Study On The Formation Mechanism And Plugging Method Of The Preferential Flow Paths For A Novel Rare Earth Pile During Leaching

In order to solve the problem of vegetation restoration in the traditional heap leaching of rare earths,a novel heap leaching technology suitable for vegetation restoration has been creatively proposed.In the novel technology,rare earth ore is horizontally stacked in stages,and the leaching liquid is laterally injected into the rare earth pile from the side end so that space is reserved for vegetation restoration on the top of the pile.This can achieve simultaneous rare earth leaching and vegetation restoration in the heap leaching field,reducing ecological damage to the field.However,a significant issue during the leaching process is the formation of the preferential flow paths in the heap,which negatively affects both the leaching efficiency and stability of the heap.Therefore,studying the formation mechanism and plug method of the preferential flow paths during leaching process is of great significance for the promotion and application of the novel heap leaching technology.Aim at the lateral injection scheme of the novel heap leaching technology,this study employed the method of combining laboratory experiments and numerical simulation.The research aims to explore the formation mechanism of preferential flow paths in the ion-adsorbed rare earth heap under lateral injection,and assess the effect of the formation and distribution of preferential flow paths on leaching efficiency.A method for plugging preferential flow paths in the rare earth heap using rare earth fine particles was proposed and analyzed.The main conclusion are as follows:(1)An indoor model experiment was carried out to reveal the formation of preferential flow paths under lateral injection.The results indicate that,under lateral injection conditions,rare earth fine particles move away from the injection end and migrate towards the lower part of the heap.The migration of fine particles led to the lack of filling between the coarse particle skeleton in local positions,thus forming preferential flow paths.Preferential flow paths mainly appear at the position near the injection end of the lower part of the heap,where the hydraulic pressure is higher.The appearance of preferential flow paths causes the permeability of the lower part of the heap to be significantly faster than that of the upper part.(2)The particle migration rules and permeability characteristics of ion-adsorption rare earth heap under lateral injection conditions were studied by indoor model experiments.The effect of particle combinations at different particle sizes on the permeability of the heap was analyzed,and the formation mechanism of preferential flow paths in the ion-adsorption rare earth heap under lateral injection conditions was revealed.The results indicate that,with an increase in the injection pressure of the leaching solution,the movement of rare earth fine particles can be divided into stable,mobilization,deposition,and re-mobilization stages,resulting in changes in permeability coefficients of rare earth,which presents a process of stable,gradually increasing,stable again,and increasing again.The migration and exudation of the fine rare earth particles result in uneven distribution of the permeability in the pile.Specifically,the permeability is higher at both ends and lower in the middle of the rare earth pile.The particle combinations at different particle sizes have an important effect on the permeability of the rare earth pile under lateral injection conditions.For soils with a coarse-fine particle combination,fine particles migrate more easily and difficult to deposition,leading to the formation of preferential flow paths.While for soils with a medium-fine particle combination,the degree of fine particle migration is relatively low,and the permeability coefficient changes more slowly with increasing pressure head.(3)The numerical simulation based on the Dual-Permeability model in COMSOL was used.In this study,the seepage characteristics of leaching solution in rare earth pile with preferential flow paths were studied,and the influence of the formation and distribution of preferential flow paths on the leaching efficiency of heap was analyzed.The results indicate that,the development area,development angle,and proportion of preferential flow paths have a significant impact on the seepage characteristics and the leaching efficiency,while the transformation degree between the matrix domain and preferential flow domain has a minor effect.The existence of preferential flow paths accelerated the seepage of leaching solution to the bottom of the pile and the advance speed of the wetting front in the development area.This causes a slower increase in the saturation rate at the top of the heap,making it difficult to reach saturation.When the preferential flow paths are fully developed inside the heap,the leaching area decreases the most.When the development angle of preferential flow paths is 45°,the water exchange between the preferential flow domain and the matrix domain is the strongest,and the leaching efficiency is reduced the most,by 28.09%.As the proportion of preferential flow paths increases,the time of water exchange is advanced,and the leaching efficiency decreases.With the increase of the transition coefficient between the matrix domain and the preferential flow domain,the degree of water exchange between the preferential flow domain and the matrix domain increases,but the impact on leaching efficiency is relatively small.(4)Aiming at the formation mechanism of preferential flow paths in ionadsorption rare earth heap under lateral injection conditions,a plugging technique of injecting fine particle slurry into the preferential flow paths was proposed.A model experiment was conducted to validate the effectiveness of the plugging technique.The results indicate that,the smaller the particle size of rare earth particles in the plugging slurry,the better the stability of the slurry,and the less likely the particles are to settle.Using 0.15 mm rare earth particles as the plugging material is effective.The effective plugging area is mainly distributed near the ore leaching inlet.As the proportion of fine particles in the plugging slurry increases,the formation time and position of the plugging area will shift forward.After plugging,the seepage flow decreases,among which the slurry with rare earth particle content of 30% and 40% has the smallest seepage flow.