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 (PO4
3−) 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 °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.
In Japan, biomass power generation is being promoted for effective biomass utilization. However, a major problem is the large amount of biomass combustion ash discharged and disposed of as industrial waste. Environmental problems caused by arsenic (As) occur throughout the world, including Japan. In this study, we attempted to synthesize an Fe-type layered double hydroxide (Fe-LDH) from biomass combustion ash for As removal. During this experiment, the combustion ash was added to HCl to dissolve divalent cations, Ca and Mg, in the ash, and then filtrated. Iron chloride hexahydrate (FeCl 3 •6H 2 O) was added to the filtrate to prepare an acidic liquid mixture with a molar ratio of (Ca+Mg)/Fe = 2-2.5, which was added to 0.3 M NaCl solution and stirred for 6 h to synthesize LDH at 20, 40, and 60°C maintaining a pH 8.5, 10.5, and 12.5, respectively. In addition, the As removal ability of the product was investigated. As a result, the product, including Fe-LDH, prepared from the biomass combustion ash at pH 12.5 at 40 o C demonstrated a strong ability to remove arsenite (As(III)) and arsenate (As(V)), and the removal percentage of As(III) using the product was higher than that of As(V).
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