Practical approach of As(V) adsorption by fabricating biochar with low basicity from FeCl3 and lignin.

One of the main challenges of biochar application for environmental cleanup is rise of pH in water or soil due to high ash and alkali metal contents in the biochar. While this intrinsic property of biochar is advantageous in alleviating soil and water acidity, it severely impairs the affinity of biochar toward anionic contaminants such as arsenic. This study explored a technical approach that can reduce the basicity of lignin-based biochar by utilizing FeCl3 during production of biochar. Three types of biochar were produced by co-pyrolyzing feedstock composed of different combinations of lignin, red mud (RM), and FeCl3, and the produced biochar samples were applied to adsorption of As(V). The biochar samples commonly possessed porous carbon structure embedded with magnetite (Fe3O4) particles. The addition of FeCl3 in the pyrolysis feedstock had a notable effect on reducing basicity of the biochar to yield significantly lower solution pH values than the biochar produced without FeCl3 addition. The extent of As(V) removal was also closely related to the final solution pH and the greatest As(V) removal (>77.6%) was observed for the biochar produced from co-pyrolysis of lignin, RM, and FeCl3. The results of adsorption kinetics and isotherm experiments, along with x-ray spectroscopy (XPS), strongly suggested adsorption of As(V) occurred via specific chemical reaction (chemisorption) between As(V) and Fe-O functional groups on magnetite. Thus, the overall results suggest the use of FeCl3 is a feasible practical approach to control the intrinsic pH of biochar and impart additional functionality that enables effective treatment of As(V).

Adsorption of As(V) and Ni(II) by Fe-Biochar composite fabricated by co-pyrolysis of orange peel and red mud.

This study aimed to compare the adsorption performance of Fe-biochar composites (Fe-C-N2 and Fe-C-CO2), fabricated by co-pyrolysis of red mud and orange peel in N2 and CO2, for As(V) and Ni(II). By the syngas production comparison test, it was confirmed that CO2 was more advantageous than N2 as a pyrolytic medium gas to produce more CO. The resulting Fe-biochar composite showed the aggregate morphology consisting of different Fe phases (magnetite or metal Fe) from the inherent hematite phase in red mud and carbonized carbon matrix, and there was no distinct difference between the structural shapes of two Fe-biochar composites. Adsorption experiments showed that the adsorption capacities for As(V) and Ni(II) in single mode were almost similar with 7.5 and 16.2 mg g-1 for Fe-C-N2 and 5.6 and 15.1 mg g-1 for Fe-C-CO2, respectively. The adsorption ability of Fe-C-CO2 for both As(V) and Ni(II) was further enhanced in binary adsorption mode (As(V): 13.4 mg g-1, Ni(II):17.6 mg g-1) through additional removal of those ions by Ni(II)-As(V) complexation. The overall results demonstrated CO2-assisted pyrolysis can provide a viable platform to convert waste materials into fuel gases and environmental media for co-adsorption of cationic and anionic heavy metals.

Fabrication and environmental applications of multifunctional mixed metal-biochar composites (MMBC) from red mud and lignin wastes.

This study fabricated a new and multifunctional mixed metal-biochar composites (MMBC) using the mixture of two abundant industrial wastes, red mud (RM) and lignin, via pyrolysis under N2 atmosphere, and its ability to treat wastewater containing various contaminants was comprehensively evaluated. A porous structure (BET surface area = 100.8 m2 g-1) was created and metallic Fe was formed in the MMBC owing to reduction of Fe oxides present in RM by lignin decomposition products during pyrolysis at 700 °C, which was closely associated with the transformation of liquid to gaseous pyrogenic products. The potential application of the MMBC was investigated for the removal of heavy metals (Pb(II) and Ni(II)), oxyanions (As(V) and Cr(VI)), dye (methylene blue), and pharmaceutical/personal care products (para-nitrophenol and pCBA). The aluminosilicate mineral, metallic Fe, and porous carbon matrix derived from the incorporation of RM and lignin contributed to the multifunctionality (i.e., adsorption, chemical reduction, and catalytic reaction) of the MMBC. Thus, engineered biochar composites synthesized from selected industrial wastes can be a potential candidate for environmental applications.

Engineered biochar composite fabricated from red mud and lipid waste and synthesis of biodiesel using the composite.

Co-pyrolysis of lipid waste and red mud was investigated to achieve valorization of red mud by fabricating biochar composite. For the further sustainable approach, this study intentionally employed carbon dioxide (CO2) as reaction medium in the co-pyrolysis process. The use of CO2 on co-pyrolysis of lipid waste and red mud enabled manipulation of the carbon distributions between pyrogenic products. CO2 expedited the thermal cracking of lipid waste and further reacted with lipid waste during the thermolysis. These mechanistic roles of CO2 were catalytically enhanced by the presence of mineral phases (Fe2O3) in red mud, thereby resulting in the enhanced formation of CO (40 times more at 550 °C). However, CO2 suppressed dehydrogenation of lipid waste (∼ 50%), which resulted in the different pathway for reducing iron oxide in red mud. Moreover, as an aspect of valorization of red mud, catalytic capability of biochar composite was evaluated. As a case study, biodiesel (FAMEs) were synthesized, and all experimental findings suggested that biochar composite could be an effective catalyst for biodiesel synthesis. As compare to biodiesel synthesis using silica (92% yield at 360 °C), the equivalent biodiesel yield was achieved with the biochar at much lower temperature (130 °C).

Fabrication of magnetic biochar as a treatment medium for As(V) via pyrolysis of FeCl3-pretreated spent coffee ground.

This study investigated the preparation of magnetic biochar from N2- and CO2-assisted pyrolysis of spent coffee ground (SCG) for use as an adsorption medium for As(V), and the effects of FeCl3 pretreatment of SCG on the material properties and adsorption capability of the produced biochar. Pyrolysis of FeCl3-pretreated SCG in CO2 atmosphere produced highly porous biochar with its surface area ∼70 times greater than that produced in N2 condition. However, despite the small surface area, biochar produced in N2 showed greater As(V) adsorption capability. X-ray diffraction and X-ray photoelectron spectrometer analyses identified Fe3C and Fe3O4 as dominant mineral phases in N2 and CO2 conditions, with the former being much more adsorptive toward As(V). The overall results suggest functional biochar can be facilely fabricated by necessary pretreatment to expand the applicability of biochar for specific purposes.

Fabrication of engineered biochar from paper mill sludge and its application into removal of arsenic and cadmium in acidic water.

An engineered biochar was fabricated via paper mill sludge pyrolysis under CO2 atmosphere, and its adsorption capability for As(V) and Cd(II) in aqueous solution was evaluated in a batch mode. The characterization results revealed that the biochar had the structure of complex aggregates containing solid minerals (FeO, Fe3O4 and CaCO3) and graphitic carbon. Adsorption studies were carried out covering various parameters including pH effect, contact time, initial concentrations, competitive ions, and desorption. The adsorption of As(V) and Cd(II) reached apparent equilibrium at 180min, and followed the pseudo-second-order kinetics. The highest equilibrium uptakes of As(V) and Cd(II) were 22.8 and 41.6mgg-1, respectively. The adsorption isotherms were better described by Redlich-Peterson model. The decrease in As(V) adsorption was apparent with the increase in PO43- concentration, and a similar inhibition effect was observed for Cd(II) adsorption with Ni(II) ion. The feasibility of regeneration was demonstrated through desorption by NaOH or HCl.