Simultaneous adsorption of ammonia and phosphate using ferric sulfate modified carbon/zeolite composite from coal gasification slag

Removal of Aqueous Antimony and Arsenic by Iron-Loaded Coal Gasification Slag Composite

The adsorption of Sb(V) and As(V) onto iron-loaded gasification slag composite material (Fe-GFS), as well as the possible mechanisms, was investigated. Batch experiments showed that in a single system, Fe-GFS sorbed As(V) to a greater extent than Sb(V) with the maximum adsorption capacity (pH 3.0) of 34.99 mg/g (0.47 mmol/g), while that of Sb(V) was 27.61 mg/g (0.23 mmol/g). In the composite system, the presence of low concentrations of Sb(V) reduced the adsorption efficiency of Fe-GFS for As(V), while the presence of high concentrations of Sb(V) actually promoted the adsorption of As(V). The presence of As(V) consistently inhibited the adsorption of Sb(V) by Fe-GFS. Compared to Fe-GFS, new peaks appeared in the FTIR spectra after adsorption, indicating the presence of Sb-O and As-O bonds on the surface after adsorption. XPS results showed that the adsorption of As(V) and Sb(V) led to a decrease in Fe-OH bonds, with a more significant decrease in Fe-OH bonds observed after the adsorption of As(V), indicating a stronger affinity of Fe-GFS for As(V) compared to Sb(V). Our results suggest that Fe-GFS is an efficient adsorbent with great potential for applications in water containing As(V) and Sb(V).

Magnesium doped biochar for simultaneous adsorption of phosphate and nitrogen ions from aqueous solution

Phosphorus (P) and Ammonium Nitrogen (N) are essential nutrients for plants and environmental stability. However, their excess in water causes eutrophication, damaging aquatic ecosystems. While adsorption is a promising solution, finding affordable and efficient adsorbents remains a challenge. In this study, magnesium (Mg), iron (Fe), and Mg/Fe doped biochars (BC) adsorbents were synthesized, and evaluated for adsorption of individual P and N and a P + N mixture from a solution and wastewater from a wastewater treatment plant. Compared to other adsorbents, Mg/BC showed excellent performance in adsorbing phosphorus (P) and ammonium nitrogen (N) from aqueous solutions. It demonstrated a large adsorption capacity of 64.65 mg/g and 62.50 mg/g from individual P and N solutions, and 30.3 mg/g and 27.67 mg/g from the P and N mixture solution, respectively. In addition, Mg/BC efficiently removed P and N from real-life wastewater. In the real wastewater, P and N removal efficiencies reached 88.30% and 59.36%, respectively. Kinetics analysis revealed that the pseudo-second-order model accurately described the adsorption of phosphorus (P) and ammonium nitrogen (N) in all solutions. The adsorbent followed the monolayer-Langmuir isotherm for N ions and the multilayer-Freundlich isotherm for P, indicating efficient adsorption processes. Thermodynamic experiments indicated that the adsorption of P and N was not only feasible but also occurred spontaneously in a natural manner. This study revealed that the strategic modification of biochar plays a crucial role in advancing effective wastewater treatment technologies designed for nutrient removal.

The adsorption properties and mechanisms of magnetic carbon-silicon composites in situ prepared from coal gasification fine slag

A novel magnetic carbon-silicon composite (Fe-HH-CGFS) was prepared from solid waste coal gasification fine slag (CGFS) by a two-step acid leaching and one-step chemical co-precipitation process, which was optimized using a 3-factor, 3-level Box-Behnken design and then analyzed for correlation. Fe-HH-CGFS was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) measurements. The results demonstrated that Fe-HH-CGFS had a reverse spinel structure with an average particle size of 5.14 nm, exhibiting a microporous/mesoporous structure with a specific surface area (SSA) of 196.84 m2 g-1 and pore volume of 0.346 cm3 g-1. Furthermore, Fe-HH-CGFS could achieve 97.59% removal efficiency of rhodamine B (RhB) under the optimal conditions: an initial concentration of RhB of 100 mg L-1, an adsorption time of 60 min, and a dosage of Fe-HH-CGFS of 1.0 g L-1. The pseudo-second-order model and the Langmuir isotherm satisfactorily described the adsorption behavior. The results indicated that the RhB removal process was a single-molecule layer endothermic adsorption, which is dominated by chemical adsorption reactions. This work is expected to provide an alternative route for the high-value utilization of CGFS and offer a valuable insight for the recycling of other solid wastes, aligning with the green development concept of "treating wastes with wastes".

