Characteristics Of Cemented Uranium Tailing Backfill Based On Alkali-Activated Slag Under The Synergism Of Functional Minerals

Uranium tailings are kind of long-lived,large-volume,and low(or extremely low)level radioactive solid waste.When uranium tailings are stored on the surface or in a surface reservoir,there are usually corresponding environmental and safety problems.These problems may be reduced when the underground dry filling or cemented filling is used.However,these methods still can not fundamentally solve the problems of radioactive diffusion or uranium leaching.Based on the double goals of safe and efficient disposal of uranium tailings and safe and efficient mining of underground mines,this paper establishes a theoretical and technical system of cemented uranium tailings backfill based on alkali-activated slag under the condition of synergism of functional minerals.By means of field investigation,literature search,laboratory test and theoretical analysis,the mechanical properties and leaching resistance of cemented uranium tailings backfill based on alkali-activated slag under the condition of synergism of functional minerals were studied.It provides a reference for the safe and efficient disposal of uranium tailings and other low(or extremely low)radioactive solid wastes and the construction of green uranium mining and metallurgy.The main research contents and conclusions are as follows:(1)According to the requirements of cement solidified disposal of low and medium-level radioactive wastes and paste filling mining technology,the theoretical and technical system of cemented uranium tailings backfill based on alkali-activated slag under the condition of synergism of functional minerals is established.The quality indexs of cemented uranium tailings backfill mainly includes mechanical properties,chemical stability and leaching resistance.The material composition includes uranium tailings aggregate,slag cementing materials,functional minerals modified materials and water.The key process of preparation and filling process is the reconstruction of particle size distribution of uranium tailings,the diverse compound of filling materials and the in-situ monitoring and dynamic adjustment technology of filling quality.(2)The mechanical properties of different slag under different excitation conditions were studied by uniaxial compression test,and the reasonable slag raw materials and excitation scheme were optimized.The gel formation of alkali-activated slag under the condition of functional minerals was explored by means of SEM,XRD,TG-DSC,FTIR and NMR.The results show that granulated blast furnace slag is a good alkali-activated slag cementing material substrate and liquid sodium silicate is an effective way to activate.The gelling products of alkali-activated slag with functional minerals is mainly C-(A)-S-H gel.The addition of functional minerals improves the content of products with high degree of polymerization,but decreases the content of products with low degree of polymerization,resulting in loose structure or cracks,which affects the porosity and macroscopic mechanical properties to a certain extent.(3)The reasonable mass concentration of uranium tailings filling slurry was studied by rheological parameter test.The preparation scheme of cemented uranium tailings backfill based on alkali-activated slag was studied by orthogonal test.The results show that the filling slurry has the characteristics of"shear thinning",and the reasonable mass concentration range is 80?82%.Quicklime is one of the effective composite materials for preparation of cemented uranium tailings backfill based on alkali-activated slag.The modulus of activator has a significant effect on the early strength of the backfill,and the alkali concentration has a significant effect on the later strength.(4)The mechanical properties of cemented uranium tailings backfill based on alkali-activated slag with functional minerals were studied by uniaxial compression test,brazilian splitting test,freeze-thaw cycle test,dynamic compressive test and static soaking test.The results show that the mechanical properties of cemented uranium tailings backfill based on alkali-activated slag with functional minerals are better than that of cemented uranium tailings backfill based on ordinary silicate.At the age of 28 days,the effect of adding zeolite,sepiolite,silica fume and vermiculit on the uniaxial compressive strength of backfill is weakening effect,while concav-convex soil is intensive effect;the effect of five functional minerals on the tensile strength of the backfill is weakening effect;the strength loss rates of freeze-thaw cyclic and static soaking are less than 25%,and there are no obvious cracks or cracked up;under the condition of dynamic loading,when the content of five functional minerals is in the range of 4?16%,the DIF_Aof the backfill is 1.27?2.44.(5)The leaching resistance of cemented uranium tailings backfill based on alkali-activated slag with functional minerals were tested by non-equilibrium leaching test.The results show that the cemented uranium tailings backfill based on alkali-activated slag with functional minerals has a good fixation effect on the uranium in the uranium tailings,the concentration of uranium in the leaching solution,the leaching rate R_n,and the cumulative fraction leached P_tare all lower than the corresponding national standards.Functional minerals generally have a significant strengthening effect on the leaching resistance of cemented uranium tailings backfill based on alkali-activated slag.The p H of the leaching solution is 10.46?11.32,and the leaching test are always carried out in an alkaline environment;The leaching resistance is the best when functional minerals are present in a reasonable amount,and the leaching resistance strengthening effect of the concave-convex soil at 4%is the most prominent.(6)The pore structure of cemented uranium tailings backfill based on alkali-activated slag with functional minerals was studied by LF-NMR and SEM.The effect of uranium tailings aggregate on the cemented uranium tailings backfill based on alkali-activated slag with functional minerals was verified by FTIR,TG-DSC and NMR.The results show that the porosity of backfill includes interface pore and internal fracture pore of cementing material,which is higher than that of ordinary portland cement uranium tailings backfill.Appropriate amount of functional minerals can reduce the porosity of backfill,and the increase of porosity has adverse effects on the mechanical properties and leaching resistance of backfill.Uranium tailings aggregate has no obvious effect on the gelation reaction of alkali-activated slag with functional minerals.The mechanism of cemented uranium tailings backfill based on alkali-activated slag with functional minerals to fix uranium is the synergistic effect of multiple effects such as split package,adsorption,ion-exchange and precipitation.