ABSTRACT
Methylene blue (MB) is one of the most widely studied organic molecules in the treatment of wastewater. Sorption, biodegradation, photodegradation, electrochemical oxidation, ozonation, and other advanced oxidative processes are frequently used to remove this dye from water solutions. The unexpected degradation of MB adsorbed on magnetic biochar from aqueous solution was observed. We found that the conditions of handling, such as drying temperature and storage period, substantially influenced the stability of the dye fixed on the (magnetic) carbon adsorbents. Twelve substances were identified by mass spectrometry as products of decomposition, mostly demethylated, oxidated, and hydroxylated substances. The decomposition of MB was further investigated using non-magnetic carbon biochars and aluminosilicate mineral zeolite. Our findings of the spontaneous decomposition of MB and the identification of the species of degradation offer a new approach to evaluate the mechanism of adsorption, the process of regeneration, and the toxicity of treated solutions.
ABSTRACT
Large amounts of coal combustion products (as solid products of thermal power plants) with different chemical and physical properties cause serious environmental problems. Even though coal fly ash is a coal combustion product, it has a wide range of applications (e.g., in construction, metallurgy, chemical production, reclamation etc.). One of its potential uses is in zeolitization to obtain a higher added value of the product. The aim of this paper is to produce a material with sufficient textural properties used, for example, for environmental purposes (an adsorbent) and/or storage material. In practice, the coal fly ash (No. 1 and No. 2) from Czech power plants was firstly characterized in detail (X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), particle size measurement, and textural analysis), and then it was hydrothermally treated to synthetize zeolites. Different concentrations of NaOH, LiCl, Al2O3, and aqueous glass; different temperature effects (90-120 °C); and different process lengths (6-48 h) were studied. Furthermore, most of the experiments were supplemented with a crystallization phase that was run for 16 h at 50 °C. After qualitative product analysis (SEM-EDX, XRD, and textural analytics), quantitative XRD evaluation with an internal standard was used for zeolitization process evaluation. Sodalite (SOD), phillipsite (PHI), chabazite (CHA), faujasite-Na (FAU-Na), and faujasite-Ca (FAU-Ca) were obtained as the zeolite phases. The content of these zeolite phases ranged from 2.09 to 43.79%. The best conditions for the zeolite phase formation were as follows: 4 M NaOH, 4 mL 10% LiCl, liquid/solid ratio of 30:1, silica/alumina ratio change from 2:1 to 1:1, temperature of 120 °C, process time of 24 h, and a crystallization phase for 16 h at 50 °C.
ABSTRACT
The continued decrease in water quality requires new advances in the treatment of wastewater, including the preparation of novel, effective, environmentally friendly, and affordable sorbents of toxic pollutants. We introduce a simple non-conventional mechanochemical synthesis of magnetically responsive materials. Magnetic lignite and magnetic char were prepared by high-energy ball co-milling from either raw Slovak lignite or coal-based char together with a ferrofluid. The products were characterised by X-ray diffraction, electron microscopy, 57Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), volumetric magnetic susceptibility, and low-temperature nitrogen adsorption, and both magnetic carbons were comparatively tested as potential sorbents of As(V) oxyanions and Cd(II) cations in aqueous solutions. The magnetic char was an excellent sorbent of As(V) oxyanions (Qm = 19.9 mg/g at pH 3.9), whereas the magnetic lignite was less effective. The different sorption properties towards arsenic anions may have been due to different oxidation states of iron on the surfaces of the two magnetic composites (determined by XPS), although the overall state of iron monitored by Mössbauer spectroscopy was similar for both samples. Both magnetic composites were effective sorbents for removing Cd(II) cations (Qm (magnetic lignite) = 70.4 mg/g at pH 6.5; Qm (magnetic char) = 58.8 mg/g at pH 6.8).
ABSTRACT
Biochar is a promising immobilization tool for various contaminants in liquid wastes, aqueous solutions and soils. To further improve the sorption characteristics, a biochar/montmorillonite composite was produced and synthesized in an experimental pyrolysis reactor, using bamboo as biomass feedstock. The composite was characterized by physico-chemical and structural methods (FTIR, SEM, SEM/EDX, SSA, Low temperature nitrogen adsorption method). Based on these methods, the successful preparation of a bamboo based biochar/montmorillonite composite preparation has been demonstrated. The particles of montmorillonite were distributed across the biochar surface. The adsorption studies for removal nitrates from aqueous solutions were investigated by a batch method at laboratory temperatures. The experimental data were fitted by three adsorption models (Langmuir, Freundlich and DR; R2â¯>â¯0.93). The maximum adsorption capacity achieved by biochar at pH 4, was about 5â¯mgâ¯g-1 and by biochar/montmorillonite composite 9â¯mgâ¯g-1. The results suggest that the bamboo-based biochar/montmorillonite composite can be used effectively in the treatment of industrial effluents or waste water containing anionic pollutants such as nitrates.