Coal gasification crude slag based complex flocculants by two-step acid leaching process: synthesis, flocculation and mechanisms

Coal gasification crude slag (CGCS) is the side-product of the coal gasification process, and its effective utilization has attracted great attention. A novel flocculant of poly-aluminum-ferric-acetate-chloride (PAFAC) was synthesized based on the recovery of CGCS by a two-step acid leaching process, namely HCl-acid leaching and HAc-acid leaching, which was optimized by an acid leaching liquor volume ratio of HCl to HAc of 3 : 2, polymerization pH of 3.5, and reaction temperature and time of 70 °C and 3.0 h, respectively. The performance of PAFAC was further evaluated by kaolin simulated wastewater, domestic sewage, river water, and aquaculture wastewater. The results revealed that PAFAC was feasible for the removal of turbidity, chemical oxygen demand (COD) and total phosphorus (TP). Moreover, PAFAC was characterized by X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence spectrometry (XRF) and scanning electron microscopy (SEM), which proved that PAFAC was a kind of amorphous polyionic composite. Additionally, the acid leaching kinetics and flocculation mechanisms were further investigated. It was found that the acid leaching process was followed by the unreacted shrinkage core model, and the flocculation process was dominated by charge neutralization, adsorption bridging and precipitation net trapping. The work is expected to develop a new method for the safe disposal of CGCS and provide a novel way for the preparation of Fe-Al composite flocculants, especially, offering a potential strategy for the promotion of the additional value of the coal chemical industry.

A review of sustainable utilization and prospect of coal gasification slag

Currently, the storage of coal gasification slag (CGS) is continuously increasing, as the coal gasification technology develops, posing significant environmental hazards. Due to its volcanic ash characteristics and rich residual carbon, CGS has great potential for resource utilization, which has attracted the attentions of many scholars. This paper firstly introduces the compositions and properties of CGS. Then, it reviews the existing utilization methods of CGS, including Preparation of building materials, carbon-ash separation technology, ecological restoration, and cyclic blending. The advantages and disadvantages of various methods are compared. Subsequently, some high-value utilization methods of coal gasification slag are introduced, such as the preparation of high-performance activated carbon and zeolite, of which the feasibility and advantages are evaluated. Finally, some suggestions are put forward for future developing technologies. This paper aims to provide some references and inspiration for the utilization and environmental protection of CGS.

High adsorption capacity of ammonia nitrogen on hexagonal porous aluminosilicate derived from solid-waste bagasse bottom ash

This study investigates the use of a hexagonal-porous aluminosilicate (HAS) adsorbent derived from bagasse bottom ash (BBA), an agricultural solid waste, for the adsorption of ammonia nitrogen (NH3-N)-a key water pollutant from agricultural and farming activities. Sodium silicate derived from BBA via the alkaline fusion method was employed, resulting in energy savings due to a synthesis temperature 1.53 times lower than that of commercial sodium silicate synthesis. The sol-gel method was utilized to successfully synthesize HAS featuring a high surface area and porosity using the sodium silicate prepared from BBA. However, an increase in aluminum content resulted in a decrease in surface area and hexagonal porosity. In performance tests, the HAS(5) adsorbent exhibited the most efficient NH3-N removal, outperforming other adsorbents by 4.54-25.19 times across all initial concentrations. This enhanced efficiency can be attributed to its numerous acidic surface sites, enabling the bonding of NH3-N molecules through monolayer adsorption on the HAS surface.

Multitudinous components recovery, heavy metals evolution and environmental impact of coal gasification slag: A review

In recent years, the coal gasification industry has rapidly developed, becoming one of the most promising technologies in the advanced and clean coal chemical industry. As a result, the annual emission of coal gasification fine slag (CGFS) has continuously increased. The present situation of CGFS is regarded as a notorious waste in gasification plants and is rudely landfilled or deposited in slag yards, which leads to a large waste of land resources, the release of dangerous elements, and numerous pollution problems. Although CGFS is classified as industrial solid waste, its unique physical and chemical properties make it a valuable resource that cannot be overlooked. This paper focuses on the resource utilization technology and environmental impact of CGFS. The resource utilization of different components of CGFS has realized the evolution from waste to valuable substances. Moreover, during the disposal and utilization of CGFS, its environmental effects cannot be ignored. The main problems and future research directions are also further proposed. Efforts should be focused on the challenges of the technology, cost, and environmental protection in the application process to achieve industrial application, and ultimately committed to sustainable and green development goals, and promote the sustainable management and conservation of resources.

