Adsorption of inorganic and organic phosphorus onto polypyrrole modified red mud: Evidence from batch and column experiments

The ubiquitous presence of inorganic and organic phosphorus in wastewater and natural water bodies has deteriorated the water environment qualities and exerted significant influences on ecosystems. In this study, an effective polypyrrole modified red mud adsorbent (PRM) was optimized for the adsorptive removal of inorganic and organic phosphorus from aqueous solutions. The addition of ferric chloride and pyrrole was optimized for complete oxidation and modification of polypyrrole onto red mud. Kinetic studies illustrated that the adsorption progress was accomplished by physical and chemical adsorption. The experimental data of the optimized PRM were described well by Langmuir isotherm, and the equilibrium adsorption capacity was 32.9 and 54.7 mg/g for inorganic and organic phosphorus, respectively. The PRM showed commendable adsorption performance despite the pH conditions ranging from 3 to 11. From the effect of ion strength and X-ray photoelectron spectroscopy (XPS) tests, we found that ligand exchange is the main mechanism of orthophosphate adsorption onto PRM, while electrostatic attraction played an important role in organic phosphorus adsorption. The adsorption performance from column studies showed that the velocity of flow influenced the breakthrough time of the column but the initial concentration had minor impacts. This study would extend the potential application of polypyrrole modified red mud, acting as an efficient adsorbent for inorganic and organic phosphorus adsorption in water treatment.