One-step synthesis of NaP1, SOD and ANA from a hazardous aluminum solid waste

Abstract NaP1, SOD, and ANA zeolites were synthesized from a hazardous aluminum waste as main aluminosilicate source by a one-step hydrothermal synthesis. This allowed the total transformation of the waste and no other solid residues were produced. The conversion of the waste into zeolites led to yields of ∼2.5 kg of zeolite per kg of waste. Experimental parameters such as stirring, time, temperature, and concentration of alkalizing agent (NaOH solution) were studied to determine the best synthesis conditions. Samples were characterized by different techniques such as XRD, SEM-EDS, FTIR, TG-DTA; textural properties such as BET specific surface area, zeta potential, granulometry and cation-exchange capacity (CEC) were also determined. Temperature and alkali concentration were the parameters with strongest influence in the formation of the different zeolites. Thus, the optimal conditions to obtain NaP1 and ANA were 1 M NaOH solution for 6 h at 120 and 200 °C, respectively, while SOD was prepared at 120 °C for 6 h, using a very much higher alkali concentration (5 M). These zeolites exhibited similar characteristics to those obtained from conventional chemical reagents. Besides, the mother liquor from the synthesis of NaP1 was recycled twice in order to reduce water and alkalizing agent consumption. In this case, the only crystalline phase obtained was NaP1 showing morphological, textural and crystalline characteristics very similar to those of NaP1 prepared from fresh solutions. The results show that the aluminum waste can be transformed into different types of zeolites, considered as value-added materials, with promising adsorption properties.