Research On Red Mud's Performance And Mechanism Of Phosphate Adsorption

Red mud is a solid waste copiously emerging during the alkaline leaching process in aluminum industry. Based on its particular surface characters and high concentration of Fe, Ca and Al, red mud is considered as a potential adsorbent. In this study, red mud from calcination method (RMC) and bayer process (RMt,) were employed as basic materials and the corresponding acidified samples were signed as RMca and RMba-Those four kinds of samples were used as adsorbent for phosphate removal and the results were listed as following:(1) In acidification, the effect of acid concentration was significant. With the effect of hydrochloric acid, the alkaline groups on original material were partialy dissolved, which weakened the alkalinity, increased the coarseness of surface and changed the corresponding quality of each phase of material;(2) The initial pH value (pHi) was considered to be the most significant factor. The optimal condition in this study was pHi=2, under this condition the phosphate removal efficiency of the acidified samples were better than that of original samples. Especially when Ci=30mg/L, the phosphate removal efficiency of RMca almost approached 100%. It's worth to mention that using RMC as adsorbent, the pHr of water was around 7.0, which was positive for practice use;(3) The results of adsorption kinetic experiments of each sample have high relativity with pseudo second kinetic models. This implied the main adsorbtion mechanism of samples was the chemisorption or chemical binding caused by valency forces. This also implied the Fe, Ca and Al contained in red mud determined red mud's adsorption efficiency;(4) By comparing the Langmuir and Freundlich isotherm models, the latter one was considered to describe the data of each sample better and emphasize the importance of heterogeneous adsorption. Furthermore, there wasn't significant reletivity between samples' data and Dubinin Radushkevin isotherm model, which implied that the adsorption of samples were not determined by temprature.The core purpose of this study is to supply basic data and theory for realizing the objective of using red mud in phosphate removal from water.