The Study On Adsorption Of Phosphate By Layered Ternary Hydroxides

A series of MgAlFe and ZnAlFe layered double hydroxides were synthesized by acoprecipitation method and calcined at different temperature to prepare calcined layered doublehydroxides. The samples were characterized by XRD and FT-IR. The adsorption capacity ofphosphate from simulated wastewater which was prepared by dissolving appropriate amount ofKH₂PO₄on ternary layered double hydroxides were studied. The effect of Al/Fe molar ratio,calcining temperature, contact time, initial pH value, adsorbent dosage, temperature andcompeting ions on phosphate adsorption were investigated. The recycle capability of thematerials were also assessed. The adsorptive dynamics and thermodynamic and mechanism ofphosphate uptake were discussed.MgAlFe and ZnAlFe hydrotalcites have single phase, fine crystallinity, obvious layerstructure. The layer structure would be destroyed with excessive iron.Both CMAF-0.1-300and ZAF-0.8showed excellent performance in adsorption phosphate.The optimum pH were4-11and4-6, the optimum dose were1.5g·L-1and0.6g·L-1respectivelyfor CMAF-0.1-300and ZAF-0.8. Inorganic anions, especially those with more negative charges,had side effects on the adsorption of phosphate. The adsorption action of CMAF-0.1-300andZAF-0.8all followed pseudo second-order model and the Langmuir model. The adsorption ofphosphate on CMAF-0.1-300was spontaneous and endothermic nature. However adsorption ofphosphate on ZAF-0.8was spontaneous and exothermic nature and the optimum activetemperature was30℃. The maximum adsorption capacity of CMAF-0.1-300and ZAF-0.8were27.03mg·g-1and46.95mg·g-1respectively.The regeneration of CMAF-0.1-300and ZAF-0.8may decrease phosphate uptake.Thestructural rebuilding of CMAF-0.1-300played an important role in phosphate adsorption.However, phosphate removal by ZAF-0.8was achieved not only by surface adsorption andion-exchange, but also the formation of layered hopeite mineral Zn3（PO4）2·4H2O on the surfaceof material.