Vol.:(0123456789) 1 3 J Polym Environ DOI 10.1007/s10924-017-1101-7 ORIGINAL PAPER In Situ Synthesized Hydroxyapatite—Cellulose Nanofbrils as Biosorbents for Heavy Metal Ions Removal Vijaykiran N. Narwade 1,2  · Rajendra S. Khairnar 1  · Vanja Kokol 2   © Springer Science+Business Media, LLC 2017 up to 1000 °C, however, the CNF-HAp hybrid represent a high-value alternative to relatively costly TCNF. Keywords Cellulose nanofbrils · Hydroxyapatite · In situ synthesis · Hybrid adsorbents · Cobalt adsorption Introduction The presence of heavy metals in the surface and ground water arise from waste streams of mining operations, metal- plating facilities, power generation facilities, electronic device manufacturing units, and tanneries [1–6] and as such poses a major inorganic contamination problem. It is well known that heavy metal ions such as Pb 2+ , Cd 2+ , Hg 2+ , Ni 2+ , and Cu 2+ can cause ruthless health nuisance in animals and human, particularly because of their binding to proteins, nucleic acids, and metabolites, and as such causes either the alteration or loss of biological function as e.g. barricade heme biosynthesis, inhibit several enzymes, or accumulate in the apatite structure of the bone [7–12]. Although cobalt is an essential component of vitamin B 12 and also a promoter of blood cell production [13, 14], it may cause mutations in living cells by its ionizing radia- tion being associated with an increased risk for development of cancer [15]. While cobalt may occur at oxidation levels from −3 to +5, in nature it occurs usually only as a divalent cation Co(II) [16]. In erosive environments it easily under- goes oxidation from Co 2+ to Co 3+ and creates the complex anion Co(OH) 3 −3 . According to international standards, the allowed restriction of cobalt in the irrigation water and live- stock watering is 0.05 mg L −1 [16]. So its removal is a vital concern. Adsorption process is well known method for removal of heavy metal ions, being widely used also in removal of Abstract The synthesis of hydroxyapatite (HAp) in the presence of cellulose nanofbrils (CNF) or TEMPO-oxidized CNF (TCNF) was performed in situ by wet chemical precipi- tation process, using chemical precursors, to hybrid a low- cost biosorbents for removal of Co 2+ as a model heavy metal ion. The removal is investigated by batch adsorption method depending on the pH value, the dosage of adsorbent, initial Co 2+ concentration and the contact time of adsorption. The removal of Co 2+ reached the maximum (87%) at pH 6 by using a dosage of 0.5 g L −1 . The TCNFs is shown to increase the nucleation and growth of the HAp synthesized, provid- ing higher surface area (138 m 2 g −1 ) with lower pore diame- ter (11.89 nm), compared to the CNFs based hybrid (135 m 2 g −1 , 14.42 nm) or pure HAp (118 m 2 g −1 , 13.32 nm), how- ever, both resulting to a higher adsorption capacity (25 mg g −1 ) of Co 2+ compared to HAp or TCNF (20–22 mg g −1 ). The adsorption is follows primarily by pseudo-frst and Elovic order kinetic models which is due to the physisorp- tion of Co 2+ and surface ionic interactions with available negative phosphate (from HAp) and/or carboxylic (from TCNF) groups, ftting well with the Freundlich adsorption isotherm, and secondly due to the ion-exchange mechanism of Co 2+ with Ca 2+ from HAp. Both hybrid adsorbents show good adsorption (≥40%) capacity even after third reusing cycle, and high temperature stability (weight loss of 14%) * Rajendra S. Khairnar rk2kin@yahoo.com * Vanja Kokol vanja.kokol@um.si 1 School of Physical Sciences, Swami Ramanand Teerth Marathwada University, Nanded, MS 431606, India 2 Faculty of Mechanical Engineering, University of Maribor, Smetanova ul. 17, 2000 Maribor, Slovenia