Synthesis of layered double hydroxide from biomass combustion ash and coal fly ash for phosphate removal

In this study, we attempted to synthesize layered double hydroxide (LDH) from biomass combustion ash and coal fly ash for phosphorus removal. There is a big problem that a large amount of these ashes are discharged to dispose at landfill as industrial wastes due to the shortage of landfill sites in Japan. On the other hand, water pollution caused by anions, such as eutrophication with phosphoric acid (PO43-) in wastewater, has become a problem. In this study, the biomass combustion ash and coal fly ash were added to HCl to dissolve cations, Ca2+, Mg2+, Fe3+ and Al3+, in the ash to prepare acidic liquid mixture with a molar ratio of (Ca2+ + Mg2+) / (Fe3+ + Al3+) = 5.2, and the mixture stirred to synthesize the product including LDH at 40 degrees C for 6 h with keeping pH 12.5. As the result, Ca-Mg-Fe-Al LDH was successfully synthesized from the solution extracted from biomass combustion ash and coal fly ash using HCl, and the obtained product showed high phosphorus removal ability. From Langmuir and Freundlich adsorption models to estimate the phosphorus adsorption of the product, Langmuir equation could be more realistic than the Freundlich's equation, and the calculated maximum adsorption capacity is 2.33 mmol/g.