Adsorption Properties On UO₂²⁺ In Aqueous Solution Of Sunflower Seed Shells

Uranium mining is rapidly increasing with the development of nuclear power in recent years. Uranium mining and processing, nuclear facilities decommissioning and nuclear accident can cause radioactive contamination to the environment. Radioactive contamination is so hard to be treated that it has gained much more attentions among people, especially after the Japan’s Fukushima nuclear power plant explosion in 2011. Therefore, it is important to search for the cost-effective treatment methods to protect the environment,people’s health and economic development.In order to study the uranium adsorption behavior, this paper selected agricultural byproducts sunflower shell as adsorbent. Static experiments to study the effects of modification of sunflower shells, time, temperature, p H, initial uranium concentration, sunflower seed shell dosages were studied by batch experiments., the column experiments were also selected to investigate the dynamic adsorption process. Kinetic and thermodynamic equations, adsorption isotherm models were used for the data analysis. The characterizations which include the specific surface area, elemental analysis, scanning electron microscopy, FT-IR were used for study the adsorption mechanism of a modification sunflower seed shells and original sunflower seed shells.Batch experiments showed that: the modification with hydrochloric acid has little impact on the adsorption properties of sunflower seed shells, sodium hydroxide modification would decrease the uranium removal rate to about 21.49%. The optimum p H was 5-6; temperature had little impact on uranium adsorption onto sunflower seed shells which meant that experiments could be carried out at room temperature; sunflower seed shells had rapid uranium adsorption rate during initial time, and removal rate was over 70% at about 30 min, then become slower and finally reached equilibrium. Adsorption capacity decreased and remove rate increased with the increase of usages of sunflower seed shells, decrease of initial concentration, respectively. Selecting initial uranium concentration =50 mg/L, p H=5.0, the amount =1 g/L, the adsorption capacity is about 29.21 mg/g.Dynamic experimental results showed that the solution flow rate, amount of adsorbent that adsorption column height, the initial concentration of uranyl ion had a great influence on the dynamic adsorption. Increasing the flow rate could cause the breackthrough point/penetration volume to become lower, adsorption capacity and removal efficiency of sunflower seed shells decreased, too. Increasing the adsorbent dosage that increasing the adsorption column height cause the breackthrough point/penetration volume to become higher, adsorption capacity of sunflower seed shells decreased, but removal efficiency of sunflower seed shells increased. Increasing the initial concentration of uranium cause the breackthrough point/penetration volume to become lower, adsorption capacity of sunflower seed shells increased, but removal efficiency of sunflower seed shells decreased. When the flow rate was 150 m L/h, adsorbent dosage was 1.0 g, column height was 3 cm, the uranyl ion initial concentration was 50 mg/L, p H = 5.0, the sunflower seed shells on the adsorption of uranyl ion homeostasis was 41.53 mg/g.Data analysis showed that: sunflower seed shells on the adsorption of uranyl ions was in line with the pseudo-second kinetic model and Freundlich isotherm model; enthalpy was greater than zero which meant that the process was an endothermic process; entropy change is greater than zero, which meant the entropy-driven process; free energy is negative, which represented spontaneous reaction.Characterization results showed that: the specific surface area of sunflower seed shells, sunflower seed shells modified hydrochloric acid, sodium hydroxide modified sunflower seed shells were 0.8323 m2/g, 0.9256 m2/g and 0.4417 m2/g, respectively, sunflower seed shell was surface rough and porous, and had continuous and uniform distribution of pore structure. It is good for adsorption due to the honeycomb pores and penetrating holes. Surface morphology of sunflower seed shells changed little, sodium hydroxide modified sunflower seed shell appeared smooth and compact surface and made the surface area reduced; because of the original pore surface adsorbed UO22+ filled the whole surface looks, reacted sunflower seed shells became more smooth and had low porosity; reacted sunflower seed shells and original ones had a certain degree of changes, but the changes were not great; spectroscopy analysis showed that sunflower seed shells had the capacity for adsorbing UO22+. Modification with the functional group for sunflower seed shells did not increase its adsorption capacity; uranium adsorption onto sunflower seed shells contained both chemisorption hand physical adsorption, and the processes were not a simple superpositions.