CLAUDIA MARIA SIMONESCU, ALINA MELINESCU, MARIA CIUCA, BIANCA ZARNESCU REMOVAL OF COPPER(II) IONS FROM AQUEOUS SOLUTIONS BY HYDROXYAPATITE-BASED MATERIALS PREPARED FROM EGGSHELLS The experimental study aimed to establish the potential applications of the nano- and micrometric powders of hydroxyapatite in the removal processes of Cu(II) ions from synthetic aqueous solutions. For this purpose, hydroxyapatite (HAP) was used in the form of: 1) nanometric powder (labeled nano-HAP), and 2) calcium alginate hydroxyapatite composite microparticles (nicro-HAP-CaAlg). Eggshells have been used as a raw material to obtain HAP. The contact time, pH and Cu(II) concentration in the initial solution have been the main process variables with influence on the Cu(II) ions removal by HAP samples. For both HAP based materials, an optimal pH value of 5 has been established. The nano-HAP powder has a higher Cu(II) adsorption capacity than micro-HAP-CaAlg based on the specific surface area values of nano- and micrometric powders. The adsorption isotherm experiments showed that this process can be described using Langmuir model according to which the adsorption takes place as a monolayer process on an homogeneous surface. The kinetic study revealed that the sorption process of Cu(II) from synthetic aqueous solutions can be described using the pseudo-second order kinetics model according to which the rate-determining step is chemisorption. The values of the retention capacity recommends both powders tested (nano-HAP and micro-HAP-CaAlg) to be used in the Cu(II) loaded water treatment process.