Department of Pharmacy, Kindai University Nara Hospital.
Laboratory of Public Health, Faculty of Pharmacy, Kindai University.
Chem Pharm Bull (Tokyo). 2023;71(8):655-660. doi: 10.1248/cpb.c23-00330.
Eutrophication is caused by the inflow of nutrients, such as phosphorus and nitrogen, into closed waterbodies from wastewater. Calcination of oyster shells greatly increases their capacity for phosphate removal; however, information available on this mechanism and the capacity for phosphate removal under different initial pH values and temperatures is less. Herein, we investigated the utilization of oyster shells for phosphate removal under different pH and temperature conditions. Oyster shell powder (OSP) was calcined in a muffle furnace at temperature ranges of 200-1000 °C. Each OSP sample was added to a phosphate solution and the suspension was shaken under different pH and temperature conditions. The main component of OSP changed from CaCO to CaO after calcination at approx. 800 °C. The amount of phosphate removal by the calcined OSPs at 800 and 1000 °C was higher than that removal by the other OSPs. Further, the amount of calcium elution from the OSPs calcined at 800 and 1000 °C was higher than that elution from the other OSPs. This was because the solubility of CaO was higher than that of CaCO. The amount of phosphate removal by the OSP and calcined OSPs at 200-600 °C was the highest at pH 5-7, and increased with increasing reaction temperature. These findings suggested that the mechanism of phosphate removal may involve adsorption in the OSP and OSPs calcined at 200-600 °C, whereas it is associated with coagulation settling and adsorption in the OSPs calcined at 800 and 1000 °C.
富营养化是由营养物质（如磷和氮）从废水流入封闭水体引起的。牡蛎壳的煅烧大大提高了其去除磷酸盐的能力；然而，关于这种机制以及在不同初始 pH 值和温度下的磷酸盐去除能力的信息较少。在此，我们研究了在不同 pH 和温度条件下利用牡蛎壳去除磷酸盐的情况。将牡蛎壳粉末（OSP）在马弗炉中煅烧，温度范围为 200-1000°C。将每个 OSP 样品加入到磷酸盐溶液中，并在不同的 pH 和温度条件下摇动悬浮液。OSP 的主要成分在煅烧至约 800°C 后从 CaCO 变为 CaO。在 800 和 1000°C 下煅烧的 OSP 去除的磷酸盐量高于其他 OSP。此外，在 800 和 1000°C 下煅烧的 OSP 中钙的洗脱量高于其他 OSP。这是因为 CaO 的溶解度高于 CaCO。在 200-600°C 下 OSP 和煅烧 OSP 去除的磷酸盐量在 pH 5-7 时最高，并随反应温度的升高而增加。这些发现表明，磷酸盐去除的机制可能涉及到 OSP 和在 200-600°C 下煅烧的 OSP 的吸附，而在 800 和 1000°C 下煅烧的 OSP 则与凝结沉淀和吸附有关。
