The development of novel composite materials of modified roasted date pits using ferrocyanides for the recovery of valuable metal ions from seawater reverse osmosis brine

Abstract

In this project, novel composite materials from modified roasted date pits using ferrocyanides were developed and investigated for the recovery of valuable metal ions (Li+ and Sr2+) from seawater reverse osmosis (RO) brine. Three adsorbents were prepared, namely roasted date pits (RDP), potassium copper hexacyanoferrate, and potassium nickel hexacyanoferrate date pits composites (RDP-FC-Cu and RDP-FC Ni). The physicochemical characteristics of the RO desalination brine and the adsorbents were determined. Various analytical techniques were used such as Inductively coupled plasma atomic emission spectroscopy (ICP-AES), Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDX), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) as well as pH, salinity, conductivity, particle size distribution test, Brunauer Emmett Teller (BET) surface area, and pore size distribution. The RO brine was found to be highly saline, have a crystal structure, and contain a variety of metals as well as salts. RDP FC-Cu and RDP-FC-Ni exhibited enhanced chemical and physical characteristics than RDP. The optimum pH, metal-ion initial concentration, and temperature for all adsorbents were pH 6, 100 mg/L, and 45?, respectively. The RDP-FC-Cu and RDP FC-Ni achieved higher adsorption capacities and efficiencies towards lithium ions than RDP at all the studied pH, concentration ranges as well as temperatures. The RDP-FC Cu was found to be more selective towards lithium than strontium with higher adsorption capabilities than RDP-FC-Ni. To compare, RDP-FC-Ni was more selective towards strontium. All the prepared adsorbents showed high selectivity towards lithium and strontium from the reverse osmosis brine. The adsorption thermodynamics such as Gibbs free energy (Go), enthalpy (Ho), and entropy (So) revealed that the adsorption process of lithium and strontium onto RDP, RDP-FC-Cu, and RDP-FC-Ni were endothermic, spontaneous, and favorable. Furthermore, the adsorption mechanism was well-fitted to Langmuir and Freundlich adsorption isotherms.