| Due to the rapid development of the atomic energy industry system,the problem of soil and groundwater pollution caused by radioactive pollutants is also becoming more and more serious,which is a great threat to human health and environment.The study shows that a series of reaction processes in geochemistry can affect the migration and transformation of radioactive materials in soil and ground water at the water rock interface.In this paper,the selection of low concentration uranium containing water solution(5mg/L)as adsorption object,using bentonite as the support load material,using low temperature plasma surface modification technology of preparation of PANI/ bentonite materials,comparative study of bentonite and PANI/ bentonite two kinds of adsorption materials in aqueous solution of U(VI)adsorption process.In this paper,static experiments were conducted to study the effects of different factors,such as p H,ionic strength,contact time,solid-liquid ratio,temperature and coexisting substances(HA)on the adsorption process,and explore the reaction mechanism.The main contents and conclusions of this paper are as follows:(1)Adsorption of U(VI)in aqueous solution by BentoniteThe adsorption of bentonite to U(VI)was obviously affected by p H: the best p H for adsorbing U(VI)was 7.In the range of p H 3.0-7.0,the adsorption rate increases with the increase of p H,and the adsorption rate decreases with the increase of p H value at p H > 7.In addition,the effect of ionic strength on the adsorption of U(VI)by bentonite is equally significant.The effect of ionic strength on the bentonite adsorption is different;when p H < 7,[Na+] and U(VI)in the process of the formation of competitive adsorption,ion exchange is the main mechanism of bentonite adsorption of uranium;if p H is greater than 7,the inner surface complexation is the main adsorption mechanism of uranium adsorption on bentonite.The effect of humic acid on adsorption of U(VI)was different.Under the condition of p H < 7,the presence of humic acid greatly promoted the adsorption of uranium on bentonite.When p H > 7,the presence of HA inhibited the adsorption of uranium on bentonite.The kinetics of adsorption of U(VI)on bentonite accorded with the pseudo-second-order kinetics model,and the adsorption equilibrium time was 6h.The adsorption of bentonite to U(VI)is more in line with the Langmuir model.The increase of temperature is beneficial to the adsorption of U(VI)on bentonite.Bentonite has excellent stability,and its adsorption of U(VI)can be recycled.(2)Adsorption of U(VI)in aqueous solution by PANI/bentoniteThe results of the characterization of XRD,XPS,TGA,SEM and BET showed that the PANI/bentonite was successfully synthesized by the surface modification technology of Nonthermal plasma.The adsorption of U(VI)on PANI/bentonite was significantly affected by the initial p H of the solution.The optimum p H for the adsorption of U(VI)is 6.5.At p H=2.0,the adsorption of U(VI)by PANI/bentonite is very poor and the adsorption rate is very low.In the p H range of 4.0-6.5,the adsorption of U(VI)by PANI/bentonite rapidly increases.At p H>6.5,the adsorption rate of U(VI)on PANI/bentonite gradually decreased with the increase of p H value.The effect of ionic strength on the adsorption of U(VI)by PANI/bentonite composites is also significant.High ionic strength can inhibit the adsorption of U(VI)by PANI/bentonite.The adsorption efficiency of U(VI)with PANI/bentonite increased with the increase of solid-liquid ratio.Influence of coexistent ion HA: At p H<6.5,the presence of HA promotes the adsorption of uranium by PANI/bentonite.At p H>6.5,the presence of HA inhibits the adsorption of uranium by PANI/bentonite.The reaction kinetics of adsorption of U(VI)on PANI/bentonite was in accordance with the pseudo-secondorder kinetic equation,and the equilibrium time was 6 h.The adsorption of U(VI)by PANI/bentonite conformed to the Langmuir model,and the adsorption amount increased with the increase of temperature.PANI/bentonite also has excellent stability and can be used for recycling. |
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