K. Nalwa, A. Thakur , N. Sharma, “Synthesis of ZnO nanoparticles and its application in adsorption,” Advanced Materials Proceedings, 2, 11, 697-703, 2017.
 A.M. Ahmed, A. E. Ali , A. H. Ghazy, “Adsorption separation of nickel from wastewater by using olive stones,” Advanced Journal of Chemistry-Section A, 2, 1, 79-93, 2019.
 WHO, “Guidelines for drinking-water quality,” fourth edition, 2012.
 Iraqi regulation, “Environmental legislation,” Chapter XI”, 2001.
 A. Baysal, N. Ozbek , S. Akman, “Determination of trace metals in waste water and their removal processes,” Waste Water - Treatment Technologies and Recent Analytical Developments. Ch.7, 2013.
 M. K. Moftakhar, M. R. Yaftian, M. Ghorbanloo, “Adsorption efficiency, thermodynamics and kinetics of Schiff base-modified nanoparticles for removal of heavy metals,” Int. J. Environ. Sci. Technol.13:1707–1722, 2016.
 A. A. Alswata, M. B. Ahmad , N. M. Al-Hada, “Preparation of zeolite/zinc oxide nano composites for toxic metals removal from water,” Results in Physics, 7,723–731, 2017.
 P. Bartczak, M. Norman, M. Wysokowski, J. Zdarta, F. Ciesielczyk, T. Jesionowski, “Removal of nickel (II) and lead (II) ions from aqueous solution using peat as a low-cost adsorbent: A kinetic and equilibrium study,” Arabian Journal of Chemistry, 11, 1209–1222, 2018.
 C.I. Lin, L.H. Wang, “Adsorption of nickel (ii) ion from aqueous solution using rice hull ash,” Journal of chemical engineering of Japan, 29, 2011.
 K. Atkovska, K. Lisichkov, G. Ruseska, A. T. Dimitrov, A. Grozdanov, “Removal of heavy metal ions from wastewater using conventional and nanosorbents: a review,” Journal of Chemical Technology and Metallurgy, 53, 2, 202-219, 2018.
 A. Ashfaq, A. Ali, R. Goel, S. Ram, “Removal of nickel ions from aqueous solutions using fly ash: equilibrium and kinetic studies,” International Journal of Advance Research in Science and engineering, 6, 5, 2017.
 L. F. Muhaisen, “Nickel ions removal from aqueous solutions using sawdust as adsorbent: equilibrium, kinetic and thermodynamic studies,” Journal of Engineering and Sustainable Development, 21, 03, 2017.
 B. Olufemi1, O. Eniodunmo1, “Adsorption of nickel(II) ions from aqueous solution using banana peel and coconut shell,” International Journal of Technology, 9, 3, 434, 2018.
 I. Aloma, M.A. Martin-Lara, I.L. Rodriguez, G. Bla´zquez, M. Calero, “Removal of nickel (II) ions from aqueous solutions by biosorption on sugarcane bagasse,” Journal of the Taiwan Institute of Chemical Engineers, 43, 275–281, 2012.
 A. I. Zouboulis, K. A. Kydros, “Use of red mud for toxic metals removal: the case of nickel,” J. Chem. Tech. BiotechnoL, 58, 95-101, 1993.
 Z. Hejri, M. Hejri, M. Omidvar, S. Morshedi, “Synthesis of TiO2/nZVI nanocomposite for nitrate removal from aqueous solution,” International Journal of Industrial Chemistry, 21,1,2019.
 S. Mahdavi , M. Jalali, A. Afkhami, “Heavy metals removal from aqueous solutions by Al2O3nanoparticles modified with natural and chemical modifiers,” Clean Techn Environ Policy, 17,85–102, 2015.
 S. Mahdavi , M. Jalali, A. Afkhami, “Removal of heavy metals from aqueous solutions using Fe3O4, ZnO, and CuO nanoparticles,” J Nano part Res., 14,846, 2012.
 E. A. Deliyanni, G. Z. Kyzas, K. S. Triantafyllidis, K. A. Matis, “Activated carbons for the removal of heavy metal Ions : A systematic review of recent literature focused on lead and arsenic ions,” Open Chem., 13, 699–708, 2015.
 G. Yuvaraja, C. Prasad, Y. Vijaya, M. V. Subbaiah, “Application of ZnO nanorods as an adsorbent material for the removal of As (III) from aqueous solution: kinetics, isotherms and thermodynamic studies,” International Journal of Industrial Chemistry, 9, 17–25, 2018.
