Application of Industrial Wastes from Chemically Treated Aluminum Saline Slags as Adsorbents

Abstract

In this study, industrial wastes, which remain after aluminum extraction from saline slags, were used as adsorbents. The aluminum saline slags were treated under reflux with 2 mol/dm 3 aqueous solutions of NaOH, H 2 SO 4 , and HCl for 2 h. After separation by filtration, aqueous solutions containing the extracted aluminum and residual wastes were obtained. The wastes were characterized by nitrogen adsorption at −196 °C, X-ray diffraction, scanning electron microscopy, and ammonia pulse chemisorption. The chemical treatment reduced the specific surface area, from 84 to 23 m 2 /g, and the pore volume, from 0.136 to 0.052 cm 3 /g, of the saline slag and increased the ammonia-adsorption capacity from 2.84 to 5.22 cm 3 /g, in the case of acid-treated solids. The materials were applied for the removal of Acid Orange 7 and Acid Blue 80 from aqueous solutions, considering both single and binary systems. The results showed interesting differences in the adsorption capacity between the samples. The saline slag treated with HCl rapidly adsorbed all of the dyes present in solution, whereas the other materials retained between 50 and 70% of the molecules present in solution. The amount of Acid Orange 7 removed by the nontreated material and by the material treated with NaOH increased in the presence of Acid Blue 80, which can be considered as a synergistic behavior. The CO 2 adsorption of the solids at several temperatures up to 200 °C was also evaluated under dry conditions. The aluminum saline slag presented an adsorption capacity higher than the rest of treated samples, a behavior that can be explained by the specific sites of adsorption and the textural properties of the solids. The isosteric heats of CO 2 adsorption, determined from the Clausius–Clapeyron equation, varied between 1.7 and 26.8 kJ/mol. The wastes should be used as adsorbents for the selective removal of organic contaminants in wastewater treatment.

Efficient recovery of aluminum from saline slag wastes

“…No other compounds or elements were detected in any of the samples characterized. They may be in the form of amorphous phases or also as crystalline phases but in very low amounts, in both cases not detectable by XRD [7].…”

“…The starting point and reference conditions for this study come from the experience of our research group [7] about alkaline extraction of Al from aluminum saline slags: 37.5 g of hazardous waste is treated under reflux and stirring with 0.75 cm 3 of 2 mol/dm 3 aqueous solution of NaOH for 2 h. So, the ratio waste/NaOH is 1:20 g/dm 3 .…”

“…Potential applications for aluminum saline slags as a raw material are being studied in the last years in construction, polymer composites, adsorbents or salts but another interesting strategy is to solve the available Al and use to synthesize useful materials [3,4]. Our research group have published various studies about aluminum salts valorization and it applications to synthesize several materials as pure alumina, salts, hydroxides and hydrotalcites [2,[5][6][7].…”

“…Previous studies carried out by other authors use a single stage to extract aluminum [8][9][10][11][12][13], leaving more aluminum in the residue that could be extracted and used. The treatment performed removes the toxic compounds from the saline slag to become a nonhazardous waste that can be handle as by-product [7]. As a second objective, the study included the extraction of aluminum from the waste to synthetize other materials with added value as hydrotalcites, among others [6,14].…”

Preparation of Pollucite and Analcime Zeolites as a Method to Valorize Aluminum Saline Slags

“…Raw saline slag contains various aluminum species (metallic Al, Al(OH)3, different phases of Al2O3, etc.) forming aggregates of different sizes and can be managed in different ways [2,[6][7][8][9][10].…”