| Nickel and cobalt are important strategic metals,and play important roles in the industry production.Because of the very similar physical and chemical properties,these two metals are always symbiotic and associated in the deposits or secondary resources.It is an important problem for the separation and recovery of nickel and cobalt from leachate before the refining process,and also is one of the most difficult operations in hydrometallurgyprocessing.Toovercometheproblemsexistedin conventional solvent extraction,such as long distance and small driving force of mass transfer,and difficult for the accurate and quantitative metering etc.,a new extraction in microreactors was introduced in this thesis.The liquid-liquid phases were divided into microscale or even nanoscale fluids in the microchannels,and physical gradients of pressure,temperature,density,and concentration increased obviously.The mass transfer distance between phases was shortened,and the surface area and drivingforcewereenhancedprominently.Therefore,extractionin microreactors had prominent advantages,such as small size footprint,rapid mixing through micro channel structure without mechanical agitation,short contact time,high efficiency of extraction and separation,high mass transferperformance,uniformresidencetimedistribution,andno emulsification,etc.Three representative microreactors,i.e.the slit interdigital micromixer?SIM?with multi-layer flow,coiled flow inverter?CFI?with segmented flow,and 3D converg ing-diverging microreactor?3DM?with chaotic convective flow,were applied for the extraction and separation of cobalt and nickel,and the effects of different processing and structural parameters were also studied.The main research contents and obtained results were as follows:?1?Extraction and separation of cobalt and nickel by P507 in SIM.Liquid-liquid two phases were divided into n interaction thin layers through the slit interdigital microchannel structure,and thickness of the micro flows was only tens of micrometers or even smaller,so mass transfer between two phases was greatly enhanced.Effects of final p H and contact time on extraction and separation of Co and Ni in SIM were studied,and compared with the results in conventional batch extraction in parallel.The results were shown that compared with conventional batch extraction,for20%v/v P507 with 70%saponification ratio,the residence time in SIM was reduced from 5 min to 9.6 ms,single stage extraction ratio of Co was increased from 72.5%to 85.5%,and separation factor between Co and Ni was enhanced from 14.3 to 30.4.Quantitative extraction of Co?>99.9%?was achieved in four stages in SIM,but that was seven in batch.The extraction and separation performance of cobalt and nickel in SIM microreactors was greatly improved.k La values of Co and Ni in SIM were13.7575.2 s-11 and 24.8168.7 s-1,respectively,which were three or four orders of magnitude higher than that in batch experiments which the values were?3.319.9?×10-33 s-11 and?1.911.4?×10-33 s-1,respectively.In addition,the results from regeneration and recycle using P507 loaded organic phase was shown that the single back extraction ratio of Co and Ni were 99.5%and 98.9%,respectively,which was better than the results in conventional back extraction,and the structure of the regenerated organic phases were stable.?2?Extraction and separation of cobalt and nickel by Cyanex272 in CFI.Effects of final p H,contact time,and extractant concentration on extraction and separation of Co and Ni in CFI were studied,and compared with the results in conventional batch extraction in parallel.The results were shown that at 59 s residence time and 15%v/v Cyanex272 with 40%saponification ratio,separation factor between Co and Ni was 775 in CFI,which was two times higher than that of 383 in conventional batch extraction.Segmented flowswereformedwhenliquid-liquidphasespassedthroughthe microchannel,and mass transfer between two phases took place through internal circulation within each slug and diffusion between adjacent slugs.The helically coiled tube coupling with 90°bends in CFI were specially favourable for the longitudinal and radial mixing and mass transfer of liquid-liquid segmented flows.Comparing with the unstructured straight capillary microreactor,separation efficiency was greatly enhanced in CFI.k La values of Co and Ni were 0.0170.256 s-11 and 0.0040.057 s-1,respectively,andthedeviationofoverallvolumetricmasstransfer coefficients between Co and Ni was 4.5 times,which was much higher than that in batch,where it was just 1.62 times.?3?Extraction and separation of cobalt and nickel by Cyanex272 in3DM.The 3D converging-diverging conical structure produced complex three dimensional internal circulation flows as the effect of mechanical agitation,and the mass transfer was strengthened by chaotic convection.The special 3D structured microchannel was favourable for the reduction of pressure drop and energy dissipation?.The Co extraction efficiency was reached up to 99%,separation factor between Co and Ni was 1367 at 9 s residence time by 12.5%v/v Cyanex272 with 40%saponification ratio.99.8%of Co was extracted into organic phase by two counter-current stages.k La values of Co and Ni were 0.0111.20 s-11 and 0.00060.13 s-1,respectively.The deviation of overall volumetric mass transfer coefficients between Co and Ni was as high as 18 times.According to the calculation data of the specific area of the regular segmented flows,the overall mass transfer coefficient k L of cobalt and nickel were?0.9912.88?×10-55 m·s-1and?0.212.84?×10-55 m·s-1,respectively.In summary,compared with conventional macro-scale reactors and unstructured straight micro-channel reactors,in above three structured microreactors,the higher extraction ratio of Co and separation factor between Co and Ni and higher mass transfer performances had been achieved at shorter residence time.Meanwhile,because of the simple geometry and easy scale-out by parallelization of the microchannel modular,and the highest overall volumetric mass transfer coefficient deviation between Co and Ni,3DM had more promising application prospect for the extraction and separation of cobalt and nickel in hydrometallurgy. |
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