Adsorption of gallic acid by tailor-made magnetic metal-ceramic nanocomposites

In the last years gallic acid (GA) has been used in a growing number of industrial applications, thanks to its interesting properties. Unfortunately, the consequent presence of GA in wastewaters raises significant environmental problems. In this view, two tailor-made magnetic metal-ceramic nanocomposites, obtained from zeolite A, were developed for the adsorptive separation of GA from wastewaters. Optimized configurations of the nanocomposites, to increase their adsorption capacity and stability, were obtained by suitable modification of a patented process. The adsorption process was characterized as regards the role played by the most relevant parameters (kinetics, pH, GA concentration). The GA removal was strongly affected by pH. The experimental results suggested the interactions between GA and the nanocomposites to be based on two different mechanisms. The adsorption kinetics were in all cases described by the pseudo second-order model. The adsorption isotherms data were satisfactorily described by the Sips model, a combination of the Langmuir and Freundlich isotherm type models. Suitable conditions were found to achieve the GA desorption, as well as the recycle of the magnetic adsorbents. In this view, a procedure for the thermal regeneration of the exhausted adsorbent was developed on the basis of the TG and DTA analyses. In order to offer a more environmentally friendly approach, as well as to achieve a full recovery of the economically valuable GA, a procedure for the alkaline desorption was successfully developed. A detailed cost analysis was also carried out, showing that the specific cost for GA unit volume removal is comparable with those pertaining to alternative methods.