Clean production of porous-Al(OH)3 from fly ash

Simultaneous separation of Fe & Al and extraction of Fe from waste coal fly ash: Altering the charge sequence of ions by electrolysis

A significant amount of coal fly ash is generated and this type of waste material causes severe environmental hazards. Metal (Al and Fe) extraction from coal fly ash is beneficial to the resource utilization of waste coal fly ash. However, the coexistence of Al and Fe in coal fly ash means that the separation of Al and Fe is required, which is a key and difficult step to prepare high value-added products from coal fly ash. This work presents a novel electrolysis method to alter the charge sequence of Al³⁺, Fe³⁺, and H₂O, leading to a process different from their natural tendency for simultaneous separation of Fe³⁺ and Al³⁺, and extraction of Fe. The single iron removal efficiency was 43.48%, and the aluminum extraction efficiency was <0.30% under optimal conditions. The iron product had a purity of 98.3 wt% Fe, 0.45 wt% Al, and 0.18 wt% S. This process occurs without chemical additions and expensive membranes, avoiding impurity introduction, slag generation, and membrane limitations. Fe(s), H₂(g), Al₂(SO₄)₃(aq), and O₂(g) are the main products during the electrolysis. Flake Fe is selectively produced instead of colloidal Fe(OH)₃. Fe is a magnetic substance and is easier to remove from the solution by magnets than colloidal Fe(OH)₃. H₂ is a green fuel. Wastewater (Al₂(SO₄)₃(aq)) can be directly used to further extract alumina. Therefore, this study provides an alternative method of zero pollution discharge for simultaneous separation of Fe³⁺ and Al³⁺, and extraction of Fe from coal fly ash leachate.

Effects of aging on surface properties and endogenous copper and zinc leachability of swine manure biochar and its composite with alkali-fused fly ash

Biochar aging is a key factor leading to the decline of biochar stability and the release of endogenous pollutants. This study investigated the effects of five artificial and simulated aging processes on the surface properties and endogenous copper (Cu) and zinc (Zn) leachability of swine manure biochar and its composite with alkali-fused fly ash. Aging obviously reduced carbon (C) content on the surface of swine manure biochar and increased oxygen (O) content. Among all the aging treatments, high-temperature aging had the greatest effect on C content. Following the aging treatments, the C-C bond contents on the surfaces of swine manure biochar decreased significantly, whereas the C-O bonds increased significantly; however, there were less changes in the amounts of C-C and C-O bonds on the surfaces of modified biochar than on swine manure biochar. Aging significantly enhanced the leaching toxicity of Cu and Zn, and Zn availability and bioaccessibility in swine manure biochar and modified biochar. However, it minimized Cu availability and bioaccessibility, especially under high-temperature aging. Greater amounts of Zn than Cu were extracted from swine manure biochar and modified biochar. However, under all the aging treatments, the leaching toxicity, availability, and bioaccessibility of Cu and Zn in modified biochar were significantly lower than in swine manure biochar. This implies that modified biochar application poses lower environmental risks than swine manure biochar.

Extraction of lithium and aluminium from bauxite mine tailings by mixed acid treatment without roasting

Bauxite mine tailings can be used as the reserve resources of aluminium and lithium. In this study, a less energy consumption treatment method for extracting aluminium and lithium from bauxite mine tailings has been proposed, which used mixed acid to leach aluminium and lithium from tailings directly, avoided roasting for reducing energy consumption, and obtained effective results.The minerals in the tailings are kaolinite, diaspore, boehmite, anatase and illite, among others. The minerals have fine dissemination sizes and low liberation. Under the leaching conditions of Al and Li of an acid concentration of 60%, a liquid-solid ratio of 4 mL/g, a reaction temperature of 100 °C and a reaction time of 3 h, the highest leaching rates of Al and Li are 88.64% and 96.35%, respectively. In the leaching process, phosphoric acid reacts with Al and Li in the strong acidic environment provided by sulphuric acid to produce heteropoly acids or heteropoly acid salts that dissolve in the solution.

Enhancing the removal efficiency of methylene blue in water by fly ash via a modified adsorbent with alkaline thermal hydrolysis treatment

High efficiency of methylene blue adsorbent from waste coal fly ash by treatment with alkaline thermal hydrolysis.

Complete Extraction of Amorphous Aluminosilicate from Coal Fly Ash by Alkali Leaching under Atmospheric Pressure

One of the potential sources of alumina and mesoporous silica is the coal-fired thermal plants waste known as the coal fly ash (CFA). The studies of the alumina extraction from CFA are often focused on the preliminary desilication, but the efficiency of the alkali desilication is low due to formation of the desilication product—Na6[Al6Si6O24]·Na2X (DSP). This research is focused on the possibility of CFA desilication without formation of DSP using a leaching process with higher liquid to solid ratios (L/S) and alkali concentrations. The experimental data were analyzed using an artificial neural network (ANN) machine learning method and a shrinking core model (SCM). The investigation of the CFA morphology, chemical and phase composition before and after leaching were carried out by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray diffraction (XRD). The present work shows that it is possible to avoid formation of DSP if using the L/S ratio >20 and concentration of Na2O—400 g/L during CFA leaching. The kinetics analysis by SCM showed that the process is limited by the surface chemical reaction at T <100 °C, and by diffusion through the product layer at T >100 °C, respectively. The SEM images of the solid residue after NaOH leaching under conditions that prevent the DSP formation show mullite particles with an acicular structure.

A Study on Mn-Fe Catalysts Supported on Coal Fly Ash for Low-Temperature Selective Catalytic Reduction of NOX in Flue Gas

A series of Mn0.15Fe0.05/fly-ash catalysts have been synthesized by the co-precipitation method using coal fly ash (FA) as the catalyst carrier. The catalyst showed high catalytic activity for low-temperature selective catalytic reduction (LTSCR) of NO with NH3. The catalytic reaction experiments were carried out using a lab-scale fixed-bed reactor. De-NOx experimental results showed the use of optimum weight ratio of Mn/FA and Fe/FA, resulted in high NH3-SCR (selective catalytic reduction) activity with a broad operating temperature range (130–300 °C) under 50000 h−1. Various characterization methods were used to understand the role of the physicochemical structure of the synthesized catalysts on their De-NOx capability. The scanning electron microscopy, physical adsorption-desorption, and X-ray photoelectron spectroscopy showed the interaction among the MnOx, FeOx, and the substrate increased the surface area, the amount of high valence metal state (Mn4+, Mn3+, and Fe3+), and the surface adsorbed oxygen. Hence, redox cycles (Fe3+ + Mn2+ ↔ Mn3+ + Fe2+; Fe2+ + Mn4+ ↔ Mn3+ + Fe3+) were co-promoted over the catalyst. The balance between the adsorption ability of the reactants and the redox ability can promote the excellent NOx conversion ability of the catalyst at low temperatures. Furthermore, NH3/NO temperature-programmed desorption, NH3/NO- thermo gravimetric-mass spectrometry (NH3/NO-TG-MS), and in-situ DRIFTs (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) results showed the Mn0.15Fe0.05/FA has relatively high adsorption capacity and activation capability of reactants (NO, O2, and NH3) at low temperatures. These results also showed that the Langmuir–Hinshelwood (L–H) reaction mechanism is the main reaction mechanism through which NH3-SCR reactions took place. This work is important for synthesizing an efficient and environmentally-friendly catalyst and demonstrates a promising waste-utilization strategy.