西南地区典型胶磷矿中稀土元素的赋存特征

Occurrence Characteristics of Rare Earth Elements in Typical Collophanite in Southwest China

采用化学选择性浸出方法对沉积型胶磷矿中稀土元素的赋存状态进行研究。研究发现沉积型磷矿主要由碳酸盐相、磷酸盐相和硅酸盐相三相组成。各相最佳分相反应条件为:碳酸盐相控制乙酸浓度0.3%~0.5%,浸出温度为60℃,浸出时间90 min,分步浸出两次;磷酸盐相浸出条件是在10%~20%硝酸,浸出温度为60℃,浸出120 min,硅酸盐相采用四酸(盐酸、硝酸、氢氟酸及高氯酸)消解。结果表明,沉积型磷矿(昆阳、晋宁、贵州)中稀土元素少量以独立矿物的形式存在,主要以类质同像存在于磷灰石中,磷灰石中稀土含量占总量的98%以上,主要是Ce,Nd,La等轻稀土元素及Y,其次是Pr,Sm,Gd,Dy。轻稀土元素总量与重稀土元素总量比值(∑LREE/∑HREE)为2.5~5.5,体现了轻稀土富集、重稀土亏损的特征。碳酸盐(白云石)及硅酸盐(石英为主)中稀土含量极低。碳酸盐相的高效选择性浸出,将大幅降低钙、镁杂质进入后续磷肥生产工序,降低除杂工序难度。磷矿中的稀土作为一种潜在的资源,查清磷矿中稀土赋存状态对开展综合回收具有重要意义。

Besides independent rare earth deposits,there are a large part of the apatite and phosphorite ore symbiosis in nature that contain rare earth elements,such as Russia is rich in phosphate reserves which have high grade and high rare earth content,the representative one is the Kola Peninsula(Kola)phosphate resources,the rare earth content is close to 1.0%.The total amount of rare earth associated with phosphate in the world is 50 million tons on assumption of the world’s total phosphate reserves are about 100 billion tons and the average rare earth content is 0.5‰.In Yunnan,Guizhou,Sichuan,Hunan etc.,there are abundance of phosphate resources,among which Yunnan and Guizhou have oversize phosphate sedimentary deposit with low to medium grade,the phosphorite reserves is about 1.6 billion tons,according to estimation of the content of rare earth of 0.5‰~1‰,the associated rare earth reserves of more than 700,000 tons,among of which yttrium occupies about 35%,praseodymium neodymium accounted for about 20%,terbium,dysprosium accounted for 2%~5%,which is the reserve resource of middle and heavy rare earth after the ionized ore.Phosphate ore contains more than a dozen of valuable elements such as rare earth,it is a potential resource of rare earth.It is of great significance to study the existence of rare earth elements in phosphate ore for the comprehensive utilization and development of the resources.Kunyang phosphate mine is a collophane,includes micro-fine grained apatite,dolomite,quartz,chalcedony,a small amount of pyrite,limonite,rutile,hydromica and other clay minerals and feldspar,trace chalcopyrite,barite and other minerals,is a very important phosphorus resource deposit in China.Collophanite is usually in the form of granular debris,nodule and oolitic,and has recrystallized fine-grained apatite during and after diagenesis.Based on the mineral composition of Kunyang phosphate deposit,sedimentary collophanite can be divided into three phases:carbonate phase,phosphate phase and silicate phase.The phase separation approach is drawn up as carbonate phase,phosphate phase and silicate phase selectively leached by chemical reagents in sequence.A series of reagents hydrochloric acid,nitric acid,perchloric acid,citric acid and acetic acid were selected to carry out the selective leaching of carbonate.The optimum conditions of phase separation reaction were listed as follows:carbonate phase controlled acetic acid concentration of0.3%~0.5%,leaching temperature of 60℃,leaching time of 90 min,leaching twice,phosphate phase controlled nitric acid of 10%~20%,leaching temperature of 60℃,the silicate phase was digested by tetraoic acid(hydrochloric acid,nitric acid,hydrofluoric acid and perchloric acid)after leaching for 120 min.The result showed that a small amount of rare earth elements existed in the form of independent minerals in sedimentary phosphate rock of Kunyang,Jinning County and Guizhou,mainly existed in apatite as isomorphism.The content of rare earth in apatite was more than 98%,mainly Ce,Nd,La and Y,followed by Pr,Sm,Gd and Dy.The value of∑LREE/∑HREE was between 2.5 and 5.5,which showed the enrichment of light rare earth and the depletion of heavy rare earth,the rare earth content in carbonate(dolomite)and silicate(mainly quartz)was very low.The high-efficient selective leaching of carbonate phase would greatly reduce the calcium and magnesium impurities into the subsequent phosphate fertilizer production process,reducing the difficulty of impurity removal process.As a potential resource,finding out the existing state of rare earth in phosphate rock was significant for comprehensive recovery.