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The present work aims to increase the alumina percentage recovery (APR) extracted from kaolinviathe addition of 0.5–4.0 wt.% charcoal as a thermochemical fluxing agent in the lime-sintering process at 1260–1360°C. The transformation, microstructural and microtextural changes and self-disintegration performance were characterized using thermogravimetric analysis and differential scanning calorimetry, X-ray diffraction/X-ray fluorescence, scanning electron microscopy coupled with energy-dispersive spectroscopy and laser diffraction particle-size distribution analysis. The optimum enhancement of APR, from 77.7% to 87.40%, was obtained by sintering at 1360°C with the addition of 1.5% charcoal. With further increase of the charcoal content to 4%, the APR reduced to 75.6%. Combustion of ≤1.5% charcoal provided additional heat that amorphized the crystalline calcium aluminate into highly leachable amorphous phases with improved self-disintegration efficiency. Sintering at temperatures of >1360°C or with charcoal contents >4% led to mullite crystallization and decreased alumina leachability, thereby reducing the APR. Charcoal is a cost-effective and energy-efficient activator to increase the APR extracted from kaolin.

The increase of global environmental restrictions concerning solid and liquid industrial waste, in addition to the problem of climate change, which leads to a shortage of clean water resources, has raised interest in developing alternative and eco-friendly technologies for recycling and reducing the amount of these wastes. This study aims to utilize Sulfuric acid solid residue (SASR), which is produced as a useless waste in the multi-processing of Egyptian boiler ash. A modified mixture of SASR and kaolin was used as the basic component for synthesizing cost-effective zeolite using the alkaline fusion-hydrothermal method for the removal of heavy metal ions from industrial wastewater. The factors affecting the synthesis of zeolite, including the fusion temperature and SASR: kaolin mixing ratios, were investigated. The synthesized zeolite was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), particle size analysis (PSD) and N2 adsorption-desorption. The SASR: kaolin weight ratio of 1:1.5 yields faujasite and sodalite zeolite with 85.21% crystallinity, which then shows the best composition and characteristics of the synthesized zeolite. The factors affecting the adsorption of Zn2+, Pb2+, Cu2+, and Cd2+ ions from wastewater on synthesized zeolite surfaces, including the effect of pH, adsorbent dosage, contact time, initial concentration, and temperature, have been investigated. The obtained results indicate that a pseudo-second-order kinetic model and Langmuir isotherm model describe the adsorption process. The maximum adsorption capacities of Zn2+, Pb2+, Cu2+, and Cd2+ ions onto zeolite at 20 °C were 12.025, 15.96, 12.247, and 16.17 mg·g−1, respectively. The main mechanisms controlling the removal of these metal ions from aqueous solution by synthesized zeolite were proposed to be either surface adsorption, precipitation, or ion exchange. The quality of the wastewater sample obtained from the Egyptian General Petroleum Corporation (Eastern Desert, Egypt) was highly improved using the synthesized zeolite and the content of heavy metal ions was significantly reduced, which enhances the utilization of the treated water in agriculture.

The water leaching solid residues (WLSR) obtained from salt-roasting Egyptian boiler ash are considered an essential secondary resource for (13%) nickel and (5.6%) zinc extraction. Hence, the current study aims for the cost-effective and high purity Ni, Zn, Fe and Mg metal ion extraction from (WLSR) using a sulfuric acid leaching process. The factors affecting the percentage recovery of Ni, Zn, Fe and Mg from WLSR, including leaching temperature, time, acid concentration and solid/liquid ratio, have been investigated. The obtained leaching solutions were analyzed chemically using ICP, and the different precipitates were analyzed mineralogically using XRD and EDX analysis and chemically using XRF. The maximum percentage recovery of Ni, Zn, Fe and Mg was 95.02%, 90.13%, 66.29% and 75.73%, which was obtained under the optimum leaching conditions of 8% H2SO4 concentration and 1/15 solid/liquid ratio at 85 °C for 240 min. The effect of pH, Fe2O3 dosage as nucleating agent and the precipitation duration on iron removal and Ni and Zn loss have been thoroughly studied. It has been found that >95% of the contained iron impurity can be removed, while nickel and zinc losses are around 4.2% and 3.8%, respectively. Additionally, a pH of 6 and 0.45 mol/L concentration of H2C2O4 was utilized to precipitate Mg as MgC2O4.2H2O, demonstrating that the precipitation efficiency of Mg reaches 96.9%. Nickel and zinc precipitation efficiency was 92.25% and 85.51%, respectively, by raising the solution pH to approximately 9. The kinetic of Ni and Zn dissolution has been investigated to explain the mechanism prevalent and the factors influencing the leaching process. It has been found that the nickel leaching kinetic is controlled by both diffusion through an inert porous layer and by chemical reaction with an activation energy of 20.25 kJ.mol−1. Meanwhile, the kinetic of zinc leaching is controlled by solid product layer diffusion with an activation energy of 11.67 kJ mol−1.