Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Tuning the composition of new brushite/vivianite mixed systems for superior heavy metal removal efficiency from contaminated waters M.K. Ahmed a, *, S.F. Mansour b,c , Rania Ramadan d , M. Afifi e , Mervat S. Mostafa f , S.I. El-dek g , Vuk Uskoković h, * a Department of Physics, Faculty of Science, Suez University, Suez, Egypt b Physics Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia c Physics Department, Faculty of Science, Zagazig University, Egypt d Materials Science Lab (1), Physics Department, Faculty of Science, Cairo University, Giza, Egypt e Ultrasonic Laboratory, National Institute of Standards, Giza, Egypt f Science and Technology Center of Excellence (STCE), Ministry of Military Production, Cairo, Egypt g Materials Science and Nanotechnology Department, Faculty of Postgraduate Studies for Advanced Science, Beni-Suef University, Egypt h Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA, USA ARTICLE INFO Keywords: Adsorption Coats-Redfern Horowitz–Metzger Mechanical properties Structural refinement Pb(II) Cr(VI) Thermal stability ABSTRACT Calcium phosphates (CPs) are excellent sorbents, with hydroxyapatite being the most commonly used for heavy metal removal from ecological samples. The use of more acidic brushite as a CP sorbent can be justified by its greater pH compatibility with particular types of soil, such as soil in the areas of high rainfall, but also iron- containing soil prone to oxidative weathering and soil nitrified with ammonium fertilizers. Here, brushite na- noparticles were supplemented with vivianite as another metal phosphate phase and the resulting material was studied at different concentrations of the respective phases (x = 0.0, 0.2, 0.4, 0.8 and 1.0 in Fe x Ca 1-x HPO 4 ·2H 2 O). Structural refinement showed that the weight ratio between the two phases intensely impacted their crystallographic ordering. The modeling of thermal analysis data with the use of Coats-Redfern and Horowitz–Metzger formalisms showed a multifold reduction in the activation energy and in the changes of enthalpy and entropy for both dehydration and decomposition transitions with the introduction of vivanite to brushite. Increasing the vivianite content enhanced the efficacy of the removal of heavy metals from aqueous solutions, but only up to a certain limit. The maximal efficacy, along with hardness and microporosity, was obtained for the x=0.8 composition. For this composition, over 98 % of Pb(II) and 85 % of Cr(VI) were removed from the solution at the standard heavy metal concentrations of 2 ppm. The systematic analysis at different weight ratios between the two constitutive phases allowed for the delineation of a composition with ideal properties for environmental decontamination applications. 1. Introduction Rapid industrialization and progress in new technologies come at the cost of environmental pollution with heavy metals. Because of their dissipative nature and the ability to penetrate even the least permeable biological barriers, these heavy ions are considered a severe threat to human life and the timely treatment of wastewaters and contaminated soils for the removal of these metals is a crucial factor for enabling sustainable industrial development [1]. Lead (Pb) is a highly toxic metal and its release to the environment is tied to a number of technological processes, including armor pro- duction, storage battery manufacturing, metal mining and smelting, and others. Moreover, because of its non-biodegradable nature, its re- sidence time in the environment is extremely long, even for geological timescales [1,2]. Therefore, the efficient environmental remediation of Pb(II) is a serious challenge and a precondition for the preservation of safe water and soil of the ecosystem. A plethora of methodologies have been used before for the heavy metal removal from aqueous solutions, such as electrochemical treatments, chemical precipitation, ion-ex- change polymeric resins, and membrane technology [3]. However, most of these technologies are costly and time-consuming. The devel- opment of an efficient, cheap, fast and eco-friendly sorbent material is one of the most sought goals on the road to sustainable development that does not relinquish the promises of high technologies [4]. https://doi.org/10.1016/j.jwpe.2019.101090 Received 13 August 2019; Received in revised form 17 November 2019; Accepted 18 November 2019 ⁎ Corresponding authors. E-mail addresses: mkaa@zu.edu.eg (M.K. Ahmed), vuk21@yahoo.com (V. Uskoković). Journal of Water Process Engineering xxx (xxxx) xxxx 2214-7144/ © 2019 Elsevier Ltd. All rights reserved. Please cite this article as: M.K. Ahmed, et al., Journal of Water Process Engineering, https://doi.org/10.1016/j.jwpe.2019.101090