Adsorption of Phosphate in Aqueous Solutions Using Manganese Dioxide

Effort to remove phosphate from aquatic ecosystem is of great interest, not only for preventing algae bloom problem but also for recovering phosphate, as this is an essential material. Adsorption is considered as an effective method especially because the nutrient loaded adsorbent can be directly used for fertilizer. Therefore, this study investigated the potential use of manganese dioxide in natural form (pyrolusite) to adsorb phosphate in aqueous solutions. A series of batch experiments were done to elaborate the adsorption process of phosphate onto manganese dioxide. Several environmental conditions such as pH, temperature and ionic strength were applied in order to get a better understanding of the process mechanism. The results indicated that pH was obviously affected the adsorption process, meanwhile ionic strength did not play significant role. The adsorption of phosphate was higher at a lower pH and getting reduced as the pH increased. Similar to that, the percentage removal of phosphate was declined significantly in higher ionic strength, indicated that the interaction between phosphate and manganese dioxide was mainly controlled by electrostatic force. The adsorption isotherm data correlated better with Langmuir model rather than Freundlich model. The maximum adsorption capacity of manganese dioxide was 11.40 mg P/g. The kinetic data was very well fitted to pseudo second order equation suggested that chemical reaction involved in adsorption process. Moreover, thermodynamic data confirmed that phosphate adsorption onto manganese dioxide was an endothermic process.