Adsorption Removal of Phosphate and Fluoride from Aqueous Solution Using Oily Sludge-based Pyrolysis Residue

In order to explore the potential application of oily sludge-based pyrolysis residue in the treatment of wastewater with phosphate and fluoride, batch adsorption experiments were carried out using the pyrolysis residue with porous structure as an adsorption material. The effects of the residue dosage and initial concentration of phosphate and fluoride on adsorption removal efficiency, as well as adsorption kinetics and isotherms were determined experimentally. The adsorption mechanism was discussed using the techniques of SEM-EDS, XRD, FTIR and Zeta potential test. The results showed that both phosphate and fluoride in aqueous solution can be significantly adsorbed and removed by pyrolysis residue. The adsorption isotherms can be simulated well by Langmuir equation, and the qmax of phosphate and fluoride on the pyrolysis residue were 36.72 and 37.27 mg/g, respectively. The kinetics can be fitted well by the pseudo-second order kinetic equation, showing that the adsorption mechanisms of phosphate and fluoride on pyrolysis residue were chemisorption, and the adsorption rate was controlled by the internal diffusion. The adsorption removal of phosphate and fluoride were due to the formation of CaHPO4·2H2O, Ca3(PO4)2 and CaF2 precipitate on the pyrolysis residue surface. The pyrolysis residue has been proved to be a promising candidate for the removal of phosphate and fluoride from aqueous solution.