Hydrotalcite and hydrocalumite as resources from waste materials of concrete aggregate and Al-dross by microwave-hydrothermal process

Preparation and Adsorption Properties of Soybean Dreg/Hydrocalumite Composites

The application of biomass-based composites in the field of adsorption has attracted extensive attention. Herein, soybean dreg/hydrocalumite composites were prepared by in situ self-assembly from soybean dregs and applied to the adsorption of Congo Red (CR). The composites were characterized by scanning electron microscopy, X-ray diffraction, Fourier infrared spectroscopy, and N₂ physical adsorption-desorption. The results showed that the adsorption property of soybean dregs/hydrocalumite for CR was better than that of soybean dregs or hydrocalumite. Effects of preparation and adsorption conditions on the adsorption of CR by soybean dregs/hydrocalumite were also investigated. The removal rate of soybean dregs/hydrocalumite (30%BD-LDH) prepared under the optimized conditions reached 97.4% with a 486.8 mg·g^-1 adsorption capacity. Also, the adsorption capacity of 30%BD-LDH was about 2.4 times and 3.0 times that of hydrocalumite and soybean dregs, respectively. In addition, the adsorption process of CR by 30%BD-LDH was more in line with the pseudo-second-order kinetic and Langmuir isothermal models.

Reduction for heavy metals in pickling sludge with aluminum nitride in secondary aluminum dross by pyrometallurgy, followed by glass ceramics manufacture

Secondary aluminum dross (SAD) from aluminum industry is classified as a hazardous solid waste due to containing aluminum nitride (AlN). In this work, AlN was first used to reduce heavy metals by pyrometallurgy. The reduction rates for iron, chromium and nickel were up to 90%, 80% and 100%, respectively. However, the reduction from AlN and oxygen oxidization of AlN occurred simultaneously. AlN which formed solid solution with alumina could reduce heavy metals, while the rest was oxidized by oxygen. In addition, the reduction rates for iron and chromium could be increased with increasing CaF₂ from 6.7 to 9.0 wt%. CaF₂ could decreased viscosity of molten slag, which favored the ion migration, and then increased the reduction rates. After the reduction, glass ceramics were manufactured from the molten slags. The bending strength, microhardness and alkali resistance of the glass ceramics were up to 77 MPa, 1011 HV and 98.7%, respectively. According to XRD and SEM results, glass ceramics with CaAl₂SiO₆ crystal phase, crosslinked network structure grains and smaller pores exhibited better bending resistance. In addition, glass ceramics with CaAl₂SiO₆ crystal phase possessed the highest microhardness and alkali resistance. After this process, hazardous pickling sludge and SAD were totally recycled.

Green Synthesis of Hydrocalumite (CaAl-OH-LDH) from Ca(OH)2 and Al(OH)3 and the Parameters That Influence Its Formation and Speciation

Hydrocalumite is a layered double hydroxide (LDH) that is finding increased application in numerous scientific fields. Typically, this material is produced through environmentally polluting methods such as co-precipitation, sol-gel synthesis and urea-hydrolysis. Here, the hydrothermal green (environmentally friendly) synthesis of hydrocalumite (CaAl-OH) from Ca(OH)2 and Al(OH)3 in water and the parameters that influence its formation are discussed. The parameters investigated include the reaction temperature, reaction time, molar calcium-to-aluminium ratio, the morphology/crystallinity of reactants used, mixing and the water-to-solids ratio. Hydrocalumite formation was favoured in all experiments, making up between approximately 50% and 85% of the final crystalline phases obtained. Factors that were found to encourage higher hydrocalumite purity include a low water-to-solids ratio, an increase in the reaction time, sufficient mixing, the use of amorphous Al(OH)3 with a high surface area, reaction at an adequate temperature and, most surprisingly, the use of a calcium-to-aluminium ratio that stoichiometrically favours katoite formation. X-ray diffraction (XRD) and Rietveld refinement were used to determine the composition and crystal structures of the materials formed. Scanning electron microscopy (SEM) was used to determine morphological differences and Fourier-transform infrared analysis with attenuated total reflectance (FTIR-ATR) was used to identify possible carbonate contamination, inter alia. While the synthesis was conducted in an inert environment, some carbonate contamination could not be avoided. A thorough discussion on the topic of carbonate contamination in the hydrothermal synthesis of hydrocalumite was given, and the route to improved conversion as well as the possible reaction pathway were discussed.

The improved treatment of liquid crystals into non-hazardous molecules using a microwave-assisted hydrothermal method

Liquid crystal (LC), as a crucial component of liquid crystal display (LCD), improperly treatment of which will possibly impair ecosystems and human health. In view of the advantages of hydrothermal reaction and microwave irradiation, this paper intensively studied the process of microwave-assisted hydrothermal (MWAH) decomposition of LC wastes. The experimental materials include a kind of refractory fluorinated liquid crystal commonly used in thin-film transistor LCD, and its mixture with the other two typical liquid crystal monomers in the waste low-end display panels. Under the MWAH process, the optimized condition for thorough decomposition of 0.67 g.L^-1 fluorinated liquid crystal is 0.653 mol.L^-1 H₂O₂, 1 g.L^-1 AC, 300 mL water, 250 °C and 7 min. The superiority of microwave in enhancing hydrothermal treatment efficiency was verified by the first-order kinetic reaction equation fitted for the decomposition process under optimal condition, along with two possible decomposition pathways tentatively proposed after characterizing the intermediate products. Under the same condition, 1 g.L^-1 mixture of fluorinated liquid crystal and the other two liquid crystal monomers were entirely decomposed with no harmful byproduct detected, suggesting that microwave irradiation could effectively promote the hydrothermal decomposition of liquid crystal wastes.