: As a recycled material, flue gas desulfurization gypsum has been used to prepare calcium sulfate hemihydrate whisker (CSHW) through hydrothermal synthesis for several decades. However, the subsequent utilization of this resultant material has not yet received considerable attention. In the present research, CSHW was successfully synthesized at a certain region, and was used for the adsorption of lead ions from aqueous solutions, thereby broadening the research field for the practical application of CSHW. Its adsorption capacity was significantly influenced by various parameters, particularly, the pH level and initial lead concentration. The pH value highly affected the hydrolysis degree of lead ions and dominated the adsorption of lead. The equilibrium isotherms under two different temperatures were simulated using Langmuir, Freundlich, and Temkin models. Both Langmuir and Temkin models showed a good fit to the data. Combined with the well-fitted pseudo-second-order model, the adsorption mechanism was thought to be a chemisorption process that was enforced by the ion exchange reaction. In addition, the specific crystal structure of CSHW revealed that ion exchange reaction occurred on the (010) and (100) facets due to their preferential growth and negatively charged property. The residual solid phase after adsorption was collected and detected using X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. Results revealed that PbSO₄ was formed on the surface of CSHW. The alkaline condition introduced the tribasic lead sulfate, and thus reduced the stability of the adsorption system.

In this work, the thermal behavior of rice husk, sewage sludge, and their blends during combustion processes was investigated by means of thermogravimetric analysis (TGA), and the slagging characteristics were studied through X-ray fluorescence (XRF) and melting temperature. The effects of the proportion of rice husk and sewage sludge blends on the combustion process, ignition and burnout characteristics were also studied. The blends had rice husk percentages of 30, 50, 70 and 100%. The results indicate that there are four main stages of the material burning processes: dehydration, volatile oxidation, and decomposition/oxidation. The reactivity of the blends improved with increasing amounts of rice husk and the results suggest synergistic interactions between rice husk and sewage sludge during the co-combustion process. All co-combustion ashes showed a lower slagging potential owing to their high amorphous SiO₂ content. On the basis of combustion properties and slagging characteristics of ash, the ratio of sewage sludge in the blends should not exceed 30%.

The study aims to determine the adsorption mechanism of reactive brilliant red X-3B (RBR) on a novel low-cost clay–biochar composite with different proportions of bagasse and natural attapulgite (ATP). Pure bagasse, pure ATP, and two mixtures with weight ratios of 1:5 and 1:3 were pyrolyzed at 700 °C for 4 h in a muffle furnace. Biochar samples were characterized with an element analyzer and by scanning electron microscopy, X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller method, and zeta potential measurement. Results of the batch and leaching experiments showed that the adsorption capacities followed the order of 1:3 clay–biochar > 1:5 clay–biochar > bagasse biochar > pure ATP. Furthermore, ATP and bagasse exerted a synergistic effect on the adsorption of RBR. The adsorption data showed good correlation with the Langmuir isotherm, and the kinetic data were fitted to the pseudo-second-order model. The adsorption of RBR on clay-biochar involved electrostatic interaction, hydrogen bond, π–π interactions, and surface participation. The modification of biochar by ATP improved the adsorption capacity by increasing functional groups and creating adsorption sites. Therefore, ATP-modified clay–biochar composites could be effective adsorbents for the removal of RBR from wastewater.