Quasi Natural Approach for Crystallization of Zeolites from Different Fly Ashes and Their Application as Adsorbent Media for Malachite Green Removal from Polluted Waters

Abstract

Worldwide disposal of multi-tonnage solid waste from coal-burning thermal power plants (TPPs) creates serious environmental and economic problems, which necessitate the recovery of industrial waste in large quantities and at commercial prices. Fly ashes (FAs) and slag from seven Bulgarian TPPs have been successfully converted into valuable zeolite-like composites with various applications, including as adsorbents for capturing CO2 from gases and for removal of contaminants from water. The starting materials generated from different types of coal are characterized by a wide range of SiO2/Al2O3 ratio, heterogeneous structure and a complex chemical composition. The applied synthesis procedure resembles the formation of natural zeolites, as the raw FAs undergo long-term self-crystallization in an alkaline aqueous solution at ambient temperature. The phase and chemical composition, morphology and N2 adsorption of the final zeolite products were studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-Ray Diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. The growth of faujasite (FAU) crystals as the main zeolite phase was established in all samples after 7 and 14 months of alkaline treatment. Phillipsite (PHI) crystals were also observed in several samples as an accompanying phase. The final products possess specific surface area over 400 m2/g. The relationships between the surface properties of the investigated samples and the characteristics of the raw FAs were discussed. All of the obtained zeolite-like composites were able to remove the highly toxic dye (malachite green, MG) from water solutions with efficiency over 96%. The experimental data were fitted with high correlation to the second-order kinetics.

Production of nanostructured crystalline composite using residual ashes from flocculated sludge burning process in a poultry slaughterhouse wastewater treatment system

“…Between 2017 and 2018, countries such as India, China, United States, and Germany produced around 350 million tons of residual ash, with an estimated 700 million tons worldwide [1,3]. These residual ashes from the burning process are usually used on an industrial scale to make construction materials like Portland cement and/or refractory bricks, but the unused parts of this waste end up being stored in an area of the industry or disposed of as garbage, which can lead to soil degradation and pose a risk to groundwater bodies [4][5][6]. To avoid this risk, the use of these residual ashes for the synthesis of zeolitic material has been studied in the literature [7,8].…”

Characterization of the Physical, Chemical, and Adsorption Properties of Coal-Fly-Ash–Hydroxyapatite Composites

“…The use of carbon sorbents for dye removal is widely known [9,16]. Low-cost sorbents and coated or composite magnetic particles [10] have also been studied for this application, as have natural and synthetic zeolites [17][18][19][20]. Due to the frequent coexistence of dyes and heavy metals in industrial wastewater, adsorbents that enable the removal of both types of pollutants are being sought.…”

“…Power-plant byproducts-e.g., blast furnace slag [35,42] and steel slag [43]-are also good calcium substrates for the hydrothermal method. However, other byproducts, such as solid slag from bottom ash and fly ash from coal combustion [44,45]; and lignite, brown, and anthracite coal combustion [20], are useful sources of SiO 2 and Al 2 O 3 for the synthesis of zeolite. Furthermore, coal ash or steel slag containing SiO 2 , Al 2 O 3 , and CaO can be used to obtain zeolite-HAp nanocomposites [46,47].…”