Study On Preparation Of Calcium Sulfate Whiskers By Rare-Earth Gypsum Under Normal Pressure Acidification And Related Modification

In the hydrometallurgical process of mixed rare earth ore,the presence of calcium element will have a certain effect on the extraction of single rare earth.The chemical precipitation method is used to remove the calcium element in the rare earth chloride solution.In order to make full use of the calcium element in Bayan Obo rare earth ore,this article conducted a comprehensive utilization study on the calcium slag generated during the treatment of rare earth chloride solution.On the basis of previous achievements,we can prepare calcium slag into calcium sulfate whiskers,and we have also studied the subsequent modification of calcium sulfate whiskers.The calcium sulfate whiskers can be used in friction materials,filling materials,filter materials,etc.Calcium sulfate whiskers were synthesized by atmospheric pressure acidification using rare earth-containing gypsum as raw material.The effects of different process conditions on the morphology of the formed calcium sulfate whiskers were investigated.At the same time,the effects of the type of crystal growth promoter and the content of crystal growth promoter on the growth of calcium sulfate whiskers were also investigated.The surface morphology and phase characteristics of calcium sulfate whiskers were characterized by SEM and XRD,respectively.The experimental results show that the optimal reaction conditions for preparing calcium sulfate whiskers are rare earth gypsum concentration 0.22g/mL,reaction time 25min,hydrochloric acid concentration 2.8mol/L,reaction temperature 70°C,and aging time 4h.The average length of the calcium sulfate whiskers synthesized under these conditions is 61?m,and the average aspect ratio is 30.5.CuCl₂ was selected as a growth promoter for promoting the growth of calcium sulfate whiskers by contrast experiments.At the same time,it can be seen from the comparative test that a small amount of rare earth in the rare earth gypsum plays a positive role in the growth of calcium sulfate whiskers.With the addition of 0.5%CuCl₂,the aspect ratio of calcium sulfate whisker was increased from 30.5 to 41,and the length was increased from61?m to 81?m.The surface modification of the calcium sulfate whisker was studied.Inorganic-organic modification of calcium sulfate whiskers with lauric acid and sodium tungstate was carried out.The effects of a series of modification conditions on the hydrophobic and lipophilic properties of calcium sulfate whiskers were investigated.XRD,SEM,FT-IR,XPS and contact angle characterization and experimental results show that the modifier is 15%,the modification time is 15min,the modification temperature is 60?,and the slurry concentration is 10%,the concentration of sodium tungstate is 1.0mol/L,the contact angle of the modified product is the largest,reaching 121°,and the modification effect is good.The modification mechanism is that lauric acid and sodium tungstate react with the surface of calcium sulfate whiskers to form a hydrophobic layer attached to the surface of the whiskers,so that the surface properties of calcium sulfate whiskers change from hydrophilic to hydrophobic.