Enhanced adsorption of uranium onto humicacid modified goethite from aqueous solution: An soil environmental perspective

Uranium (U) pollution in soil resulted by human activities is a critical environmental issue. Goethite and humic acid (HA), as predominant soil constituents, significantly influence the migration and transformation of uranium in soil, but effects of combining them together on the sequestration and immobilization of U at different mineralization condition are still rare. To simulate the ability of different combinations of HA and goethite to limit the migration of uranium (VI) in the soil environment, the humic acid-modified goethite (OPHG, TSHG) were synthesized by one-pot and two steps synthesis methods in this study. After modified by HA, the specific surface area of materials increased from 29.67 m2/g to 121.53 m2/g and 39.89 m2/g respectively. The effects of dosage, contact time, pH, initial concentration and temperature on the removal of U(VI) by goethite and modified goethite were investigated. The results showed the maximum difference of them reached 41.59% and 15.69 mg/g for reaction 60 min at pH=4.5. The equilibrium adsorption data fit to the pseudo-second-order kinetics and Langmuir models, and the maximum adsorption capacities increased from 64.63 mg/g to 92.04 mg/g. The analyses results indicated that OPHG remove U(VI) mainly through the formation of equivalent to FeOUO2OH between Fe-O and uranyl ions, as well as the complexation of carboxyl and hydroxyl groups on HA molecules with uranium to form the HA-Goethite-U(VI) ternary complexes FeOHAUO2. These results are benefited for understanding the effects of HA and goethite on immobilization uranium in soil and would be used to predict and remediate the polluted soil.