http://www.revistadechimie.ro REV. CHIM. (Bucharest) ♦ 66 ♦ No. 5 ♦ 2015 732 Nano and Micro-hydroxyapatite Particles for Lead Removal from Wastewater CLAUDIA MARIA SIMONESCU 1 , ALINA TATARUS 1 , CHRISTU TARDEI 2 *, DELIA PATROI 2 , MIOARA DRAGNE 3 , DANIELA C. CULITA 4 , RODICA-ELENA PATESCU 1 , LAURENTIU TEODOR BUSUIOC 1 , IOANA MELINTE 1 1 University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, 1-7 Polizu Str., 011061 Bucharest, Romania 2 National Institute for R&D in Electrical Engineering ICPE-CA, 313 Splaiul Unirii, 030138, Bucharest, Romania 3 SC KEMCRISTAL SRL, 51 Muncii Str., Fundulea, Cãlãraºi, Romania 4 Romanian Academy, Institute of Physical-Chemistry ”Ilie Murgulescu”, 202 Splaiul Independentei, 060023, Bucharest, Romania Two types of (Ca 10 (PO 4 ) 6 (OH) 2 ) hydroxyapatite (HAP) powders with high purity were obtained using two different synthesis methods – a wet chemical synthesis method such as precipitation from aqueous solution and a dry chemical method such as solid-state sintering. Both types of powders were characterized by X-ray diffraction, FT-IR analysis, scanning electron microscopy (SEM), and N 2 sorption analysis. X-ray diffraction showed that both HAP powders contain hydroxyapatite as the only crystalline phase. Data from X-ray diffraction were confirmed by FT-IR spectra. SEM images showed that nanometric size hydroxyapatite (nano-HAP) was obtained by precipitation from aqueous solution and hydroxyapatite with micrometric size (micro-HAP) was obtained using sintering method as a solid phase synthesis method. Nano-HAP powder has a BET surface area almost 5 times higher than that of the microcrystalline HAP powder. Consequently, both powders were comparatively tested in lead removal process from aqueous solutions. The contact time, the concentration of lead ions in the initial solution, pH and temperature were the main parameters studied. The highest Pb(II) sorption was achieved for nano-HAP. The sorption process was relatively fast because the equilibrium was achieved after about 60-180 min of contact depending on the lead concentration in the initial solution, and the specific surface area of the samples. Results showed that the adsorption behaviour of micro-HAP and nano-HAP follows the Langmuir isotherm. The kinetic process of Pb(II) sorption onto micro-HAP and nano-HAP was tested by applying the pseudo-first order, the pseudo-second order, and intraparticle diffusion models. The experimental data were fitted with pseudo-second order equation. The main mechanism for lead ions removal using synthesized micro-HAP and nano-HAP was suggested to be dissolution of HAP followed by hydroxy-pyromorphite (Pb 5 (PO 4 ) 3 OH) precipitation. From this experimental study, it can be concluded that both sorbents can be successfully applied for lead removal from wastewater. Keywords: sintering, calcination, porosity, hydroxiapatite, environmental applications * email: christu.tardei@icpe-ca.ro Environments contaminated with metals have been extensively studied in recent years, due to the negative effects of the heavy metals on living organisms (plants, animals, humans) [1]. Their negative effects are due to their toxicity, persistence, bioaccumulation and bio- magnification through chain food [2]. Therefore, considerable effort has been made to treat and remediate environments contaminated with heavy metals. Chemical precipitation, ionic exchange, flotation, reverse osmosis, sorption, membrane filtration and electrochemical methods are used as traditional methods to remediate wastewater with heavy metals content [3]. From these techniques, sorption has flexibility in design and operating conditions, leading to effluents with very low content of heavy metals [4]. Another advantage of the sorption process is the fact that sorbents can be regenerated by desorption and they can be reused in several sorption cycles [5]. The sorption process is characterized by low cost, as compared with other heavy metals removal traditional methods. This process is considered one of the most important processes of removing heavy metals from various wastewater sources [6]. Numerous materials such as clays [7], unmodified and modified starch [8], activated carbon, bone meal and iron fines [9], metal oxides and hydroxides [10, 11], by products [12], cellulose [13], carbon nanotubes [14], natural and synthetic zeolites [15], composite materials [16], polymers and hydrogels [17, 18], phosphates [19], saline slags [20], fly ash [21], biomass-derived sorbents [22] have been employed as adsorbents for removal of heavy metals from wastewater and aqueous solutions. It has been demonstrated that the following three steps are involved in heavy metals removal by sorption onto solid sorbents (1) the transport of the heavy metal from the bulk solution to the sorbent surface; (2) adsorption on the particle surface; and (3) transport within the sorbent particle [4]. Selection of the most suitable sorbent to treat wastewater with heavy metals content has to be made taking account by the technical applicability and cost- effectiveness. Thus, intense efforts have been aimed at the development of new heavy metals adsorbents with good sorption capacity, selectivity and low cost [23]. Hydroxyapatite is an important biomaterial studied for applications in medicine [24]. Due to its chemical structure, and structural similarity with the mineral component of bones and teeth, HAP is often used for hard tissue repair. HAP may be used in the form of powder or as composite particles coated with various organic compounds [25]. The use of calcium phosphate as adsorbent is due to its large specific area, high thermal and chemical stability, and high ionic exchange capacity.