Introduction The textile industry has nowadays a great number of chemical products which are used as dyes in the dyeing processes; however, many of these products are toxic, and thus demand a rigorous treatment of their effluents. Biological systems of treatment, although largely utilized in the removal of color, are very inefficient, mainly for synthetic dyes of complex structures [1, 2]. Therefore, many more effective methods have been developed, such as those based on solid–liquid adsorption treatment processes. Adsorption has recently gained favor for its simplicity, low cost, and great efficiency in the removal of difficultly degradable dyes, when compared with conventional removal methods [3]. Furthermore, in some cases, it is possible to recover the dye through desorption [4]. Nowadays, diverse vegetable [1, 2] or mineral materials [3, 5, 6] are being investigated as possible low-cost adsorbents [7]. The adsorption technique has another great advantage that is related to the reuse of the large amounts of water employed by textile industries. This work presents the results of solid–liquid adsorp- tion of methylene blue as a model for the use of Barro Branco as an alternative adsorbent. Many adsorption parameters were investigated, such as the initial concen- tration of the methylene blue, the pH of the solution, temperature, and the rates of adsorption and desorption. Adsorption isotherms The Langmuir isotherm q e ¼ K L C e 1 þ a L C e ; ð1Þ Progr Colloid Polym Sci (2004) 128: 278–282 DOI 10.1007/b97109 Ó Springer-Verlag 2004 Carlos Alberto Policiano Almeida Clodoaldo Machado Nito Angelo Debacher Adsorption of methylene blue as a model for the use of Barro Branco as an alternative adsorbent for color removal C.A.P. Almeida Æ N.A. Debacher (&) Departamento de Quı´mica, Universidade Federal de Santa Catarina, 88040-900 Floriano´polis, SC, Brazil e-mail: debacher@qmc.ufsc.br C. Machado Departamento de Quı´mica, Universidade Regional de Blumenau, CEP 89010-971, SC, Brazil Abstract The application of the solid–liquid adsorption technique with low-cost adsorbents has been offering promising results in the treatment of textile wastewaters. In this study, we used as an adsorbent Barro Branco (aluminum-silicate – Al 16.2%, Si 21.5% and O 44.77%), one of the main by-products of the extraction of mineral coal. The samples were obtained at the Espe- ranc¸a mine, Santa Catarina, Brazil. The experiments were carried out in an adsorber vessel with controlled temperature, pH and a mechanical stirrer. A 1.0 g sample of Barro Branco (210–297 lm) was added to each 50 cm 3 of methylene blue dye solution. The results show that Bar- ro Branco is a promising adsorbent for color removal, where the adsorption kinetics fit better to the pseudo-first-order rate law. The val- ues of the rate constant of the adsorption decreased with the increase of the concentration. The isotherm constants agree well with the Langmuir equation and the Freundlich equation, with correla- tion coefficients close to 1.00 in both cases. Keywords Methylene blue Æ Adsorption Æ Barro Branco Æ Langmuir isotherm Æ Freundlich isotherms