The constant discharge of large quantities of toxic substances due to human activities has led to a global environmental issue. Numerous industrial sectors’ effluents, which include coal-based power plants, mineral extraction activities, electroplating processes, as well as battery...

Wastewater discharges from industrial processes typically include elevated concentrations of contaminants, which largely consist of potentially harmful chemicals such as heavy metals. These contaminants are characterized by their slow rate of decomposition. Hence, the removal of these metallic ions from effluents poses a challenge. Among different treatments, the adsorption approach has considerable potential due to its ability to effectively eliminate both soluble and insoluble pollutants from effluent, even at lower levels of concentration. Of various wastes, fly ash (FA) material has been the subject of attention because it is abundant, has favorable qualities, and contains a high percentage of minerals. This review investigates multiple facets, with a specific focus on the application of FA, an industrial byproduct, as an adsorbent in removing heavy metals. A comprehensive examination was conducted on a range of concerns pertaining to the pollution caused by metallic ions, including the underlying causes, levels of contamination, health implications of heavy metals, and removal methods. Multiple factors were found to affect the adsorption process. Of all the factors, the pH value considerably influences the elimination of heavy metals. An acidic pH range of 2.5–4.5 was found to be optimal for achieving the highest possible elimination of As(V), Cu(II), Hg(II), and Cr(VI). The latter elimination rate reached 89% at the optimal pH level. Most heavy metals’ adsorption isotherms conformed to the Langmuir or Freundlich models, while the pseudo-second-order kinetics provided a satisfactory match for their removal. Using a raw FA, adsorption capacities were achieved in the removal of metallic ions, Ni(II), Pb(II), and Cr(VI), that ranged from 14.0 to 23.9 mg g⁻¹. Meanwhile, the FA-zeolite showed a remarkable capacity to adsorb ions Mn(II), Ni(II), Cd(II), Cu(II), and Pb(II), with values ranging from about 31 to 66 mg g⁻¹. The cost analysis showed that the treatment of FA is economically advantageous and may result in significant cost reductions in comparison to commercial adsorbents. In summary, FA is an inexpensive waste material with potential for water treatment applications and several other purposes due to its excellent chemical and mineralogical composition.

The degradation kinetics of Direct Blue 15 (DB15), a diazo dye, were studied over a suspended and immobilized TiO₂ catalyst. For all experiments, the kinetics experiments were performed in a swirl flow photoreactor under the influence of UV light. The effect of different parameters: dye concentration, catalyst loading, and light intensity, on the DB15 kinetics was investigated. The kinetic rates were assessed using apparent $\left({\mathrm{k}}_{\mathrm{a}}\right)$ approach, a single value of reaction rate $\left({\mathrm{k}}_{\mathrm{r}}\right)$ and adsorption constant$\left(\mathrm{K}\right)$, and approach of ${\mathrm{k}}_{\mathrm{r}}$ as of variable. The DB15 mineralization was discussed as well. Using a dip-coating device, the P25 catalyst was deposited on a Pyrex glass. The thin film surface characterization was examined. The coated catalyst was evaluated by checking the effect of two variables: initial dye concentration and light intensity on the DB15 kinetics. In terms of the ${\mathrm{k}}_{\mathrm{a}}$ approach, the results demonstrated that DB15 degradation is described by the pseudo first-order kinetics model. The Langmuir-Hinshelwood (L-H) model was fitted well with the experimental data for the number of process variables. L-H constant ${\mathrm{k}}_{\mathrm{r}}$ was determined as a function of three parameters: initial dye concentration, catalyst loading, and light intensity. The ${\mathrm{k}}_{\mathrm{a}}$ values were evaluated and compared with experimental results. In terms of three variables, ${\mathrm{k}}_{\mathrm{a}}$ can be expressed as ${\mathrm{k}}_{\mathrm{a}}=\frac{0.15 \left[\mathrm{C}{]}_{\mathrm{o}}^{-0.69} \right[\mathrm{W}{]}^{0.73}{ \mathrm{I}}^{0.91} }{1+0.17 [{\mathrm{C}]}_{\mathrm{o}} }$while the empirical model results in the following expression, ${\mathrm{k}}_{\mathrm{a}}=0.77 {\left[\mathrm{C}\right]}_{\mathrm{o}}^{-1.65} {\left[\mathrm{W}\right]}^{0.73}{ \mathrm{I}}_{\mathrm{o}}^{0.89}$. It was observed that 83.64% mineralization was achieved after a period of 16 hrs. In terms of immobilized catalyst, the DB15 degradation kinetics was described by a pseudo first-order model for different dye concentrations. Meanwhile, a power-law model described the impact of light intensity on dye kinetics. In addition, the coated catalyst was successfully reusable with high efficiency for up to four cycles.

Photocatalytic degradation of Direct Blue 15 (DB15), an azo dye, was studied using a swirl-flow monolithic reactor under UV irradiation. The degradation reactions were carried out to investigate effects of initial dye concentration, catalyst loading, and light intensity at an optimal pH. The experiments were designed and mathematically modelled by CCD-RSM (central composite design-response surface methodology) approach. It was found that the selected parameters significantly affect DB15 degradation. In terms of the linear term, catalyst loading and light intensity had a synergistic effect, while dye concentration registered the opposite effect. Strong interaction was observed between catalyst loading and both light intensity and initial dye concentration compared with the interaction of light intensity and initial dye concentration. Based on the experimental results, a quadratic model was developed to predict the percentage removal of DB15. The predicted values of the model were in good agreement with the experimental values (R² = 0.987), indicating the model fits well for the parameter space for which experiments were performed. According to diagnostic plots, the model credibility was valid because its residuals were distributed normally and exhibited a random pattern based on their examination versus the predicted values. The results revealed that the initial dye concentration and catalyst concentration have a significant effect on the mineralization time.

The importance of environmental consciousness and sustainability is increasing among transportation governing bodies worldwide. Many government bodies are concerned with maximizing the usage of recycled substances in road construction. Therefore, assessing the effect of recycled materials consumption is essential, mainly when designing new ‘green’ pavement types. The primary objective of this study is to investigate the impact of different treatments on improving the interfacial transition zone (ITZ) of coarse recycled concrete aggregate (CRCA) and its application in asphalt mixes. Such an aim is accomplished by enhancing its physical and mechanical characteristics, as well as its microstructure. The surface morphology, chemical composition, and intermix phases of the ITZ area and calcium silicate hydrate (CSH) compounds for CRCA were evaluated using scanning electron microscopy (SEM), an energy-dispersive X-ray analyzer (EDAX), and X-ray diffraction analysis (XRD). The performance of asphalt mixtures that included treated and untreated CRCA was also examined using different tests. It was found that heat treatment is an effective technique for enhancing the ITZ. However, cracks were seen in the mortar of CRCA when exposed to high temperatures (500 °C), which adversely affects the characteristics of the mortar. Acid treatment appeared to be an effective approach for improving the ITZ area. Nevertheless, the treatment that used acetic acid, a weak acid, was more effective than HCl acid, a strong acid. The outcomes revealed that the ITZ microstructure is significantly enhanced under different treatment types; however, microstructure improvements mainly included increased surface homogeneity and CSH compounds and a reduced Ca/Si ratio. It was also found that the asphalt mixtures with different proportions of untreated CRCA exhibited enhanced resistance to rutting. Furthermore, their tensile strength ratio (TSR) values were above the minimal level requirements. Moreover, the asphalt mixture with 30% CRCA, which was treated with various treatment methods, demonstrated a significant improvement in the mixtures’ mechanical properties; therefore, its application is highly successful and an environmentally friendly solution.