This article considers an effective way of complex alumina-containing materials of natural or technogenic origin processing with obtaining a whole complex of raw materials: alkali-free highly active aluminum hydroxide, iron hydroxide, aluminum hydroxide, etc. In laboratory conditions the alumina raw materials behavior in the thickening, washing, filtration processes were checked. The optimal parameters of the processes were selected as a result of conducted research.
Keywords: non-conventional alumina raw materials, technogenic materials, hydrochemical processing, ammonium hydrosulfate, environmental friendliness, efficiency
Cu-ZSM-5 and Ce-doped Cu-Ce-ZSM-5 samples were prepared by liquid-phase ion exchange method. The two catalysts were subjected to hydrothermal aging treatment in the simulated flue gas of a coal-fired power station at an ageing temperature of 650–850 °C. The denitration experiment found that the activity of the aged Cu-ZSM-5 was 19.6% to 41% lower than that of the fresh Cu-ZSM-5 at the optimal decomposition temperature of NO at 550 °C, while the aged Cu-Ce-ZSM-5 had only a 14.8% to 31.5% reduction in activity than the fresh Cu-Ce-ZSM-5. The samples were characterized by XRD, BET, H2-TPR, XPS, NO-TPD, etc. The results showed that hydrothermal aging treatment leads to the dealumination of the ZSM-5 framework and reduces the specific surface area and pore volume of the micropore in the sample. It also exacerbates the isolated Cu2+, and the active center {Cu2+-O2−-Cu2+}2+ dimers migrate towards the sample surface and form inactive CuO. Doping with Ce can promote the dispersion of Cu(OH)+, which was the precursor of {Cu2+-O2−-Cu2+}2+. Ce3+ can preferentially occupy the less active bridged hydroxyl exchange sites, so that copper ions occupy the more active aluminum hydroxyl sites, thereby inhibiting the migration of active centers.
Active metal pigments in metal-rich coatings are oxidized preferentially and provide sacrificial protection to more-noble metallic substrates. Al-rich primer (AlRP), which contains pigment particles made from an active aluminum alloy (Al-5Zn-0.02In), uses this mechanism to provide a chromate-free epoxy primer system. To address the high self-corrosion rate of active aluminum pigments, the active aluminum pigment particles are pretreated using trivalent chromium process (TCP). In this study, the effects of different TCP treatment times were evaluated, and coating protection properties were studied. Potentiodynamic polarization tests were performed in aerated 0.1 M NaCl solution for a TCP-treated bulk active aluminum alloy and for AA2024-T3. The potentiodynamic polarization curves show that the corrosion potential of the bulk active aluminum alloy is about 500 mV lower than that of AA2024-T3. Therefore, bulk active aluminum alloy is a candidate alloy for cathodic protection of AA2024-T3. In addition, the TCP treatment reduces the corrosion rate of the bulk active aluminum alloy by one order of magnitude. AlRP-coated AA2024-T3 panel samples were scribed and exposed in corrosion chambers, and the cross section of each coating was evaluated by scanning electron microscopy and energy dispersive x-ray spectroscopy mapping. The accelerated corrosion exposure results show that AlRP coatings containing TCP-treated particles provided better protection to the scribe than the one with bare pigment particles. The adhesion of the AlRPs based on pull-off adhesion tests was similar regardless of the TCP treatment time of the pigments, but the adhesion of AlRP was reduced in comparison to a neat epoxy coating.
The process for preparation of active aluminum hydroxyoxide via flash calcination of gibbsite in a new energy-efficient centrifugal drum-type reactor