Adsorptive removal of organics from aqueous phase by acid-activated coal fly ash: preparation, adsorption, and Fenton regenerative valorization of “spent” adsorbent

Abstract

Raw coal fly ash was activated to an adsorbent by sulfuric acid impregnation. The activation condition, the adsorption capacity, and the regenerative valorization of the adsorbent were studied. The results show that the optimal preparation conditions of the adsorbent are [HSO] = 1 mol L, activation time = 30 min, the ratio of coal fly ash to acid = 1:20 (g:mL), calcination temperature = 100 °C. The adsorption of p-nitrophenol on the adsorbent accords with the pseudo-second-order kinetic equation and the adsorption rate constant is 0.089 g mg min. The adsorption on this adsorbent can be considered enough after 35 min, when the corresponding adsorption capacity is 1.07 mg g (85.6% of p-nitrophenol removal). Compared with raw coal fly ash, the adsorbent has a stable adsorption performance at low pH range (pH = 1-6) and the adsorption of p-nitrophenol is an exothermic process. Ninety minutes is required for the regenerative valorization of saturated adsorbent by Fenton process. The regenerative valorization for this saturated adsorbent can reach 89% under the optimal proposed conditions (30 °C, pH = 3, [HO] = 5.0 mmol L, [Fe] = 5.5 mmol L). Within 15 experimental runs, the adsorbent has a better and better stability with the increase of experimental runs. Finally, the mechanism of activating coal fly ash is proposed, being verified by the results of the SEM and BET test.

Eco-Friendly Materials Obtained by Fly Ash Sulphuric Activation for Cadmium Ions Removal

“…One significant observation is that the results of XRD analysis revealed that quartz (Q) presents the highest intensity—mullite (M) and hematite (He); the mainly crystalline phases of the unmodified fly ash [ 26 ] can also be identified in FA/H 2 SO 4 . Additionally, FA/H 2 SO 4 shows a prominent peak at 2 theta = 25.63° that can be attributed to modernite (MOR)[Na 8 (H 2 O) 24 ] [Si 40 Al 8 O 96 ] [ 35 , 36 ]. In the case of FA/H 2 SO 4 +Cd 2+ the peaks can be observed in minor intensity.…”

“…On the other hand, after Cd 2+ adsorption there was a shift in the bands between 1700 cm −1 and 400 cm −1 , which proves the adsorption process of Cd 2+ on the FA/H 2 SO 4 sample [33,34]. One significant observation is that the results of XRD analysis revealed that quartz (Q) presents the highest intensity-mullite (M) and hematite (He); the mainly crystalline phases of the unmodified fly ash [26] [35,36]. In the case of FA/H 2 SO 4 +Cd 2+ the peaks can be observed in minor intensity.…”

Photocatalytic degradation of glyphosate using Ce/N co-doped TiO2 with oyster shell powder as carrier under the simulated fluorescent lamp

“…Therefore, the combination of photocatalysts and highly efficient adsorbent materials to achieve adsorptionphotocatalytic "cooperation" can also effectively increase photocatalytic efficiency. Currently, the use of waste materials to prepare new, inexpensive, "green" adsorbents is a hot topic of research (Abbas 2014;Jiang et al, 2018), such as quartz particles, fly ash, zeolite and other natural materials and waste slag-based adsorbent materials (Cao et al, 2018;Wang et al, 2018;Alvarez-García et al, 2019). The oyster is a highly productive and environmentally adaptable aquatic organism that absorbs elements from the surrounding environment and forms a shell with a carbonate composition through the secretion of its soft body, rich in CaCO 3 and a large number of micropores.…”

Optimization of Preparation Conditions of Modified Oyster Shell Powder/Ce-N-TiO<sub>2</sub> by Response Surface Methodology (RSM)

“…The adsorbent may adsorb a large number of organic pollutant molecules, thus facilitating the reaction between the organic molecules and the active radicals formed on the TiO 2 surface, forming an adsorption-catalysis photodegradation pathway. Currently, the use of waste materials to prepare new, inexpensive, "green" adsorbents is a hot research topic [14] [15], such as quartz particles, fly ash, zeolite, and other natural materials and waste residue-based adsorbent materials [16] [17] [18] [19]. However, there are not many reports on the preparation of composite photocatalysts with adsorption-photocatalytic synergy by combining the above-mentioned types of adsorbent materials with modified TiO 2 .…”