Sulfate decontamination from groundwater by metal layered double hydroxides functionalized high phosphorus iron ore waste as a new green adsorbent: Experimental and modeling

- The functionalized high phosphorus Iron ore waste for removal of SO42−.
- The first report of the extended geometric method for adsorption on minerals.
- To determine thermodynamic parameters and find mechanism of sulfate adsorption.

The reuse of mine wastes is an efficient method to reduce disadvantages of the mining operation. High phosphorous iron ore (HPI) waste as a common waste of iron mine has been modified by Ni-Al and Ni-Fe hydroxide metals and utilized as a sulfate adsorbent. These adsorbents were characterized by XRD, XRF, FTIR, SEM, BET and TGA analyses. According to characterization studies, by loading Metal Layered Double Hydroxides (Ni-Al and Ni-Fe hydroxide metals) onto HPI Ore Waste appropriate adsorptive spaces and pores were emerged on the surface of Ni-Fe and Ni-Al HPI which were shown by enhancement intensity of OH bending vibrations in FTIR analysis, increase of Loss On Ignition (L.O.I) value in XRF analysis and the thermal stability reduction in TGA. The RSM method based on central composite design (CCD) was used to investigate the optimum condition. The amount of adsorption in optimum condition led to 34 and 29.89 mg/g for Ni-Al and Ni-Fe HPI, respectively. The equilibrium studies have been carried out by the consideration of Langmuir, Freundlich, Temkin, D-R, Redlich-Peterson, Khan, and Koble-Corrigan isotherm models, which displayed that sulfate adsorption onto both adsorbents were performed favorably and chemically. Sulfate adsorption on to Ni-Al and Ni-Fe HPI occurred by the homogenous and heterogeneous process, respectively. Kinetic studies were performed by applying pseudo-first-order, pseudo-second-order and Boyd models which indicated the chemisorption interaction for all three adsorbents by a controlling step of the film diffusion. The adsorption process was modeled by the extended geometric method by an acceptable estimation fitted well with experimental data. Thermodynamic studies indicate that sulfate adsorption process onto Ni-Al and Ni-Fe HPI were exothermic and associative.