Characterization and adsorption applications of composite biochars of clay minerals and biomass

Clay mineral as catalysis for controlling the nitrogen containing pollutants during sewage sludge pyrolysis

Pyrolysis technology is considered one of the most promising processes for the environmentally friendly disposal of sewage sludge (SS), as it can neutralize pathogens, reduce hazardous substances, and promote the immobilization of heavy metals. However, nitrogen-containing gases produced in SS pyrolysis can be converted to nitrogen oxides, causing serious environmental pollution. In this study, we investigated the evolution of the nitrogen (N) element in rapid pyrolysis of SS and explored the effect of clay minerals (attapulgite, montmorillonite, and kaolin) in regulating N conversion. The results showed that the higher temperature (800 °C) could promote the conversion of pyrroles/pyridines and NOx precursors in char to N2 (the conversion rate was 32.76 %), and clay minerals catalyzed the cleavage of N-containing macromolecules in the bio-oil, reducing the N content in bio-oil from 28.70 % to 6.23 %, and was conducted to realize the denitrification of bio-oil. Notably, the attapulgite (ATP) on N migration was more effective and could reduce the yield of NOx precursors from 23.80 % to 10.55 % by capturing NH4* and inhibiting the secondary reaction, while catalyzing the removal of N2 from pyridine/pyrrole (N2 production increased to 34.38 %). MgO and CaO in the clays played a major role in facilitating the conversion of char-N to N2, and clay structures loading on the biochar surface promoted the catalysis of N-containing volatiles to N2 by metal oxides. This study provides a viable and harmless approach to SS minimization.

Impacts of kaolinite enrichment on biochar and hydrochar characterization, stability, toxicity, and maize germination and growth

In this study, biochar (BC) and hydrochar (HC) composites were synthesized with natural kaolinite clay and their properties, stability, carbon (C) sequestration potential, polycyclic aromatic hydrocarbons (PAHs) toxicity, and impacts on maize germination and growth were explored. Conocarpus waste was pretreated with 0%, 10%, and 20% kaolinite and pyrolyzed to produce BCs (BC, BCK10, and BCK20, respectively), while hydrothermalized to produce HCs (HC, HCK10, and HCK20, respectively). The synthesized materials were characterized using X-ray diffraction, scanning electron microscope analyses, Fourier transform infrared, thermogravimetric analysis, surface area, proximate analyses, and chemical analysis to investigate the distinction in physiochemical and structural characteristics. The BCs showed higher C contents (85.73-92.50%) as compared to HCs (58.81-61.11%). The BCs demonstrated a higher thermal stability, aromaticity, and C sequestration potential than HCs. Kaolinite enriched-BCs showed the highest cation exchange capacity than pristine BC (34.97% higher in BCK10 and 38.04% higher in BCK20 than pristine BC), while surface area was the highest in kaolinite composited HCs (202.8% higher in HCK10 and 190.2% higher in HCK20 than pristine HC). The recalcitrance index (R50) speculated a higher recalcitrance for BC, BCK10, and BCK20 (R50 > 0.7), minimal degradability for HCK10 and HCK20 (0.5 < R50 < 0.7), and higher degradability for biomass and HC (R50 < 0.5). Overall, increasing the kaolinite enrichment percentage significantly enhanced the thermal stability and C sequestration potential of charred materials, which may be attributed to changes in the structural arrangements. The ∑ total PAHs concentration in the synthesized materials were below the USEPA's suggested limits, indicating their safe use as soil amendments. Germination indices reflected positive impacts of synthesized charred materials on maize germination and growth. Therefore, we propose that kaolinite-composited BCs and HCs could be considered as efficient and cost-effective soil amendments for improving plant growth.

