Abstract
Secondary treatment of heavy metal bearing solutions requires highly expensive procedures including the application of ionic exchange resins or activated carbon packed in fixed bed reactors. The use of nanoparticles with magnetic properties as adsorbents can improve metal removal performances allowing for the achievement of high specific surface area. In addition, the simplification of the final solid-liquid separation by magnetic field can avoid the application of packed bed columns. In this study a simple synthetic pathway was optimized to produce copper nanoferrites (CuFe2O4), stable in water, magnetically active and with high specific area, to be further used as sorbent material for heavy metal removal in water solution. The hydrothermal route included surfactant-assisted coprecipitation (performed at different pH), hydrothermal treatment (1h at 120°C), washing with water and hexane, drying, and sintering (performed at 100 and 200°C for 1h). Structure and sizes of CuFe2O4 crystallites were studied as function of coprecipitation pH (8, 10, and 12.5) and sintering temperature (100-200°C). CuFe2O4 powders were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), Brunauer-Emmett- Teller (BET) analysis of porosimetric data. Releasing tests of Fe and Cu at different pH were performed to define the pH range of stability in water. Potentiometric titrations were performed to determine the net charge depending on bulk solution pH. Best samples in terms of magnetic characteristics were obtained at pH 12.5 not depending on the sintering temperature. Mean size of nanoparticles obtained in such conditions was estimated by SEM images as 35-45 nm. BET analysis gave specific surface area of 147.8 ± 0.2 m2/g. CFNs have shown chemical stability in water solutions from pH 6 to 10. Zero charge point was estimated as pH 5.5. Then in the stability range of pH, CFNs present negative surface charge being able to coordinate positively charged heavy metal species.
