Key Laboratory of Eco-chemical Engineering, Taishan Scholar Advantage and Characteristic Discipline Team of Eco-chemical Process and Technology, Qingdao University of Science and Technology, Qingdao 266042, PR China; College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China.
Key Laboratory of Eco-chemical Engineering, Taishan Scholar Advantage and Characteristic Discipline Team of Eco-chemical Process and Technology, Qingdao University of Science and Technology, Qingdao 266042, PR China; College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China.
Sci Total Environ. 2023 Jan 20;857(Pt 3):159596. doi: 10.1016/j.scitotenv.2022.159596. Epub 2022 Oct 21.
An oxalate-doped hydroxyapatite (O-HAP) was hydrothermally synthesized for aqueous lead (Pb) removal based on the solubility-limiting ability of oxalate and phosphate over pH range 4-9. Free Pb activities in oxalate and/or phosphate systems were controlled by oxalate to form soluble ion pairs Pb-Ox (aq) and Pb-Ox at pH 4-7 while in preference to persist as PbHPO (aq) when pH ≥ 8. Both phosphate and oxalate exhibited excellent efficiency in reducing Pb solubility, causing over 99 % of Pb precipitated from solution following oxalate < oxalate-phosphate < phosphate. The Visual MINTEQ model overestimated dissolved Pb and free Pb in nearly all of the reaction systems due to the ill-defined stability constants and solubility products for Pb ion-pair formation. The addition of phosphate acting as a buffer in Pb-oxalate systems tended to lessen the spontaneous pH shifts within 24 h to equilibrate proton release from Pb precipitation and hydrolysis, indicating lower solubility products and faster kinetics of Pb-phosphate mineral formation. The TEM-EDS, FTIR and XRD identified a block-shaped Pb-oxalate mineral phase as the only precipitate at acidic pH while substituted by phosphate to form rod-shaped Pb(PO)OH and Pb(PO) precipitates as pH increased. The optimum hydrothermal conditions of O-HAP were 433 K, pH 9 and P/Ox doping ratio of 0.5 for 24 h. Batch experiments revealed the endothermic process of O-HAP toward Pb with the maximum adsorption capacity reaching 2333 mg/g at a pH of 7, reaction time of 12 h, initial Pb concentration of 600 mg/L and temperature of 308 K, which were best fitted with the pseudo-second-order kinetic model and Langmuir isotherm. The synergetic mechanisms of O-HAP for Pb removal involved dissolution-precipitation, adsorption and ion exchange. This study provides an insight in developing effective remediation strategies for heavy metal contamination by interacting between low-molecular-weight organic acids and secondary mineral phases.
基于草酸盐和磷酸盐在 pH 值 4-9 范围内的溶解性限制能力，用水热法合成了掺草酸盐的羟基磷灰石（O-HAP）以去除水中的铅（Pb）。通过控制草酸盐的浓度来控制溶液中的游离 Pb 活度，在 pH 值为 4-7 时，形成可溶的 Pb-Ox（aq）和 Pb-Ox 离子对，而在 pH 值≥8 时，则优先形成 PbHPO（aq）。磷酸盐和草酸盐都能有效地降低 Pb 的溶解度，使超过 99%的 Pb 从溶液中沉淀出来，其沉淀效果顺序为草酸盐<草酸盐-磷酸盐<磷酸盐。由于 Pb 离子对形成的稳定常数和溶度积不确定，Visual MINTEQ 模型高估了几乎所有反应体系中的溶解 Pb 和游离 Pb。在 Pb-草酸盐体系中添加磷酸盐作为缓冲剂，可在 24 小时内减轻自发 pH 变化，从而使 Pb 沉淀和水解过程中的质子释放达到平衡，表明 Pb-磷酸盐矿物形成的溶度积更低，动力学更快。TEM-EDS、FTIR 和 XRD 确定了在酸性 pH 值下，唯一的沉淀是块状 Pb-草酸盐矿物相，而随着 pH 值的升高，它被磷酸盐取代，形成棒状的 Pb(PO)OH 和 Pb(PO)沉淀。O-HAP 的最佳水热条件为 433 K、pH 9 和 P/Ox 掺杂比为 0.5，反应时间为 24 小时。批实验结果表明，O-HAP 对 Pb 的吸附是吸热过程，在 pH 值为 7、反应时间为 12 小时、初始 Pb 浓度为 600 mg/L 和温度为 308 K 的条件下，最大吸附容量达到 2333 mg/g，该吸附过程最符合准二级动力学模型和 Langmuir 等温线。O-HAP 去除 Pb 的协同机制包括溶解-沉淀、吸附和离子交换。本研究为通过低分子量有机酸和次生矿物相之间的相互作用开发有效的重金属污染修复策略提供了新的思路。
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