Mitigating the Environmental Impact by Synthesis of Adsorbents from Aluminium-Containing Waste

Purpose: To develop effective adsorbents and carriers for removing harmful impurities from waste, due to the shortage of natural bauxite for alumina production. Methods: To determine the influence of various impurities present in the waste—spent alumina adsorbent (SAA) on the characteristics of adsorbents for chlorine-containing compounds, samples with a different content of V, Ti and Na have been synthesized. Properties of adsorbents based on a commercial alumina and extensively treated SAA, both types undergoing impregnation with sodium hydroxide and sodium vanadate, have been compared. Alumina adsorbents and alumina-kaolin-borate catalyst carriers with the Ti content of ca. 0.2% were prepared by atomic layer deposition (ALD) of TiCl₄ on the ready granules, while introduction of large quantities of titania have been performed by addition of ground alumina-titania carrier waste into the extrusion paste. Adsorption of steam, tetrachloroethylene and hydrochloric acid has been investigated. Results and Conclusions: It was found that the adsorption capacity for water vapor reached 43.6 g H₂O/100 g SA and 38.9 g H₂O/100 g AN-2, while after ALD modification it decreased by ca. 1 and 35%, respectively and with the introduction of SA-Ti(15.0) with the same amount of titanium by ca. 35%. Modification of AN-2 with sodium vanadate at about 0.3% Na and 0.4% V had no effect on water adsorption; while as the concentration of sodium introduced by impregnation with NaOH increased, the adsorption ability deteriorated. Modification of AN-2 and SA using ALD technology sharply diminished efficiency of adsorption of water vapors, tetrachlorethylene and hydrochloric acid. By adsorption of a mixture simulating reforming exhaust gases, formation of chlorinated oligomers on AKB, AN-2 and SA was established. NaOH modification effectively suppressed oligomerization; thus SAA-based adsorbents containing more than 5% Na can be used for drying and purification of reforming exhaust gases, as the most effective, cheapest and resource-saving option. Graphical Abstract: (Figure presented.)