Synthesis and Characterization of Iron Nanoparticles from Acid Mine Drainage Using Sodium Borohydride as Reductant

The large volume of toxic acid mine drainage wastewater generated from the pyritic oxidation of coal and gold mine result in serious environmental pollution because of the problem of waste disposal. The aim of this study is to use iron-rich raw acid mine drainage (RAMD) as a substitute to commercial reagent grade iron salt to synthesize iron nanoparticles. Chemical reduction method was employed to synthesize iron nanoparticles using sodium borohydride as reductant. The synthesized iron nanoparticles from RAMD and reagent grade iron salt solutions were quantified and characterized using analytical techniques such as ion chromatography (IC), Inductively coupled plasma-optical-emission spectroscopy (ICP-OES), X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), High resolution transmission electron microscopy-Selected area electron diffraction (HRTEM-SAED), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET), Fourier Transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and Thermogravimetric analysis (TGA). The ICP-OES result revealed high iron concentration (4784.13 mg/L) and IC sulphate concentration (27, 204. 72 mg/L that iron sulphate salt was present in the RAMD solution. XRD results identified magnetic pure iron mineral phase for both samples and the SEM results revealed spherical crystal particle morphology as long interwoven strand with beads. The HRTEM results revealed a bead-like necklace structure with average particle size of 28.48 ± 4.2 nm and 24.23 ± 2.17 nm for iron nanoparticles synthesized from RAMD (A) and ferric chloride (B) respectively. The XRF elemental composition of the synthesized nanoparticles revealed A (97.4%) and B (99.9%) iron (Fe). BET surface area results for A is 89 ± 3.13 m<sup>2</sup>/g and B is 93 ± 3.16 m<sup>2</sup>/g, FTIR results revealed O-H, CO<sub>2</sub>, Fe and FeO absorption peaks and the AFM results revealed more agglomeration in sample A than in B. The TGA of both synthesized iron nanoparticles were thermally stable. In conclusion, the iron-rich RAMD wastewater was found to be a good substitute for reagent grade iron salt use for making quality iron nanoparticles.