The Transport Processes Of Red Mud Filtrate In Saturated Porous Media By Seepage

The effects of flow velocity,the concentration of red mud particles and the concentration of OH-on the penetration process of red mud filtrate in saturated porous media by seepage were studied by laboratory test.Then,the transport parameters based on the convection-diffusion equation have been fitted.The main conclusions are as follows:(1)To study the effect of flow velocity on the migration characteristics of red mud filtrate in saturated porous media,soil column seepage tests of three flow velocities were carried out under two kinds of injection pH and six injection concentrations.The results show that under the same conditions,the larger the flow velocity is,the larger the peak of the concentration of outflow fluid is,and the larger the relative concentration is.This shows that the greater the hydrodynamic,the greater the dispersion.(2)To study the effect of OH-on the migration characteristics of red mud filtrate in saturated porous media,soil column seepage tests with no alkali and injection pH =12 were carried out under six kinds of injection concentrations and three flow velocities.The results showed that the peak concentration of the breakthrough curves(BTCs)of red mud filtrate with high alkalinity was significantly higher than that with low alkalinity.This indicates that the presence of OH-has enhanced the repulsion between red mud particles and between red mud particles and the matrix,and promoted the migration of red mud filtrate.Under the condition of high alkalinity,the peak of the breakthrough curves appears earlier,indicating that the presence of OH-accelerates the diffusion of red mud filtrate.(3)To study the effect of the concentration of injection solution on the migration characteristics of red mud filtrate in saturated porous media,six kinds of injection experiments were carried out under two kinds of injection pH and three flow velocities.The results show that the larger the injection concentration is,the more regular the BTCs is,which is affected by the random motion during the migration process.With the increase of the concentration of the injected particles,the peak concentration of the outflow fluid increases,while the relative concentration decreases first and then increases,this reflects the complex evolution trend of the depositional effect.(4)Comparison of red mud filtrate and silica powder suspension:The red mud particles are more easily absorb onto the surface of porous material or embedded in the matrix than silicon powders due to the greater adsorption between red mud particles and porous dielectric matrix during the penetration processes,which is closely related to their material composition,irregular particle shape and strong physical-chemical action,which the peak of the breakthrough curves of red mud filtrate is lower than the peak of silicon powder.(5)Comparison of the breakthrough curves of red mud filtrate and the curves of pH changes:The velocity of suspended particles with a large diameter,like the red mud particles,is often slower than that of water due to the capture effect by straining and the detours path effect,especially for the case of high injection concentration.In addition,the penetration velocity of red mud particles with high alkalinity is slightly higher than that with low alkalinity.The pore volume at the peak pH is bigger than the pore volume at the peak of the breakthrough curves of red mud filtrate,which indicates that the migration rate of the red mud particles is faster than that of OH-.(6)Comparison of three injections and single pulse injections:In three pulse injections test,the breakthrough curves of red mud filtrate will have a large fluctuation,the peak increases with the injection concentration and flow velocities increases,which is similar to the single pulse injection.The curve of pH changes will also have a large fluctuation,which is affected by the coupling effect of the injection concentration of OH-and the release of OH-from the red mud filtrate.(7)The fitting results of the breakthrough curves show that the dispersivity of the suspended particles increases and the deposition decreases under high alkali conditions.The red mud filtrate has a smaller dispersivity and a higher deposition coefficient than the silica powder suspension.The breakthrough curves of three pulse injection can be well predicted by a single pulse injection,and the Re of fitting curve is above 0.94.(8)Particle recovery:Both the recovery rate and the modal size of recovered particles increase with the increase in flow velocity,and the recovery rate of particles with high alkalinity is higher than that of particles with low alkalinity,which can be attributed to the stronger repulsive interaction between particles and between particles and the matrix induced by OH-.In fact,the recovered particles are smaller at low velocities,because the hydrodynamic force exerted by the flow on the particles is insufficient to mobilize larger particles.