不同岩石风化产物La^(3+)吸附特性对稀土成矿的启示

Enlightenment of Characteristics of La^(3+)Adsorption on Different Rock Weathering Products on Rare Earth Mineralization

稀土元素在不同岩石风化产物上的吸附特性与离子型稀土的富集成矿存在某种联系。为探究该种联系,以La^(3+)为吸附质,以江西寻乌(火山岩型)、安远(混合岩型)两种不同矿床类型的离子型稀土矿为吸附剂,考察了不同氯化镧浓度(0.1,0.4和0.8 g·L^(-1))下La^(3+)在两种不同岩石风化产物上的吸附特性。将La^(3+)吸附量与两种稀土矿配分特点、颗粒表面性质关联,探讨了稀土矿富集特点,为稀土矿成矿机制的研究提供启示。结果表明:(1)两种稀土矿La^(3+)吸附量并非与氯化镧浓度成正比,存在最大吸附量,对应氯化镧浓度为0.4 g·L^(-1)。(2)不同稀土矿对La^(3+)吸附存在差异,该差异性由颗粒表面电位主导,表面电位绝对值越大,La^(3+)吸附量越大。(3)La^(3+)在寻乌、安远矿的吸附主要以可交换态为主,相较而言,寻乌矿与La^(3+)的“亲和力”更强,更易形成特异性吸附。这种特异性吸附与不同稀土矿的富集模式存在某种关系,即稀土矿富集模式的不同可能因RE^(3+)与不同岩石风化产物的亲和力不同所致。

The adsorption characteristics of rare earth elements on different rock weathering products are related to the enrichment of ion-absorbed type rare earth.To provide enlightenment for the study of rare earth mineralization mechanism,the adsorption characteristics of La^(3+)by two kinds of ion-absorbed type rare earth ores were analyzed.Through correlating the adsorption amount of La^(3+)with partition characteristics,specific surface area of particles and surface charge properties of ores,the enrichment mechanism of rare earth ore was discussed.Firstly,the adsorption experiment of La^(3+)on kaolin was carried out.Lanthanum chloride solutions with concentration of 0.025,0.05,0.075,0.1,0.15,0.2,0.25,0.3,0.4,0.45,0.5,0.6,0.8,1 g·L^(-1)were prepared.Kaolin and lanthanum chloride solutions were added according tosolid-liquid ratio of 1∶5,and then placed on a magnetic stirrer(300 r·min-1,30℃)for 4 h.Concentration of La^(3+)in the supernatant was determined by Arsenazo III spectrophotometry.Relationship between the initial concentration of lanthanum chloride and the adsorption capacity of La^(3+)was analyzed.Secondly,the initial concentrations of lanthanum chloride were determinedby referring to the concentration corresponding to adsorption amount of La^(3+)rising,steady and re-rising on Kaolin.According to the solid-liquid ratio of 1∶5,lanthanum chloride solutionand dry ore samples which from Xunwu(volcanics weathering products)and Anyuan(migmatite weathering products)were added respectively.The particle size of ore samples was-0.1 mm.Adsorption and test process as before.When ores were not saturated,separated supernatant and added lanthanum chloride with the same initial concentration,repeated the above operation.Adsorption capacities of La^(3+)on these two ores were compared,and partition,specific surface area and surface potential of ores were tested.Finally,the adsorption form and content of La^(3+)adsorbed on these two ores were analyzed through desorption test.Adsorption of La^(3+)on kaolin can be divided into three stages:rising stage,stable stage and re-rising stage.As initial concentration of lanthanum chloride<0.3 g·L^(-1),adsorption amount of La^(3+)increased with concentration of lanthanum chloride,while lanthanum chloride from 0.3 to 0.5 g·L^(-1),adsorption amount of La^(3+)remained stable,but as lanthanum chloride>0.5g·L^(-1),adsorption amount of La^(3+)increased again with concentration of lanthanum chloride.Lanthanum chloride concentrations of 0.1,0.4 and 0.8 g·L^(-1)were determined as the initial concentration in the adsorption test of Xunwu ore and Anyuan ore.As lanthanum chlorideinitial concentration of 0.1 g·L^(-1),amounts of La^(3+)adsorption on these two ores were stable first,then decreased,and then stable again with the increase of adding times of lanthanum chloride solution.However,as lanthanum chlorideinitial concentration of 0.4 or0.8 g·L^(-1),amounts of La^(3+)adsorption on these two ores were decreased rapidly first and then stable.The decrease rate of La^(3+)adsorption capacity with the addition of solution showed that Anyuanore was far greater than Xunwu ore in the early stage,and the later Xunwu ore was slightly greater.The final adsorption amount of La^(3+)was QXunwu>QAnyuan,and QXunwu≈2QAnyuan.Adsorption amount of La^(3+)was not proportional to the initial concentration of lanthanum chloride,and there was a maximum adsorption with initial concentration c0=0.4 g·L^(-1).The specific surface area:Anyuan ore>Xunwu ore;Absolute value of surface potential:Xunwu ore>Anyuan ore.Desorption test showed that the amount of water-soluble La^(3+)3+3+adsorbed on Xunwu ore with lanthanum chloride initial concentration of 0.1 or 0.8 g·L^(-1);while for lanthanum chloride initial concentration of 0.4 g·L^(-1),amount of water-soluble La^(3+)3+3+adsorbed on Xunwu ore;but for Anyuan ore,with any of the three lanthanum chloride initial concentrations,La^(3+)adsorption capacity:water-soluble3+adsorbed on these two ores were mainly ion-exchangeable and fixed.Several conclusions were listed as following:(1)Adsorption amount of La^(3+)on these two ores were not directly proportional to the lanthanum chloride concentration,amaximum adsorption amount of La^(3+)was expected at lanthanum chloride concentration of 0.4 g·L^(-1).The reason why La^(3+)adsorbed on kaolin"step by step"might be due to the unsaturated adsorption on the kaolin surface,instead of forming colloidal phase La as the lanthanum chlorideincreases to a certain extent.(2)Adsorption capacity of La^(3+)on different rare earth ores were different,which was dominated by surface potential of particles.The greater the surface potential,the greater the adsorption capacity of La^(3+).There was no direct relationship between the specific surface area and the adsorption amount of La^(3+),not that the larger the specific surface area,the adsorption amount of La^(3+).(3)Forms of La^(3+)adsorption on these two ores were mainly ion-exchangeable.In comparison,adsorption capacity of La^(3+)on Xunwu ore was stronger than Anyuan ore,and more ion-exchangeable La^(3+)and fixed La^(3+)were formed on Xunwu ore.According to the electric double layer theory,the fixed La^(3+)are closer to the surface of the particles than the ion-exchangeable La^(3+),more affected by the electric field on the surface of the particles.Therefore,the affinity of Xunwu to La^(3+)was greater than that of Anyuan,which made it easier to form specific adsorption than Anyuan ore.This specific adsorption was related to the enrichment pattern of different rare earth minerals,that was,different enrichment pattern of rareearth minerals might be caused by different adsorption capacity of RE3+on different rock weathering products.