NO(3))(2), Cr(NO(3))(3), ZnCl(2), and Cd(NO(3))(2)] by saltbush (Atriplex canescens) biomass. The results demonstrated that Ca and Mg at concentrations of at least 20 times higher than the concentration of most of the target metals did not interfere with the metal binding. The data show that the batch binding capacity from a multimetal solution at pH 5.0 was (micromol/g) about 260 for Cr(III) and Pb, and about 117, 54, and 49 for Cu, Zn, and Cd, respectively. The use of 0.1M HCl allowed the recovery of 85-100% of the bound Cu, Cr(III), and Pb, and more than 37% of the bound Cd and Zn. The column binding capacity for Pb was about 49 micromol/g from both the single and multimetal solutions, while it was, respectively about 35 and 23 micromol/g for Cr(III). The binding capacity for Cu and Zn from the single and multimetal column experiments was 35 micromol/g and less than 10 micromol/g, respectively. The stripping data from the single column experiment showed that 0.1M HCl allowed the recovery of all the bound Cu and Zn, 90% and 74% of the bound Pb and Cr(VI), respectively, and less than 25% of the bound Cd and Cr(III), while the stripping from the multimetal experiment showed that 0.1M HCl allowed the recovery of all the bound Cu and about 74%, 54%, 43%, and 40% of the bound Pb, Zn, Cd, and Cr(III), respectively.