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  • Enhanced phosphate removal ...
    Tran, Thanh-Tham; Tran, Ngoc-Ngan Thi; Sugiyama, Shigeru; Liu, Jhy-Chern

    Journal of material cycles and waste management, 2021/1, Letnik: 23, Številka: 1
    Journal Article

    Waste oyster shells were used to remove phosphate and the effects of thermal pretreatment were studied. Thermal pretreatment under different conditions (400 °C for 0.5 h, 400 °C for 2 h, and 700 °C for 2 h) shifted the isoelectric point (pH IEP ) of oyster shells to more alkaline range, while surface area decreased from 3.47 to 0.52 m 2 /g when pretreated at 700 °C for 2 h. Phosphate adsorption was enhanced when using pretreated oyster shells. Adsorption fitted well with Langmuir isotherm model. Both the maximum monolayer coverage ( Q 0 ) and the adsorption constant ( b ) increased when using oyster shells preheated at 400 °C. The values of Q 0 and b increased significantly to 5.332 mg/g and 0.728 L/mg, respectively, at pH 10.59 when using oyster shells preheated at 700 °C for 2 h, which could be attributed to the formation of calcium oxide (CaO) as evidenced by analysis of X-ray photoelectron spectroscopy (XPS). Both adsorption and precipitation processes were involved in the reactions as supported by analysis of loaded oyster shells by XPS, and hydroxyapatite (Ca 5 (PO 4 ) 3 (OH)) was formed on surfaces of oyster shells.