Statistically designed experiments were done to study the recovery of Mg content from natural smectite clays from Serbia by hydrochloric acid leaching. The effects of relevant factors, such as temperature, leaching time, acid normality, solid-to-liquid ratio and stirring rate on leaching yield of MgO have been investigated. Experiments have been planned by the factorial design method. To test the significance of the effects, an analysis of variance has been conducted at 95% confidence intervals. The structural and adsorption properties of the starting smectite clay and the sample activated at chosen conditions were investigated by means of a model. Scanning electron microscopy (SEM) and nitrogen adsorption-desorption were used to analyze the morphological characteristic of the starting and the activated sample. The results from the nitrogen adsorption-desorption isotherms show that the activated smectite clay possess a narrow pore size distribution of about 2 nm, and a large specific surface area of 238 m(2)/g. The results of X-ray diffraction (XRD) and infrared analysis (IR) of starting and activated samples confirmed that smectite was the dominant mineral phase. Besides, chemical treatment of smectite clay with HCl produces an adsorbent with optimal porosity and other adsorption properties suitable for many industrial processes. (C) 2007 Elsevier B.V. All rights reserved.