Swelling Inhibition Mechanism And Process Enhancement Of Weathered Crust Elution-Deposited Rare Earth Ore With CMCS

Weathered crust elution-deposited rare earth ore have great commercial value because they are rich in medium and heavy rare earths.The rare earths are mainly adsorbed on clay minerals in the form of hydrated or hydroxyhydrated ions,and can only be mined by ion exchange.In the process of in-situ leaching of rare earth,the swelling of clay minerals can easily lead to landslide geological disasters,resulting in the leakage of leaching agent ammonium sulfate and rare earth,destroying farmland in mining areas,causing serious environmental pollution,and affecting the personal safety and economic benefits of mines.In order to prevent the occurrence of landslides during in-situ leaching of rare earth ore from the source,carboxymethyl chitosan(CMCS)was used as anti-swelling agent and the newly discovered weathering crust elutiondeposited rare earth ore in Yunnan Province was taken as the research object.through dynamic linear swelling test,and with the help of modern analytical techniques to reveal the mechanism of CMCS swelling inhibition.A composite leaching agent composed of CMCS and ammonium sulfate was used to investigate the effects of carboxymethyl chitosan concentration,leaching temperature,flow rate,pH and other factors on the leaching kinetics and mass transfer process of rare earth through the leaching test of inhibiting swelling.In order to optimize the leaching process parameters,establish rare earth leaching kinetic model,strengthen the leaching process,reveal the leaching mechanism of rare earth,and provide theoretical basis and technical support for the safe and efficient development and utilization of weathering crust elution-deposited rare earth ore.The main findings are as follows:(1)The content of all-phase rare earths in Yunnan weathering crust elution-deposited rare earth ore is 0.247%,and the content of ionic phase rare earths is 0.225%.The order of rare earth content in different occurrence states in this ore is:ionic phase>mineral phase>colloidal phase>>water soluble phase.The weathering crust elution-deposited rare earth ore will gradually remove the adsorbed water,interlayer water and structural water in the ore in the process of increasing the temperature from 30℃ to 700℃,and the ore contain more water.(2)CMCS with different molecular weights has the effect of inhibiting swelling of montmorillonite and rare earth minerals,and is better than the conventional inorganic swelling inhibitor KCl,and with the increase of CMCS concentration,the swelling inhibition performance of MMT and rare earth minerals gradually increases.CMCS with molecular weights of 20000 and 300000 has better swelling inhibition performance.The swelling inhibition mechanism of CMCS is that CMCS has certain hydrophobic and polar groups,which coat the clay particles to form a polymeric film to avoid the intrusion of water,thereby inhibiting the swelling of clay minerals.In addition,the CMCS skeleton can be embedded in the clay interlayer to form a single-layer orientation,thereby draining the internal water and further preventing the clay from swelling.Based on the results of the column leaching test and the economic cost analysis,CMCS with a molecular weight of 20000 and a concentration of 0.1 wt%was selected for the follow-up test.(3)The study of column leaching kinetics shows that increasing the leaching temperature,ammonium concentration or flow rate can increase the leaching rate of rare earth within a certain range.The leaching agent pH in the range of 5～8 has little effect on the rare earth leaching rate.The leaching process of rare earth ions is controlled by internal diffusion kinetics,the activation energy of the leaching reaction is 9.58 kJ/mol,and the reaction order is-0.3519.The kinetic equations for temperature and concentration are constructed as:1-2/3α(1-α)2/3=2.3331·C0-0.3519·e-9580/8.314T·t.(4)The study of the mass transfer process of column leaching shows that the relationship between the flow rate u and the height of the theoretical plate(HETP)conforms to the Van Deemter equation.There is an optimal flow rate(0.15mL/min),which makes the rare earth leaching HETP minimum and the rare earth leaching mass transfer efficiency the highest.When the CMCS concentration is lower than 0.1 wt%,increasing the CMCS concentration can reduce the rare earth leaching HETP,thereby improving the rare earth mass transfer efficiency;when the temperature is lower than 303.15 K,increasing the temperature can reduce the rare earth leaching HETP,thereby improving the rare earth mass transfer efficiency.0.1 wt%CMCS(20000)and 2%ammonium sulfate are combined to form a new composite leaching agent.The rare earth ore is leached at a temperature of 303K,a flow rate of 0.15 mL/min,and a pH of 6.50.The rare earth leaching rate can reach 99.11%.Meanwhile,the linear swelling height of rare earth minerals is 1.35mm,which is better than that of single ammonium sulfate leaching agent.The composite leaching agent can inhibit the swelling of clay minerals,effectively prevent the occurrence of geological disasters such as landslides,and does not affect the leaching of rare earths,which is helpful to realize safe and efficient mining of weathered crust elution-deposited rare earth ore.