Purification of Alkaline Solutions from Dyes by Microfiltration Ceramic Membranes Made of Clay Minerals Modified by Montmorillonite

We determined the physicochemical regularities of the process of purification of an alkaline solution of a cationic dye (Methylene Blue) and anionic dyes (Direct Brown and Direct Red) using a microfiltration ceramic membrane based on clay minerals, which is dynamically modified with montmorillonite. This membrane retained 99.6% of Methylene Blue at specific productivity of 0.08 m3/(m2 h) at an initial concentration of the dye of 50 mg/dm3, pH0 12.5, P 1.0 MPa, and a permeate selection factor of 80%. The high retention capacity of the ceramic membrane to Methylene Blue is due to the presence of a modifying layer of montmorillonite on its surface, ensuring the adsorption of dyes in the form of an additional retention gel-like layer of dye associates. The modified microfiltration ceramic membranes made of clay minerals, developed at the Dumansky Institute of Colloidal Chemistry and Water Chemistry, National Academy of Sciences of Ukraine, are comparable to modified microfiltration membranes of oxide ceramics from Rauschert (Germany) in the efficiency of water purification from cationic dyes but are much more productive and cheaper than the latter. Under similar conditions, the modified membrane of clay minerals also showed a high retention capacity to Direct Brown and Direct Red anionic dyes. The mechanism of their retention is associated with the electrostatic repulsion of like-charged anions of dyes and montmorillonite particles. A clay-based ceramic membrane modified with montmorillonite is proposed for the pretreatment of alkaline washing solutions of banknote factories.