Wood and Mineral Byproducts Soft Activated as Adsorbents to Liquid-Phase Application

Abstract

Human activities generate byproducts and wastes that need to be valorised. This paper presents a comparative study on the valorisation of different natural byproducts, of vegetal and mineral origin, through their transformation into adsorbent materials. A series of byproducts (European wood pellets, African natural woods, natural charcoal, lignocellulosic ash, perlite and vermiculite minerals and expanded clay), as received and after smooth activation processes, were tested for adsorption from liquid phase. The aqueous phase tests were carried out with representative molecules from several classes of hazardous compounds such as dyes, pesticides and pharmaceuticals. The molecules selected were methylene blue (MB), acid yellow 17 (AY 17), (4-chloro-2-methyl-phenoxy) acetic acid (MCPA), 4-nitrophenol (4N) and sodium diclofenac (SD). The results obtained with this set of natural, alternative and non-conventional low-cost adsorbents were interesting, particularly in the case of adsorbents of vegetal origin, natural woods and also in the case of lignocellulosic ash. Regarding the soft chemical modification, it has been shown to be a process that allows the preparation of materials with improved performance for some adsorptive/adsorbent systems, namely natural woods/(AY 17; MB; 4N) and natural charcoal and lignocellulosic ash/all the adsorptives. Note that the adsorption processes were relatively fast, with an equilibrium time of around 24 h. In conclusion, the byproducts analysed, some of them after soft activation, present a potential for valorisation through their use as adsorbents for hazardous polluting compounds from the aqueous medium at a temperature of 25 °C.