Nano-oxides immobilize Cd, Pb, and Zn in mine spoils and contaminated soils facilitating plant growth

Nanoparticles with high reactivity can be applied as amendments to remediate soil metal contaminations by immobilizing toxic elements. Nano-oxides of Fe have been studied but Al and Ti nano-oxides have not been tested for their remediation capacity of toxic metals. The potential of synthesized iron (Fe-O), aluminum (Al-O), and titanium (Ti-O) nano-oxides for stabilizing Cd, Pb, and Zn in mine spoil (Chat) and contaminated soil was compared using adsorption studies and a greenhouse experiment. Chat and soil were amended with nano oxides at two rates (25 and 50 g kg-1) and a pot experiment was conducted with sorghum (Sorghum bicolor L. Moench). Leachates were collected twice per week from plant emergence to harvest at maturity and metals were compared against an unamended control. Chat was contaminated with Cd, Pb, and Zn at 84, 1583, and 6154 mg kg-1, and soil at 15, 1260, and 3082 mg kg-1, respectively. Adsorption conformed to the Langmuir linear isotherm and adsorption maxima of metals were in the order of Al-O > Ti-O ≥ Fe-O. Nano-oxides reduced Cd concentration by 28% (Fe-O) to 87% (Ti-O) and Zn concentration by 14% (Fe-O) to 85% (Al-O) in plant tissues compared with unamended Chat. Nano-oxides significantly reduced Cd, Pb, and Zn in leachates and available Cd and Zn in Chat/ soil relative to the respective unamended controls. Nano-oxides can be used to remediate heavy metal contaminated Chat and soil and facilitate plant growth under proper nutrient supplements. Nano-oxides of Al-O and Ti-O remediated metals more effectively than Fe-O

Influence of initial concentrations and pH conditions on uranium adsorption in clays

<p>Batch adsorption experiments were performed to investigate influences of experimental conditions such as initial uranium concentrations (0, 1 x 10<sup>-3</sup>, 1 x 10<sup>-2</sup>, 0.1, 0.5, 1 mg/L) and pHs of solution (4, 7 and 9.5) on uranium adsorption in three types of clay (kaolinite, montmorillonite, and bentonite). For all experiments, the adsorption of uranium could be described by the linear isotherm model at solution concentrations less than 1 mg/L, showing high values of correlation coefficient (R2 > 0.98). The adsorption efficiencies of montmorillonite and kaolinite for all pHs are more than 91% and 87%, respectively. The effect of pH on the adsorption of uranium was not found in kaolinite and montmorillonite for all initial concentrations. However, the adsorption efficiency of bentonite was lower than other clay types (< 75%). Solutions with low initial concentrations (< 1 x 10<sup>-2</sup> mg/L) achieved high efficiencies for adsorption of uranium (> 99%) at all pHs, while low efficiencies were observed in solutions with high initial concentrations (> 0.1 mg/L) at pH 4 (47%), pH 7 (59%) and pH 9.5 (43%). It is concluded that montmorillonite and kaolinite can be used as an effective adsorbent for removing uranium from aqueous solutions.</p>