BACKGROUND: The capacity and mechanism of adsorption of the reactive dyes monoazo (RR2) and diazo (RR141), using a new adsorbent with a strong ecological appeal developed from the sludge of the textile effluent treatment process, were investigated. The kinetics and adsorption isotherms were determined at different temperatures and salt concentrations. After determination of the best experimental conditions for adsorption for both dyes, tests were carried out in fixed-bed adsorption columns. RESULTS: For both dyes, there was a reduction in the adsorption capacity of the adsorbent developed when the system operated at temperatures above 40 degrees C. When 10% (by mass) of sodium chloride was added to the adsorbate RR141 the maximum adsorption increased from 66.67 mg g(-1) to 78.74 mg g(-1). For both dyes, the addition of sodium sulfate did not favor significantly the adsorption. The results obtained for scale-up of the laboratory data for the adsorption columns indicated that the operating time with reactive dye diazo is 43.5% longer than that for monoazo. CONCLUSION: The adsorbent studied was shown to be a very promising alternative in terms of an environmentally friendly process. (C) 2009 Society of Chemical Industry