Heavy metals pollution was known to cannot undergo biodegradation, resulting to adverse effects on the environment and biological systems (Imron et al., 2019; Purwanti et al., 2020). Lead was one of the heavy metals, which was the second most toxic metal and often found in the environment, then led to no safe level of lead in drinking water (Adeyemi et al., 2021; Kim et al., 2017; Du et al., 2017). It was acutely toxic to human body when consumed in high concentrations inside cells (Nwaehiri et al., 2020). Under environ-mental lead exposure, the elevated lead blood levels could make the Brain system for the permanent and irreversible damage for human, especially the young children (Cecil et al., 2008). At present, the existing removal technologies for lead-contaminated wastewate mainly include chemical precipitation method (Charerntanyarak L., 1999), ion exchange method (Dabrowski et al., 2004), membrane filtration method (Juang et al., 2000), flotation method (Doyle et al., 2003), adsorption method (Crini G., 2005), biosorption method (Rangabhashiyam et al., 2019) and electrochemical method (Pedersen A. J., 2003). Among them, the adsorption method due to its simple operation process, environmental friendliness and high removal efficiency, was an important method to remove lead ions (Pb2+) from wastewate.
Hence, much more attention had been paid to the adsorbent selection. Such as activated carbon (AC) (Kongsuwan et al., 2009), zeolite (Chong et al., 2013), chitosan (Paulino et al., 2007), ion exchange resins (Dong et al., 2010), industrial solid waste (Yong C.B., 2018), nanomaterials (Li et al., 2020), hydroxyapatite (HAP) (Wang et al., 2017; Aklil et al., 2004; Lei et al., 2015; Wen et al., 2013; Lin et al., 2009; Sandrine et al., 2007; Fernane et al., 2013), were widely used to the adsorption materials. Among them, the HAP with high adsorption efficiency and environmental friendliness had greatly promote practical applications. Wang et al. (Wang et al., 2017) studied the magnetic hydroxyapatite-mixed oxidation of multi-walled carbon nanotubes (mHAP-oMWCNTs) to remove Pb2+ in water, and the results showed that mHAP-oMWCNTs showed better performance than mHAP, mMWCNT and HAP-oMWCNTs. Aklil et al. (Aklil et al., 2004) used calcined hydroxyapatite to adsorb Pb2+, Zn2+ and Cu2+, and found that at pH 5, the adsorption capacity of HAP on Pb2+, Zn2+ and Cu2+ were 85.6, 29.8 and 20.6 mg/L, respectively. Lei et al. (Lei et al., 2015) prepared a hydroxyapatite/chitosan (HAP/CS) porous material with a pore size of 100 ~ 300mm to adsorb Pb2+, and its maximum adsorption capacity was 264.42 mg/g. Meanwhile, adding extra elements could improve the performance of hydroxyapatite. Tang et al. (Wen et al., 2013) prepared Si-CHAP by hydrothermally doping silicon carbon into hydroxyapatite. The results showed that Si-CHAP with a large specific surface area of 323.25 m2/g, thereby enhancing the adsorption capacity.
In this work, a strontium-doped hydroxyapatite (Sr-HAP) was synthesized by the sol-gel method. The Pb2+ adsorption experiment was carried out using the prepared material. Discuss the adsorption behavior and influence of Sr-HAP on Pb2+ under different adsorption conditions. The adsorption kinetic equation and thermodynamic parameters were calculated, and the recycling rate of Sr-HAP was explored. Meanwhile, the Sr-HAP was investigeted by the various analytical techniques, such as x-ray diffractometer, fourier transform infrared, scanning electron microscope, brunauer-emmett-teller, zeta potential analyzer. Fiannly, the adsorption mechanism of Sr-HAP on Pb2+ was explained.