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 cm3/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...