A new method has been developed to reduce the concentration of Ferric ions present as inorganic impurities in crude Egyptian phosphoric acid. This method is based on the silica extracted by alkaline treatment of rice husk to carry out the exchange of ions. Several parameters (contact time, temperature, sorbent type, sorbent mass, and batch factor) were examined. Simultaneous determination of Fe3+ ions in presence of uranium ions before and after treatment revealed that the concentration of uranium was reduced by similar to18% during the removal of Fe3+. Adsorption isotherm indicates that the monolayer coverage is 0.386 g Fe3+ ions per g sorbent. In dynamic mode, the adsorption capacity at (C-e/C-o = 50% or Q(0.5)) was = 22.5 mg/g and the column recycled at least three times and only needs 150 ml of 0.1 M HNO3 for each regeneration and no weight loss in sorbent per cycle should be considered. Therefore, the developed rice husk adsorbent is considered as a better replacement technology for removal of Fe3+ ions due to its low cost and good efficiency in this application. The cost of 1 kg of the modified rice husk (MRH) is estimated and the sorption mechanism is discussed. (C) 2003 Elsevier B.V. All rights reserved.