Lignin-Based Activated Carbons as Adsorbents For Crystal Violet Removal from Aqueous Solutions Luis M. Cotoruelo, a Marı´a D. Marque ´ s, a Francisco J. Dı ´az, a Jose ´ Rodrı ´guez-Mirasol, a Juan J. Rodrı´guez, b and Toma ´ s Cordero a a Departamento de Ingenierı´a Quı´mica, Facultad de Ciencias, Universidad de Ma ´laga, 29071 Ma ´laga, Espan ˜ a; lcot@uma.es (for correspondence) b Ingenierı´a Quı´mica, Facultad de Ciencias, Universidad Auto ´noma de Madrid, 28049 Madrid, Espan ˜a Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.10560 The adsorption of crystal violet (CV) from its aque- ous solutions has been studied using eight activated carbons (ACs) prepared from eucalyptus kraft lignin. The adsorption isotherms were fitted to the Langmuir model. Amounts adsorbed in the range from 110 to 600 mg CV cation/g AC were studied as a function of the operating variables (pH, temperature) as well as the properties (burn off, porosity) of the ACs. The ther- modynamic values involved endothermic processes. The kinetic study showed that the processes are of 2nd apparent order related to the concentrations of the vacant active sites on the ACs surface. The low values of the effective diffusivities suggested internal diffusion control on the net mass transfer. The results obtained in the present work can be of utility in the preparation of new adsorbents as well as to design the adsorption equipment for the removal of CV from waters with environmental purposes. Ó 2011 American Institute of Chemical Engineers Environ Prog, 00: 000–000, 2011 Keywords: cationic dye, residual biomass, adsorp- tion, thermodynamics, kinetics INTRODUCTION Most of the dyes used in industry are stable to the light and oxidation as well as resistant to the aerobic digestion, causing damage to the aquatic life. The presence of very small amounts of dyes in water (less than 1 ppm for some dyes) is highly visible and undesirable. The aim of this work has been to study the adsorption of a basic dye, crystal violet (CV) (also known as gentian violet, methyl violet 10B, and basic violet 3) from its aqueous solutions. The cati- onic dye has been chosen because of its great industrial importance derived from its numerous uses in the chemical business and its effects into the aquatic environment [1]. Hence the dye removal from waters becomes essential. Numerous authors have studied the crystal violet adsorption on many adsorbent systems including silica, alumina, perlite, different waste materials, and various types of acti- vated carbons [1–11]. The thermochemical conversion of lignocellulosic wastes has gained attention in the last decades. Lig- nin is one of the three basic components of wood, where it ranges commonly between 20% and 30%. A modified type of lignin, the kraft lignin, represents a major by-product of the cellulose-pulp industry. Dur- ing the kraft process, chemical breakage and solubili- zation of polymeric lignin is achieved giving rise to a waste black liquor which is commonly evaporated and calcinated to recover energy and chemical reac- tant. Among other considerations of chemical and environmental concern, the possibility of alternative ways for black liquors processing gives to the plant Ó 2011 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2011 1