| It's necessary to take full advantage of the remaining rare earth resources under the background of rare earth shortage around the world which caused by the over-exploitation and the excessive waste,and the rare earth leaching is increasingly of high quantity but with the lower rare earth content.At the situation,the traditional separation methods which are diseconomy and not environment-friendly,like acidic precipitation,solvent extraction,are being replaced by ion exchange,membrane separation and others.The membrane separation technology has been widely used in all fields due to its green and non-secondary pollution etc.advantages.As one kind of this technology,nanofiltration(NF)membrane is also known by folks in recent years,but has rare utilization in rare earth ore.The paper studies the recovery of rare earth form rare earth leachate by NF membranes,aiming to find a new method for rare earth separation and expand the application of the NF membrane technology.Sample of this study is the leaching liquor of ion-adsorbed rare earth ore which comes from Jiangxi,and the NF membranes used in the experiment are one kind of commercial membranes and two kinds of lab-made membranes,all of these membranes are made of polyamide.Results of the study are presented below.(1)This chapter has discussed the effects of operating pressure,feeding flux,p H,operating temperature and volume reduction factor(VRF)on the nanofiltration membranes in the process of rare earth leaching liquor concentration.The experiment result shows that the operating pressure is powerful for nanofiltration membranes and the membrane system has no need to prepressing cause that may decrease membranes' water flux and rejection ration.By compare results in the experiment ensure nanofiltration membranes' water flux after system runs 20 min,within the scope of 0.4 MPa to 1.6 MPa,three nanofiltration membranes' rejection ration are greater than 85% in the 240 min run time,and the suitable operating pressure is in the range of 0.4 MPa and 0.8 MPa.The result shows nanofiltration membranes can keep the better water flux and rejection ration when feeding flux in the scope of 240 L/h and 330 L/h and also find that p H have a little influence of nanofiltration membranes' properties,the suitable operation tempreture ranges 25? to 30?,the VRF has impact on nanofiltraion membrane's water flux and the best value of VRF is three.(2)This chapter has studied the content of rare earth in different operation time after chose the factors.The laboratory finding shows the nanofiltration membrane system can recovery 53.93% of rare earth from the heap leaching after system runs for 240 min.The experimental result also shows that the commercial membrane(NF1)is more suitable for rare earth enrichment and losses of rare earth in the process may accumulate on the membrane's surface and the film hole.And then this experiment also finds that nanofiltratio n membrane may play a role in ammonia nitrogen recycle and environmental protection.(3)The membrane cleaning methods have studied in this chapter.Effects of factors on the membrane cleaning have investigated by orthogonal test,results show cleaning pressure play a key role in the process.Nanofiltration membrane's water flux can recovery about 83.5% with physical cleaning under optimum operating conditions and the water flux recovery may reach up to 96% after the cleaning system runs for 60 min with the 0.1% hydrochloric acid.In practical application,the membrane washing always goes on combine physical cleaning with chemical cleaning.Results of the study have shown that the nanofiltration membrane can be used widely in the rare earth ore with high concentration effective and the commercial nanofiltration membrane(NF1)is more suitable in the operation,furthermore,the ammonia nitrogen in the lixivium has also been concentrated and this technology may be a new method in the ammonia nitrogen recovery. |
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