| Rare Earth Elements,known as the "vitamins of industry",play an irreplaceable role in a large number of high-tech and material science fields.REE is an important strategic resource of the country and one of the important commodities in the game between major powers.Researchers found the deep-sea sediment contains a large number of rare earth elements in the Western Pacific Ocean′s C-C mining area,which will be of great value to exploit.However,facing the high-pressure environment in the deep-sea and the limitations of extreme mining conditions,traditional theories such as mining science and mechanics are difficult to solve the technical problems of deep mining,especially the problem of transportation.At present,Pipeline transportation is the most commonly used transportation technology in the exploitation of deep-sea mineral resources,however,the deep-sea rich rare earth sediments are different from the ground soil with high water content and obvious fluidity,which directly affects the exploitation of rare earth mineral resources and sediments transport in the pipeline.At present,there is still a lack of systematic research on the rheological properties and the flow laws in pipelines about this kind of deep-sea rich rare earth sediments at home and abroad.Therefore,this paper aimed at the research frontiers of pipeline transport in the process of deep-sea mining,in terms of the problem about how to realize fluidization transportation in the process of deep-sea rare earth mining,the rheological-viscoelastic properties of deep-sea rare earth-rich sediments are studied.Based on computational fluid dynamics simulation,the flow characteristics of deep-sea rare earth-rich sediments in pipelines are analyzed,which provides an important basis for its application in deep-sea rare earth mining technology in China.The main research results of this paper are as follows:(1)The deep-sea rare earth-rich sediments are exploited in the Pacific C-C district.Its physical and mechanical are studied by the test of liquid and plastic limit,specific gravity bottle,analysis of laser particle size,scanning electronic microscope(SEM),Xray Diffraction(XRD).The test result shows that the deep-sea rare earth-rich sediments have a small particle size,mainly composed of powder particles and clay particles,and their content accounts for about 83% of the total particle size.It has properties of high liquid limit,high plasticity,and high specific surface area.Its mineral compositions are mainly composed of primary minerals such as quartz,calcite,stone salt,feldspar,mica,and secondary minerals such as greenstone.The microstructure is mainly composed of link structure and honeycomb flake structure.(2)Based on the deep-sea rare-earth-rich sediments collected from the Pacific CC mining area,its rheological properties and rheological behavior were studied by using the RST rheometer produced by Brookfield Company.The rheological properties of samples such as shear stress,yield stress,viscosity were influence by the shear rate,temperature,and moisture were systematically considered.The results show that the typical rheological curve of deep-sea rare earth-rich sediments can be roughly divided into three stages: solid stage,solid-liquid conversion stage,liquid stage.The samples exhibit non-Newtonian fluid characteristics under shear load,and the apparent viscosity decreases with the increase of shear rate and shear time.Compared with normal temperature conditions,the shear stress and apparent viscosity of the sediment are significantly increased in a low-temperature environment,and the apparent viscosity and yield stress decreased with the increase of water content of sediments.It was found that the sample was standing longer,the yield stress was greater.The Herschel-Bulkley model was introduced to establish a comprehensive rheological model that considering the changes of water content and temperature of samples.(3)Based on computational fluid dynamics(CFD)technology,the transport state of deep-sea RE-rich sediments in the pipeline was simulated.The effects of pipeline diameter,inlet velocity,and rheological parameters on the flow state and pressure drop of deep-sea RE-rich sediments in the pipeline were systematically discussed.We systematically discussed the flow state and pressure drop of deep-sea rare earth-rich sediments in the pipeline under different pipe diameters,inlet velocity,and rheological parameters.The results show that when the inlet velocity is constant,the pressure drop of the pipeline decreases gradually with the increase of the diameter of the pipeline,and when the diameter of the pipeline is small,the pressure drop decreases rapidly,and when the diameter is large,the pressure drop decreases slowly.In the process of sample flow,the maximum velocity appears at the center of the pipe,the minimum velocity at the wall,and decreases from the center to the wall.(4)The viscoelasticity of deep-sea REE-rich sediments was studied by using Anton Paar MCR301 rheometer,according to the test methods of frequency scanning and amplitude scanning.The viscoelastic test results show that,at a strain amplitude ofγ(27)0.01,the sample exhibited linear viscoelastic behavior,and the phase angle of the sample is unchanged.When 0.01(27)γ(27)0.1,G’(29)G ",the sample exhibits nonlinear viscoelastic behavior dominated by elasticity.When γ(29)0.1,G’(27)G",the sample exhibits nonlinear viscoelastic behavior dominated by viscosity,in the nonlinear viscoelastic stage,the phase angle increases nonlinearly with the increase of shear strain amplitude.The results of frequency scanning show that the critical strain amplitude of linear viscoelastic and nonlinear viscoelastic phases of the sample is independent of frequency.Besides,in the linear viscoelastic region,the oscillating shear frequency has little effect on the viscoelastic modulus,however,the oscillating shear frequency has a great effect on the composite viscosity.In the double logarithmic scale,the composite viscosity decreases linearly with the increase of the shear oscillation frequency.(5)Based on the deep-sea rare-earth-rich sediments collected from the Pacific CC mining area,The rheological properties,normal adhesion force,thixotropy,and viscoelastic properties of the samples before and after modification were studied by using three different chemical additives,such as dispersant,water-retaining agent and thickener respectively.The results show that the yield stress and ultimate viscosity,normal adhesive force and normal adhesive strength,thixotropy,and viscoelastic modulus of the modified sample are decreased and the fluidity of the sample is greatly enhanced when the dispersant-polycarboxylic ether is added at the proportion of 1.0%compared with the undisturbed soil.While the yield stress and ultimate viscosity,normal adhesive force and normal adhesive strength,thixotropic properties,and viscoelastic modulus of the samples modified by sodium polyacrylate,polyacrylamide,alkylammonium salt and alkylaryl all increased with the increase of reagent addition ratio.The fluidity decreased and the ability to resist external deformation increased,which was not conducive to the flow of sediments in the pipeline. |
