Processing of coal fly ash magnetic spheres for clay water flocculation

Mercury removal from coal combustion flue gas by pyrite-modified fly ash adsorbent

Pyrite and fly ash have certain advantages in adsorption and mercury oxidation. The pyrite-modified fly ash (PY + AC-FA) mercury adsorbent was prepared by mixing pyrite (PY) with acid-modified fly ash (AC-FA), which has better mercury removal effect than AC-FA. The experimental results of mercury adsorption show the following: when the reaction temperature is 50 °C, the best doping proportion of modified fly ash is 20 wt%, the mass proportion of pyrite to acid-modified fly ash is 4:1, and the flue gas flow rate is 1.0 L/min; the adsorbent has the best performance, and the adsorption rate of mercury reaches 91.92%. It was also found that the quasi-second-order kinetic model could describe the entire process of adsorption, and its adsorption process was mainly influenced by chemisorption. XRF, BET, SEM, XRD, and TG-DSG were used to characterize these adsorbents, and the mechanism of mercury removal of pyrite-modified fly ash adsorbent is inferred: Hg⁰ is first adsorbed on the surface of the adsorbent, and then oxidized to HgS by the active component FeS₂ in pyrite-modified fly ash.

On the state of the art of crystalline structure reconstruction of coal fly ash: A focus on zeolites

Coal fly ash (CFA) is fine particles generated from coal combustion, and large amount of CFA causes environmental pollution. Traditionally, CFA is added into construction materials, which has realized effective reduction. As the exploration of CFA properties goes deeper, finer utilization has been studied to maximize the recycling of CFA. Summarized from plenty of investigations, structure reconstruction has become the most crucial part for re-production as well as pre-treatments. Various zeolites and other complex materials have been synthesized by structure reconstruction. In this work, the state of the art of structure reconstruction were technically collated in the order of pre-treatments, mechanisms, specific techniques, and novel optimizing strategies. It has been found the crystalline types are closely related to the reaction conditions, that certain types of products could be obtained via accurate condition controls, especially the ratio of Si to Al. The current as-synthesized products were listed as well as their crystalline structure characteristics. Recently, combined materials and techniques have been innovatively investigated. However, the challenge remains as low purity, not only impurities in CFA but also different types of zeolites formed in one process.

Low-Cost Efficient Magnetic Adsorbent for Phosphorus Removal from Water

Adsorption using magnetic adsorbents makes the phosphorus removal from water simple and efficient. However, most of the reported magnetic adsorbents use chemically synthesized nanoparticles as magnetic cores, which are expensive and environmentally unfriendly. Replacing the nanomagnetic cores by cheap and green magnetic materials is essential for the wide application of this technique. In this paper, coal-fly-ash magnetic spheres (MSs) were processed to produce a cheap and eco-friendly magnetic core. A magnetic adsorbent, ZrO₂ coated ball-milled MS (BMS@ZrO₂), was prepared through a simple chemical precipitation method. Careful structural investigations indicate that a multipore structural amorphous ZrO₂ layer has grown on the MS core. The specific surface area of BMS@ZrO₂ is 48 times larger than that of the MS core. The highest phosphorus adsorption is tested as 16.47 mg g^-1 at pH = 2. The BMS@ZrO₂ adsorbent has a saturation magnetization as high as 33.56 emu g^-1, enabling efficient magnetic separation. Zeta potential measurements and X-ray photoelectron spectroscopy analysis reveal that the phosphorus adsorption of BMS@ZrO₂ is triggered by the electrostatic attraction and the ligand exchange mechanism. The BMS@ZrO₂ adsorbent could be reused several times after proper chemical treatment.

Leachability and adverse effects of coal fly ash: A review

Coal fly ash (CFA) is a valuable industrial solid waste, but conventional methods used for its disposal can lead to serious and long-lasting environmental issues. The study of technologies for CFA recycling has been of major concern, while the harm caused by CFA is only partially understood, limiting its reuse. In this review, the basic physico-chemical properties of CFA are introduced, followed by a systematic summary and discussion of the leachability of CFA via different leaching methods and the chemical speciation of some typical metal elements in CFA, which is related to its harmful effects. The specific harm that CFA causes to humans, wild animals, and plants and the study status of magnetic property of CFA are presented. Because of the pervasive concerns of many people, the utilisation of CFA in the USA and Europe and an economic and environmental analysis of its disposal is provided and discussed. Finally, some possible directions for future research involving CFA are proposed.

Flocculation Performance and Kinetics of Magnetic Polyacrylamide Microsphere under Different Magnetic Field Strengths

In this study, the flocculation performance and kinetics of magnetic cationic polyacrylamide (MCPAM) microspheres, compared with cationic polyacrylamide (CPAM), were systematically investigated under different magnetic field strengths. Flocculation performance was observed by jar test experiment. The density of flocs was estimated by the determination of floc settlement velocity and image analysis. The frequency distribution of floc size was measured with a Malvern Mastersizer instrument. When the diatomite suspension was treated by MCPAM and CPAM, the residual diatomite turbidity was 16.28 NTU and 244.13 NTU, respectively. The maximum turbidity removal efficiency of MCPAM was about 99.65% under 1000 Gauss magnetic field, which was higher than that (94.75%) of CPAM. The synergy of gravitational and magnetic fields for MCPAM promoted the formation of larger flocs with higher growth rates compared with CPAM. The effective density range of flocs in the MCPAM flocculation was increased to 10–252 kg m−3. The kinetic constants were calculated by monitoring the frequency of floc collisions. The increase of kinetic constant (k) to 25.81 × 10−11 s−1 suggested that interaction of contact and collision between magnetic flocs was sufficient. According to the evolution of the size and density of flocs under the synergy of gravitational and magnetic fields, the magnetic flocculation rate equation dN/dt=−1/9μρ−ρlg+ρkmHdH/dXai2−aj2−ai2e9μt/2ai2ρ+aj2e9μt/2aj2ρai+aj2 was derived. The study of magnetic flocculation kinetics can provide theoretical support for magnetic flocculation and is critical for the analysis of solid-liquid separation processes.

Airborne Magnetic Technoparticles in Soils as a Record of Anthropocene

Airborne magnetic particles in soils were studied in sites located in various distances to industrial plants. Chemical and mineral composition of soil samples were analysed. The highest values of the Pollution Load Index (PLI) calculated for several elements were noted for sites relatively distant from industrial plants. Soil samples exposed for the deposition of airborne particles were examined by means of magnetization versus an external applied magnetic field as well as 57Fe Mössbauer spectroscopy measurements showing a lack of correlation of the magnetic properties with total Fe content, which points toward a strong impact of the industrial activities. Magnetic fraction was extracted and studied using scanning electron microscopy with energy dispersive spectrometry. Two types of spherical particles were noted. Massive ones occurring in all sites and particles with a complex internal structure more abundant in sites situated closer to industrial plants. The presence of spherical magnetic particles formed in high temperature processes indicate their relatively long range transport in the atmosphere. Broad distribution, characteristic and easy for identification spherical form of these magnetic technoparticles, suggest that one can consider them as a record of the Anthropocene. Accumulation of such technoparticles is related to rapid industrialization in the post-World War II period.