Simultaneous removal of Cu (II) and Cr (VI) ions from petroleum refinery wastewater using ZnO/Fe3O4 nanocomposite.

The presence and removal of heavy metals such as Cu(II) as well as Cr(VI) in petroleum refinery wastewater calls for concerted efforts due to their mobility, toxicity, bioaccumulation, and non-biodegradability in the environment. In this present work, zinc oxide (ZnO), iron oxide (Fe3O4) nanoparticles and ZnO/Fe3O4 nanocomposites were synthesized via simple sol-gel and chemical reduction methods; characterized using different analytical tools and then applied as nanoadsorbent to sequester Cu(II) and Cr(VI) ions from Petroleum Refinery wastewater via batch adsorption process. Cu(II) and Cr(VI) adsorption processes were examined with respect to contact time (kinetic effect), nanoadsorbent dosage, isotherm equilibrium, and thermodynamic parameters. ZnO/Fe3O4 nanocomposites with higher surface area (39.450 m2/g) have a mixture of rod-like and spherical shapes as compared to ZnO and Fe3O4 nanoparticles with spherical shape only and surface areas of 8.62 m2/g and 7.86 m2/g) according to the high-resolution scanning electron microscopy (HRSEM) and Brunauer-Emmett-Teller (BET) analysis. The X-ray diffractometer (XRD) results revealed the formation of hexagonal wurtzite structure of ZnO and the face-centered cubic structure phase of Fe3O4 nanoparticles, after the formation of the ZnO/Fe3O4 nanocomposites the phases of the nanoparticles were not affected but the diffraction peaks shifted to higher 2θ degree. The average crystallite size of ZnO and Fe3O4 nanoparticles and ZnO/Fe3O4 nanocomposites were 20.12, 26.36 and 14.50 nm respectively. The maximum removal efficiency of Cu (II) (92.99%) and Cr (VI) (77.60%) by ZnO/Fe3O4 nanocomposites was higher than 85.83%; 65.19% for Cu (II) and 80.57%; 62.53 for Cr (VI) using ZnO and Fe3O4 nanoadsorbents individually under the following conditions: contact time (15), dosage (0.08 g) and temperature (30 °C). The experimental data for Cu (II) and Cr (VI) ion removal fitted well to the pseudo-second-order kinetic and Langmuir isotherm models. The thermodynamic study suggested that the removal of the two metal ions from petroleum wastewater was endothermic. The reusability study after the fourth adsorption-desorption cycle indicated the stability of ZnO/Fe3O4 nanocomposites with 85.51% and 69.42% removal efficiency of Cu (II) and Cr (VI). The results showed that ZnO/Fe3O4 nanocomposite achieves higher performance than ZnO and Fe3O4 alone in the removal of Cu (II) and Cr (VI) ions from the petroleum refinery wastewater.

Assessment of selected heavy metal concentrations in soils from a mining area in Minna, Niger state.

The study investigated the contents of selected heavy metals in top soils and sub-soils around the vicinity of artisanal gold mining site in Minna, Niger state, using standard procedures. Digestion was done using HNO3-H2O2-HCl and heavy metal content using atomic absorption spectrometer. The results obtained showed some extent of contamination with mean values of 2.87 ± 0.17mg kg-1, 286.21 ± 0.20mg kg-1, 15,375.46 ± 0.52mg kg-1, 2233.60 ± 0.46mg kg-1, and 131.71 ± 0.15mg kg-1 for Cd, Zn, Fe, Mn, and Pb, respectively. The surrounding environment (50 m away from the gold mining site) also showed significant contamination with mean values of 2.77 ± 0.17mg kg-1, 295.27 ± 0.20mg kg-1, 11,523.64 ± 0.25mg kg-1, 1956.50 ± 0.54mg kg-1, and 74.63 ± 0.15mg kg-1 for Cd, Zn, Fe, Mn, and Pb, respectively. The values obtained were significantly higher when compared with those from the control soil samples. With the exception of Pb and Mn, the values of the other metals investigated were all below the WHO permissible limit. The trend of contamination with respect to contamination factor was in the order: Zn > Fe > Pb > Mn > Cd. The high contents of Pb and Mn in this area therefore show the need for more studies and immediate intervention measures.