Preparation and characterization of hemicellulose films reinforced with amino polyhedral oligomeric silsesquioxane for biodegradable packaging

Biomass is one of the powerful alternatives to petroleum-based packaging materials. Herein, carboxymethyl hemicellulose (CMH) based films (CPF) were prepared using a convenient strategy. The chains of CMH provided the necessary supporting matrix, and the aminopropyl polyhedral oligomeric silsesquioxane (POSS-NH2) regulated the thermal and barrier properties of the CPF. The secondary amide groups and hydrogen bond were appeared in chemical structure, and SEM-EDS results indicated the preferable dispersion and compatibility of POSS-NH2 in CPFs. The thermal degradation temperature (Tonset > 260 °C), the coefficient of linear thermal expansion and glass transition temperature (Tg > 130 °C) have been improved by introduction of POSS-NH2. The tensile strength of CPF showed a higher level of 39.43 MPa with the POSS-NH2 loading of 20 wt%, which was 18.8 % higher than that of CMH film. More importantly, water vapor barrier property of films almost improved by two times, and its value is reduced to 18.82 g m-2 h-1. The shelf life of blueberry was effectively extended by the CPF coating for one week compared with commercial PE film. Therefore, CPF films displayed effective thermal performances, water vapor barrier characteristic and biodegradability, which might be exploited in packaging material for food application.

Characterization and Co-Adsorption Mechanism of Magnetic Clay-Biochar Composite for De-Risking Cd(II) and Methyl Orange Contaminated Water

The application of the adsorption method in sewage treatment has recently become a hot spot. A novel magnetic clay-biochar composite (BNT-MBC) was fabricated by co-pyrolysis of bentonite and biomass after being impregnated with Fe (NO3)3·9H2O. Its adsorption capacity for Cd(II) and methyl orange was approximately doubled, reaching a maximum of 26.22 and 63.34 mg/g, and could be easily separated from the solution by using external magnets with its saturation magnetization of 9.71 emu/g. A series of characterizations including surface morphology and pore structure, elemental analysis, functional group analysis and graphitization were carried out, showing that the specific surface area was increased 50 times by loading 20 wt.% bentonite, while its graphitization and oxygen-containing functional groups were also enhanced. The isotherm fitting indicated that Cd(II) was adsorbed in multiple layers, while methyl orange was in both monolayer and multilayer adsorptions. The kinetic fitting indicated that chemisorption was the rate-limiting step of both, and it was also a complex process controlled by two steps with the fitting of intra-particle diffusion. In the binary system of Cd(II) and methyl orange, the co-existing pollutants facilitated the adsorption of the original one, and there was no competition between adsorption sites of Cd(II) and methyl orange. BNT-MBC also exhibited good reusability and can be magnetically recovered for recycling. Thus, the magnetic clay-biochar composite BNT-MBC is a cost-effective and promising adsorbent for simultaneous removing Cd(II) and methyl orange from wastewater.

Simultaneous Recovery of Nitrogen and Phosphorus from Sewage by Magnesium Ammonium Phosphate Method with Magnesium-Loaded Bentonite

Excessive nitrogen (N) and phosphorus (P) result in serious eutrophication of water. In this study, magnesium modified acid bentonite was prepared by the impregnation method, and nitrogen and phosphorus were simultaneously removed by the magnesium ammonium phosphate method (MAP), which solved the problem of the poor adsorption capacity of bentonite. The morphology and structure of MgO-SBt were characterized by XRD, FT-IR, SEM, EDS, XPS, BET, etc. The results show that the acidified bentonite can increase the distance between bentonite layers, the layer spacing is expanded to 1.560 nm, and the specific surface area is expanded to 95.433 m²/g. After Mg modification, the characteristic peaks of MgO appear at 2θ of 42.95°, 62.31°, and 78.72°, indicating that MgO has been successfully loaded and that MgO bonded to the surface and interior pores of the acidified bentonite, boosting adsorption performance. When the dosage of MgO-SBt is 0.25 g/L, pH = 9, and N/P ratio is 5:1, the maximum adsorption capacity of MgO-SBt for N and P can reach 193.448 mg/g and 322.581 mg/g. In addition, the mechanism of the simultaneous adsorption of nitrogen and phosphorus by MgO-SBt was deeply characterized by the kinetic model, isothermal adsorption model, and thermodynamic model. The results showed that the simultaneous adsorption of nitrogen and phosphorus by MgO-SBt was chemisorption and a spontaneous exothermic process.