Study of simultaneous adsorption of ammonium and phosphate in waters by La-F4A zeolites prepared from spent FCC catalyst

Abstract

The problem of resource disposal of massive spent fluid catalytic catalyst needs to be solved urgently. Thus an environmentally friendly, highly efficient and economical cost adsorbent used for nitrogen and phosphorus removal was prepared from spent fluid catalytic catalyst. A novel 4A zeolite adsorbent loaded with lanthanum hydroxide (La-F4A) was prepared by acid leaching pretreatment, alkali fusion roasting hydrothermal and co-precipitation method. And use La-F4A in the study of simultaneous adsorption of ammonia-nitrogen and phosphorus in water. Adsorption experiments were carried out under the condition that the primordial concentrations of PO4 and NH4+-N were respectively 1 & 10mg/L. La-F4A has an adaptive adsorption ability on NH4+-N and PO4 in the pH range of 4-9. When the temperature is 298K, the dosage is 1.0 g/L, the contact time is 240 min, and test water pH=7, the maximum adsorption capacities for NH4+-N and PO4 are 7.64 mg/g and 0.93 mg/g respectively. The behaviours accord with the pseudo-second-order adsorption kinetic model. The adsorption of PO4 conforms to the Langmuir isotherm model while NH4+-N conforms to the Freundlich isotherm model. Coexisting anions have almost no effect on the adsorption of PO4, coexisting cations have different inhibitory effects on the adsorption of NH4+-N. After four desorption cycles, the removal efficiency of La-F4A for NH4+-N and PO4 was 77% and 93% of the initial capacity. There are both chemical adsorption and physical adsorption in the process. The ammonium removal mechanism is the ion exchange between NH4+ and Na+ in the framework, and the phosphate removal mechanism is the ligand exchange between PO4 and hydroxyl to form LaPO4. La-F4A is regarded to be an excellent adsorbent for ammonium and phosphate removal.