Simultaneous immobilization of ammonia and phosphorous by thermally treated sediment co-modified with hydrophilic organic matter and zeolite

The use of calcined sediments (CS) for thin-layer capping is an environment-friendly technology for controlling nitrogen (N) or phosphorus (P) release. However, the effects of CS derived materials and efficiency in controlling the sedimentary N/P ratio have not been thoroughly investigated. While zeolite-based materials have been proven efficient to remove ammonia, it is limited by the low adsorption capacity of PO₄^3-. Herein, CS co-modified with zeolite and hydrophilic organic matter (HIM) was synthesized to simultaneously immobilize ammonium-N (NH₄⁺-N) and remove P, due to the superior ecological security of natural HIM. Studies on the influences of calcination temperature and composition ratio indicated that 600 °C and 40% zeolite were the optimal parameters leading to the highest adsorption capacity and lowest equilibrium concentration. Compared with doping with polyaluminum chloride, doping with HIM not only enhanced P removal but also achieved higher NH₄⁺-N immobilization efficacy. The efficiency of zeolite/CS/HIM capping and amendment in prohibiting the discharge of N/P from sediments was assessed via simulation experiments, and the relevant control mechanism was studied at the molecular level. The results indicated that zeolite/CS/HIM can reduce 49.98% and 72.27% of the N flux and 32.10% and 76.47% of the P flux in slightly and highly polluted sediments, respectively. Capping and incubation with zeolite/CS/HIM simultaneously resulted in substantial reductions in NH₄⁺-N and dissolved total P in overlying water and pore water. Chemical state analysis indicated that HIM enhanced the NH₄⁺-N adsorption ability of CS owing to its abundant carbonyl groups and indirectly increased P adsorption by protonating mineral surface groups. This research provides a novel strategy to control sedimentary nutrient release by adopting an efficient and ecologically secure remediation method to rehabilitate eutrophic lake systems.

Phosphate removal mechanism of a novel magnesium slag-modified coal gasification coarse slag adsorbent

We used magnesium slag (MS) as a calcium source for modifying coal gasification coarse slag (CGCS) in the presence of NaOH to prepare a novel phosphate adsorbent (MS-CGCS). Ca₂SiO₄ in MS reacts with NaOH during the high-temperature synthesis process, with sodium displacing a part of the calcium content in Ca₂SiO₄ and entering the mineral lattice to form Na₂CaSiO₄. Hydroxide ions reacted with calcium in Ca₂SiO₄ to generate Ca(OH)₂ and decomposed into CaO at a high temperature. The two newly formed species participated in the phosphate removal. The MS-CGCS adsorbent showed good phosphate removal performance over a wide pH range, with a maximum phosphate adsorption capacity of 50.14 mg/g, which was significantly higher than that of other reported adsorbents. The Langmuir and pseudo-second-order models described the adsorption process well, indicating it being a monolayer and chemisorption process. The main mechanisms of phosphate removal are as follows: electrostatic interaction between the positively charged MS-CGCS and negatively charged phosphate ions; the inner-sphere complexation of oxides of metal, such as magnesium, aluminum, and calcium, with phosphate ions; and the precipitation of phosphate ions with calcium ions. Precipitation contributes to ~ 32% of the phosphate removal. This study provides a new method for the development of phosphate adsorbents while recycling CGCS and MS.

Preparation of a Chitosan/Coal Gasification Slag Composite Membrane and Its Adsorption and Removal of Cr (VI) and RhB in Water

At present, there are many kinds of pollutants, including dyes and heavy metal ions, in wastewater. It is very important to develop adsorbents that can simultaneously remove heavy metal ions and dyes. In this study, a renewable composite membrane material was synthesized using chitosan and treated coal gasification slag. The Cr (VI) maximum adsorption capacity of the composite membrane was 50.0 mg/L, which was 4.3~8.8% higher than that of the chitosan membrane. For the adsorption of RhB, the removal rate of the chitosan membrane was only approximately 5.0%, but this value could be improved to 95.3% by introducing coal gasification slag. The specific surface area of the chitosan membrane could also be increased 16.2 times by the introduction of coal gasification slag. This is because coal gasification slag could open the nanopores of the chitosan membrane (from 80 μm to 110 μm). Based on the adsorption kinetics and adsorption mechanism analysis, it was found that the adsorption of Cr (VI) occurred mainly through the formation of coordination bonds with the amino groups on the molecular chains of chitosan. Meanwhile, RhB adsorption occurred through the formation of hydrogen bonds with the surface of coal gasification slag. Additionally, coal gasification slag can improve the mechanical properties of the chitosan membrane by 2.2 times, which may facilitate the practical application of the composite membrane. This study provides new insight into the adsorbent design and the resource utilization of coal gasification slag.