Synthesis of Fe-type Layered Double Hydroxide from Biomass Combustion Ash for Removal of Arsenite and Arsenate

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 (FeCl3·6H2O) 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 40C 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).