Preparation of a New Granular Acid-Activated Neutralized Red Mud and Evaluation of Its Performance for Phosphate Adsorption

A new granular acid-activated neutralized red mud (AaN-RM) was successfully prepared with powdered AaN-RM, powdered straw, and hydroxypropyl methylcellulose (HPMC) for effective phosphate adsorption. The maximum phosphate adsorption capacity of granular AaN-RM reached 86.69 mg/g, which was much higher than that previously reported. Its excellent phosphate adsorption capacity was mainly attributed to high specific surface area caused by complex mineralogy of iron and aluminum and addition of powdered straw. The mass ratio of different ingredients, sintering temperature, and time affected the characteristics of granular AaN-RM greatly. When the mass ratio of powdered straw increased from zero to 33%, the total pore volume of granular AaN-RM increased from 0.0056 to 0.0375 cm(3)/g; however, the effective chemical compositions reduced when the addition of powdered straw was too high. With increasing the sintering temperature and time, the polymerizability of granular AaN-RM was significantly improved, but a too high sintering temperature and too long sintering time resulted in the conversion of part FeCl3 center dot 2H(2)O to FeOCl and FeCl2 and part Al(OH)(3) to Al2O3, leading to a weaker attraction for phosphate. The optimal mass ratio of powdered AaN-RM, powdered straw, and HPMC was 71:22:7; the sintering temperature and time were 225 degrees C and 30 min, respectively.