Performance of oxalate-doped hydroxyapatite as well as relative contribution of oxalate and phosphate for aqueous lead removal

Haojie Fu; Xinxin Li; Guoqing Dai; Maojuan Bai; Wei Sheng; Xu Zhang; Juan Liu; Lei Wang

doi:10.1016/j.scitotenv.2022.159596

Performance of oxalate-doped hydroxyapatite as well as relative contribution of oxalate and phosphate for aqueous lead removal

Sci Total Environ. 2023 Jan 20;857(Pt 3):159596. doi: 10.1016/j.scitotenv.2022.159596. Epub 2022 Oct 21.

Authors

Haojie Fu¹, Xinxin Li², Guoqing Dai¹, Maojuan Bai³, Wei Sheng⁴, Xu Zhang⁵, Juan Liu⁶, Lei Wang⁷

Affiliations

¹ 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.
² 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. Electronic address: lixx@qust.edu.cn.
³ College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China.
⁴ China Railway Construction Bridge Engineering Bureau Group Co., Ltd, Zhaoyuan 265400, PR China.
⁵ School of Architecture and Urban Planning, Shandong Jianzhu University, Jinan 250101, PR China.
⁶ 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. Electronic address: Liujuan@qust.edu.cn.
⁷ 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; College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China.

PMID: 36280073
DOI: 10.1016/j.scitotenv.2022.159596

Abstract

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 Pb²⁺ activities in oxalate and/or phosphate systems were controlled by oxalate to form soluble ion pairs Pb-Ox (aq) and Pb-Ox₂^2- at pH 4-7 while in preference to persist as PbHPO₄ (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 Pb²⁺ 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 Pb₅(PO₄)₃OH and Pb₃(PO₄)₂ 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.

Keywords: Aqueous lead removal; Oxalate; Oxalate-doped hydroxyapatite; Phosphate; Synergetic mechanisms.

MeSH terms

Adsorption
Durapatite*
Hydrogen-Ion Concentration
Kinetics
Lead
Organic Chemicals
Oxalates
Water Pollutants, Chemical*

Substances

Durapatite
Lead
Oxalates
Organic Chemicals
Water Pollutants, Chemical