Development of Novel Porous Phosphorous Adsorbent by Effective Uses of Waste Cement and Flyash

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Mechano-chemically activated wollastnite powder was used as a starting material to obtain consolidated bodies by a carbonation method. Fly ash as aggregate and hydrated cement as a calcium resource were added to wollastnite in order to improve the phosphorus removal property of the consolidated bodies. The wollastnite consolidated bodies obtained these additives showed higher phosphorus removal ratio than that of pure wollastnite. However, the sample obtained at low carbonation temperature generates fine HAP precipitate in a phosphoric acid aqueous solution due to significant increase in pH. On the other hand, when the carbonation temperature is high, the phosphorus removal ratio markedly decreased. This is caused by the decrease in the dissolved calcium ion concentration due to the carbonation of calcium hydroxide in cement. Therefore, the precise control of carbonation conditions is necessary when the hydrated cement as a calcium resource.When gypsum was used as a calcium resource instead of hydrated cement, the phosphorus removal ratio was independent of the carbonation temperature and higher than that of pure wollastnite. The sample containing gypsum did not generate fine HAP precipitation regardless carbonation temperature. Moreover, the sample containing gypsum showed satisfied phosphorus removal ratio at 25% amount of pure wollastnite.The cyclic immersion test in the phosphoric acid aqueous solution showed the significant decrease of the phosphorus removal ratio with increasing immersion cycle. Five times of immersion decreased the phosphorus removal ratio of the sample to 50% of initial value. However, the phosphorus removal ratio deteriorated sample was recovered to 95% of initial value by washing the sample in 0.005mol/l hydrochloric acid to remove HAP precipitated on the surface of the sample.