Corrigendum to “Removal of Cd²⁺, Ni²⁺ and PO₄³⁻ from aqueous solution by hydroxyapatite- bentonite clay-nanocellulose composite” [Int. J. Biol. Macromol. 118 (2018) 903–912, (S014181301734953X), (10.1016/j.ijbiomac.2018.06.095)]

The authors regret an error in the data processing of the individual XRD spectra presented in Fig. 5 of the original publication “Removal of Cd2+, Ni2+, and PO43− from aqueous solution by hydroxyapatite-bentonite clay-nanocellulose composite,” published in the International Journal of Biological Macromolecules, 118 (2018): 903–912. We emphasize that the individual spectra were error-free and that the issue arose solely during the data processing phase. This error does not affect the conclusions drawn in the original article. To address this issue, the synthesis of the hydroxyapatite-bentonite clay-nanocellulose (CHA-BENT-NCC) composite was repeated under conditions identical to those described in the original publication, and analysis of newly synthesized CHA-BENT-NCC composite material was conducted. The revised XRD pattern is presented below as Revised Fig. 5, offering a more accurate representation of the material's crystalline structure. Since the identical starting materials used in the original synthesis were unavailable, similar materials were used instead. The bentonite clay used in the original synthesis (Foodin Oy product) was sourced from the Fort Benton Mountains, the United States, whereas in the new synthesis, Finnish bentonite clay from Kaurialan Sauna was utilized. Additionally, while both syntheses employed AaltoCell nanocrystalline cellulose (NCC), the original NCC was laboratory-produced, whereas the synthesis repeated for the new XRD measurement used industrially produced NCC.[Figure presented] The XRD pattern of the composite material revealed several significant diffraction peaks, enabling the identification of its key components. The analysis showed that the characteristic peaks of calcium hydroxyapatite (CHA) were not sharp, indicating low crystallinity. This is likely due to the low-temperature synthesis, which restricts crystallization and prevents the formation of a fully developed crystal structure [1,2]. Furthermore, the characteristic peaks of CHA were observed only at low intensities and are likely overshadowed by the stronger crystalline peaks of the clay structure, thereby obscuring the presence of CHA. However, typical peaks associated with CHA can still be observed at low intensities at 2θ = 26°–27° and 2θ = 30°–34° [1,2]. The bentonite clay (BENT) exhibits characteristic peaks at 2θ ~ 6°, 20°, 21°, 22°, 26°, 28°, 35°, 42°, and 62°, indicating the presence of typical bentonite-associated minerals [3,4]. The characteristic peak of NCC at approximately 2θ ≈ 23° is likely overlapped by the diffraction peaks of bentonite minerals [5,6], which is why this peak cannot be distinctly observed. However, the diffraction peak at approximately 2θ ~ 35° is characteristic of NCC [5]. Additionally, nanocrystalline cellulose (NCC) typically produces identifiable peaks also in the XRD-pattern at 2θ ≈ 14°–17°, indicating amorphous regions in the cellulose structure [5,6]. Nevertheless, distinct peaks are not observed in this region, but the overall shape of the diffraction pattern in this range is highly characteristic of NCC, which may indicate its partially disordered structure and the presence of amorphous domains [5,6].