Enhanced phosphate removal by thermally pretreated waste oyster shells
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ORIGINAL ARTICLE
Enhanced phosphate removal by thermally pretreated waste oyster shells Thanh‑Tham Tran1 · Ngoc‑Ngan Thi Tran1 · Shigeru Sugiyama2 · Jhy‑Chern Liu1 Received: 8 May 2020 / Accepted: 8 September 2020 © Springer Japan KK, part of Springer Nature 2020
Abstract 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 (pHIEP) of oyster shells to more alkaline range, while surface area decreased from 3.47 to 0.52 m2/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 (Q0) and the adsorption constant (b) increased when using oyster shells preheated at 400 °C. The values of Q0 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 ( Ca5(PO4)3(OH)) was formed on surfaces of oyster shells. Keywords Adsorption · Oyster shell · Phosphate · Precipitation · Wastewater
Introduction Phosphorus is an essential element for life. It is also a crucial material in various industries, including detergents, chemical fertilizers, semiconductors, and emulsifiers manufacturing. Therefore, large amount of phosphorus was discharged to the environment in recent years [1]. The excessive amount of phosphorus causes eutrophication that may threaten the water environment. Thus, control of phosphorus in wastewater is of primary importance.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10163-020-01112-4) contains supplementary material, which is available to authorized users. * Jhy‑Chern Liu [email protected] 1
Department of Chemical Engineering, National Taiwan University of Science and Technology, No. 43 Keelung Road, Section 4, Taipei 106, Taiwan
Department of Applied Chemistry, Graduate School of Technology, Industrial and Social Science, Tokushima University, 2‑1 Minamijyousanjima‑cho, Tokushima 770‑8506, Japan
2
Adsorption process is a common method ideal for phosphate removal in dilute systems. It has some advantages, such as easy for operation, cost-effective, and environmentally friendly [2]. Some low-cost adsorbents originated from agricultural wastes and industrial by-products for phosphorous removal have received enormous interests in recent years [3, 4]. Calcite ( CaCO3), dolomite ((CaMg(CO3)2) and calcite-based adsorbents have exhibited potential for phosphate removal, including waste scallop shell [5], eggshell [6], mussel shell [7] and dolomite (CaMg(CO3)2)
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