Two-step modification towards enhancing the adsorption capacity of fly ash for both inorganic Cu(II) and organic methylene blue from aqueous solution

Synthesis and adsorption performance of ultra-low silica-to-alumina ratio and hierarchical porous ZSM-5 zeolites prepared from coal gasification fine slag

Since the human consumption of coal is increasingly growing and coal-based solid wastes are discharged in large quantities, the resource utilization of coal-based solid wastes has been paid more attention. In the present work, for the first time, the coal gasification fine slag is subjected to prepare ZSM-5 zeolites with ultra-low n(SiO₂)/n(Al₂O₃) ratios (less than 20) and hierarchical pore structures. The increase in the concentration of the alkaline extract leads to the decrease of the crystallinity, the irregularity of the microscopic morphology, and the decrease of the specific surface area, resulting in the in-situ generation of mesopores within ZSM-5. Moreover, adsorption experiments demonstrate that ZSM-5-2M exhibits the best methylene blue adsorption performance at the pH of 9 with a removal rate of up to 82.07%, and it also has good adsorption performance in simulated real water samples. Furthermore, the adsorption performance of ZSM-5-2M on the malachite green, Rhodamine B, Congo red, and methyl orange has been investigated and it is found to be very effective for the adsorption of cationic dyes, and its adsorption performance for methylene blue and malachite green is reduced in the presence of anions.

Removal of COD in wastewater by magnetic coagulant prepared from modified fly ash

In this paper, magnetic coagulants (Fe-AFA, Fe-BFA) were prepared, by mixing acid-modified fly ash (AFA) and base-modified fly ash (BFA) with magnetic components, as adsorbents for chemical oxygen demand (COD) in desulfurization wastewater and their adsorption kinetics and mechanism are reported. BET, SEM, EDS, FTIR, XPS, magnetization intensity, and batch experiments on coagulation kinetic and adsorption isothermal characteristics of magnetic coagulants were carried out. The results show that Fe-AFA has the best COD adsorption performance and superparamagnetism, and the COD removal amounts can reach 5.69 mg/g, which is 112.43% higher than the raw fly ash. It was also found that the quasi-second-order kinetic and Langmuir equation could well describe the COD coagulation process. Thermodynamic tests results showed that the COD removal was a spontaneous, endothermic, and irreversible process. Reusability of magnetic coagulants was investigated. After five cycles, the COD removal amount of Fe-AFA was 2.74 mg/g. These findings provide a feasible method for environmental-benign utilization of fly ash as low-cost adsorbents in wastewater treatment.

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.

Zeolitic imidazolate framework-8/graphene oxide/magnetic chitosan nanocomposites for efficient removal of Congo red from aqueous solution

A novel bio-adsorbent toward Congo red with large adsorption capacity.

Adsorption of Cu(II) by phosphogypsum modified with sodium dodecyl benzene sulfonate

Phosphogypsum (PG) is a solid waste generated during the wet production of phosphoric acid, and stockpiling PG causes serious pollution to the environment. Therefore, we prepared an adsorption material modified with sodium dodecyl benzene sulfonate (SDBS) based on PG (SDBS@PG). SDBS@PG can be regenerated and used in several adsorption-desorption cycles. The optimum conditions for Cu(II) removal are as follows: the Cu(II) concentration is 10 mg/L, the amount of adsorbent is 1.6 g/L, the pH is 6, and the contact time is 60 min. Under these conditions, the removal rate is 99.23 %. The kinetic data of adsorption conform to the pseudo-second-order model. The equilibrium isotherm results are consistent with the Langmuir isotherm equation. Furthermore, plausible mechanisms were proposed: PG was modified with SDBS, which greatly improved the adsorption of Cu(II) onto PG. The main reason is that SDBS is adsorbed on the surface of PG by chemical action in the form of micelles and then Cu(II) is adsorbed on the anionic SDBS micelles of SDBS@PG due to chemical and electrostatic interactions. This work indicates that SDBS@PG can be used for the removal of Cu(II) and is qualified for practical application.