Abstract—The effect of activation and heat treatment of row red mud (a residue from bauxite refining) on the adsorption of phosphate (PO 4 -P) from its solutions was studied in parallel experiments. Effect of time, temperature, concentration of adsorbate was studied using batch experiments. The adsorption of phosphate follows Langmuir better than Freundlich adsorption isotherm. Reprecipitated and calcined red mud was found to be the most efficient activation processes for the raw red mud. These findings can be extended to the treatment of industrial effluents containing phosphates like that from phosphatic fertilizer plants. Index Terms—Adsorption, red mud, PO 4 -P, wastewaters. I. INTRODUCTION Red mud is an insoluble residue produced when refining of bauxite to finally obtain pure aluminum. Red mud, due to its high aluminum, iron, and calcium content, has been suggested as a cheap adsorbent for removal of toxic metals (e.g., As, Cr, Pb, Cd) as well as for water or wastewater treatment. The basic advantage of red mud is its versatility in application. Since it is composed of a mixture of useful adsorbents and flocculants, it can be used for treatment of several effluents [1] Phosphates and nitrates are usually added to the soil in the form of fertilizers to enhance plant growth. Large concentrations of these anions in wastewaters are considered as a great hazard to human beings, they also contribute to high BOD levels that they cause plant life and algae to grow quickly in different waters. When algae grow quickly, they also die quickly. This contributes to the organic waste in the water, which is then decomposed by bacteria and then dissolved oxygen (DO) levels decrease. Since less dissolved oxygen is available in the water, fish and other aquatic organisms may not survive. In order to eliminate the possible dangers to receiving water sources, it is necessary to treat before discharge. Adsorption of phosphate from aqueous solution has been studied in the past few decades by several authors using different adsorbents, like activated alumina [2], half-burnt dolomite [3], activated carbon [4,5], coconut shell carbon [6], clays [7], bentonite [8], ferrihydrite [9], goethite [10], and hematite [11]. Manuscript received April 25, 2012; revised July 5, 2012. Ahmed M. Yousif is with the Department of Chemistry, Faculty of Science, Minufiya University, Egypt (e-mail: amm_yousif_000@ hotmail.com). Michael Rodgers is with Civil Engineering, National University of Ireland, Galway, Ireland (e-mail: Michael.rodgers@nugalway.ie). Eoghan Clifford is with Civil Engineering, National University of Ireland, Galway, Ireland (e-mail: eoghan.clifford@nugalway.ie). In recent years, considerable attention has been paid based on economic and environmental concerns to the study of using red mud (RM) [12,13] as alternative adsorbents for sorption of phosphate from water. In the present paper, removal of phosphate from aqueous solution using the raw RM and its active forms prepared by different chemical and thermal methods were studied in batch equilibration technique. The influences of time and initial phosphate concentration on the sorption capacity were investigated. The isotherm sorption experiments were also conducted. II. EXPERIMENTAL A. Materials Raw red mud (RM) samples used in the present study were obtained from bauxite refining factories, Ireland. RM was activated with different procedures as will be described in the following section. K 2 HPO 4 is used as a source of PO 4 -P. All the other used chemicals are Aldrich products. B. Textural Properties of Red Mud Particle size analysis was performed by using different sieves with different diameters (5, 3.36, 2, 1.18, 1 mm) and (600, 425, 300, 250, 150, 63 μm) and the results were listed in Table I. C. Activation of Washed Red Mud 1) By calcination Washed red mud samples placed in porcelain dishes were heat-treated at 700 o C for 2 hours in an oven. The powder was stirred once during the heat treatment. It is a fact that the optimum conditions of temperature and time for the calcinations process to remove PO 4 -P from its solutions are 700 o C and 2 hours, respectively [14]. If we calcine red mud at lower temperature or time, the surface area will be comparatively less, also it will be less efficient as temperatures are increased or time is prolonged. That is because of the decomposition of some hydroxyl groups and the shrinkage of materials. 2) By adding additives Because of the high sodium content and alkalinity of the red mud [13], we treated the red mud with adding 8% (w/w) anhydrous CaSO 4 to each of raw and calcined red mud in order to: i) reduce the pH to nearly pH 8 at solid/water ratio of 1:2.5 (the most desired pH for PO 4 -P adsorption on red mud as will be discussed later on). ii) to make probable calcium sulphate complex which is preferable also at this range of pH. 3) By reprecipitation of dissolved red mud Procedure was described by Kerry C. et al [15] by Studying the Adsorption Properties of Modified Red Mud towards Phosphate Removal from its Solutions Ahmed M. Yousif, Michael Rodgers, and Eoghan Clifford International Journal of Environmental Science and Development, Vol. 3, No. 4, August 2012 354