<p>In this study, the molecular adsorption mechanism of methylene blue dye on ulexite and the adsorption kinetics and thermodynamics were investigated. Ulexite is a boron mineral containing boron, sodium and calcium. The regression coefficients of Langmuir isotherm, Freundlich isotherm and Dubinin-Radushkevich (DR) isotherms were compared. Adsorption of methylene blue on to ulexite was investigated thermodynamically. The most appropriate kinetic model was determined using pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The molecular adsorption mechanism of methylene blue on ulexite was schematically explained. The adsorption results showed that maximum adsorption capacity obtained from DR isotherm model was 1180&#xa0;mg/g. When compared with studies in the literature, this maximum adsorption capacity was found to be very high. Methylene blue was successfully separated from aqueous solutions with very high adsorption capacity using ulexite.</p>