 S. Singh, L. K. Verma, S. S. Sambi, S. K. Sharma,” Adsorption behavior of Ni(II) from water onto zeolite X: kinetics and equilibrium studies,” Proceedings of the World Congress on Engineering and Computer Science , October 22 - 24, San Francisco, USA, 2008.
 S. Erol , M. Ozdemir.,“Kinetics, equilibrium and thermodynamics studies on Cd(II) removal from aqueous solution by magnesite tailing,” Indian Journal of Chemical Technology, 25, 246-254, 2018.
 L. M. Cozmuta, A. M. Cozmuta, A. Peter, C. Nicula, E. B. Nsimba, H. Tutu, “The influence of pH on the adsorption of lead by Na-clinoptilolite: Kinetic and equilibrium studies,” Water SA, 38, 2, 2012.
 A. A. Alswata, M. B. Ahmad, N. M. Al-Hada, H. M. Kamari, M. Z. Hussein, N. A. Ibrahim, “Preparation of zeolite/zinc oxide nanocomposites for toxic metals removal from water,” Results in Physics, 7 723–731, , 2017.
 K. Nalwa, A. Thakur, N. Sharma, “Synthesis of ZnO nanoparticles and its application in adsorption,” Advanced Materials Proceedings, 2, 11, 697-703, 2017.
 M. Malakootian, N. Yousefi, A.Fatehizadeh, S. W. Van Ginkel, M. Ghorbani, S. Rahimi, M. Ahmadian, “Nickel (II) removal from industrial plating effluent by fenton process,” Environmental Engineering and Management Journal ,14,4, 837-842, 2015.
R. Jeyachitra, N. Sriharan, V. Senthilnathan, T. S. Senthil, “Effect of Ni doping on structural, optical and photocatalytic properties of Zn1-X Ni X O nanoparticles prepared by different pH conditions,” Journal of Advances in Chemistry, 12,6,2016.
 D. Sud , G. Mahajan , M. P. Kaur, “Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions – a review,” Bioresource Technology, 99, 6017–6027, 2008.
 M. H. Ali, A. M. Abdel-Satar, “Removal of some heavy metals from aqueous solutions using natural wastes orange peel activated carbon,” IJRDO-Journal of Applied Science, 3,3, 2017.
A. Heidaria, H. Younesi, Z. Mehraban, H. Heikkinen, “Selective adsorption of Pb(II), Cd(II), and Ni(II) ions from aqueous solution using chitosan–MAA nanoparticles,” International Journal of Biological Macromolecules,9,22,2013.
 R. B. Shaikh, B. Saifullah, F. U. Rehman, “Greener method for the removal of toxic metal ions from the wastewater by application of agricultural waste as an adsorbent,” Water, 10, 10, 2018.
 A. Çitak, “Synthesis, characterization, and kinetic studies of multi-functionalized mesoporous silica for adsorption of zinc,” Turkish Journal of Chemistry, 43, 106 – 117, 2019.
 K. M. Nguyen, B. Q. Nguyen, H. T. Nguyen, T.H. Nguyen, “Adsorption of arsenic and heavy metals from solutions by unmodified iron-ore sludge, Applied Sciences, 9, 619, 2019.
 L. A. Ahmed, “Removal of heavy metals from waste water by date palm tree wastes,” Eng. &Tech. Journal, 28, 1, 2010.
 M. M. Brboot, B. A. Abid , N. M. Al-Shuwaiki, “Removal of heavy metals using chemicals precipitation,” Eng. & Tech. Journal, 29, 3, 2011.
 I. Kula, M. Ug˘urlu , H. Karaog˘lu, A. Celik, “Adsorption of Cd(II) ions from aqueous solutions using activated carbon prepared from olive stone by ZnCl2activation,” Bioresource Technology, 99, 492–501, 2008.
 M. I. Khan, S. Akhtar, S. Zafar, A. Shaheen, M. A. Khan, R. Luque , A. Rehman, “Removal of congo red from aqueous solution by anion exchange membrane (ebtac): adsorption kinetics and thermodynamics,” Materials, 8, 4147-4161, 2015.
 P. Saha, S. Chowdhury, “Insight into adsorption thermodynamics,” Thermodynamics- chapter 16,349-367, Licensee Intech Open, 2011.