Silicates as Binders in the Preparation of Adsorbent Materials ^†

The use of binders in the preparation of materials for a wide range of applications is a well-known practice. In this work, we explore the use of silicates as binders to aggregate carbon materials for applications as adsorbents, Figure 1. A set of binders of the family of silicates, among them sodium silicate and some commercial silicates (LUDOX^® AS-40, Ludox^® AM and Ludox^® TMA), were used in the agglomeration of a commercial adsorbent (Activated Carbon-AC) by direct spray dispersion and a rotary technique. The best agglomeration conditions obtained with AC were replicated with a non-commercial carbon adsorbent of a lignocellulosic nature prepared in our laboratory. Selected samples were also submitted to thermal treatment (in a non-controlled atmosphere and inert atmosphere), and physical activation with carbon dioxide (CO₂) aimed to increase grain stability and improve the adsorptive properties of the samples, namely their surface chemistry and porosity.

The samples with a higher mechanical stability and better structural and chemical properties were used in the adsorption of toxic substances in liquid phase, namely arsenic. In these aqueous-phase adsorption experiments, parameters such as agitation, temperature, pH, concentration of the adsorptive, and kinetic aspects were evaluated. A first cost analysis of the process will be also presented.

This work shows how silicate solutions, with an initial concentration ranging from 10 to ~30%, could be employed as binders to granulate carbon materials adsorbents for use on batch and fixed-bed column adsorption systems. Furthermore, this work follows a circular economy approach based on the use of adsorbent materials of natural and renewable origin, particularly lignocellulosic waste and environmentally friendly binders, such as silicates, aiming to prepare an added-value material with potential applications in the treatment of drinking water and wastewater.