硅酸盐矿物微量化学分析

用微量技术进行化学分析,可以比一般的常量技术大大节省矿物样品消耗,较早的硅酸盐矿物微量分析方法能够取得准确的全分析结果,但是要求很高的个人实验技术,而且方法已经过时。国内目前流行的少用样品的方法误差过大,不能适应地质科学研究要求。本文提出一个比较准确而又不要求分析人员具有特殊技术训练的实用有效的微量化学分忻方法,其中只使用一般化验室的常用设备。 这个分析方法包括SiO_2、Al_2O_3,Fe_2O_3,FeO,MgO,CaO,Na_2O,K_2O,H_2O+、H_2O、P_2O_s、TiO_2,MnO,BaO和F,共15项目。方法中保留必要的系统分析以节省样品,采取充分利用称样的方法简化操作技术,同时保证容量法有足够的准确度。全分析共消耗矿物65mg。此方法中SiO_2和BaO禾用重量法,Al_2O_3、Fe_2O_3T、MgO和CaO采用容量法。文中比较详尽地描述了分析技术,对于已有硅酸盐经典分析经验的分析人员不难掌握。除了将常用的比学分忻方法实行微量化以外,对于SiO_2,H_2O+、F等项目采用新的微量方法和仪器,对于Fe_2O_3和Al_2O_3用同一份溶液成功地实行连续测定,节省了样品。 此方法节约试剂,操作迅速,已成功地用于分析多种硅酸盐矿物(白云母、黑云母、角闪石,石榴子石、斜长石)。

THE MICROCHEMICAL ANALYSIS OF SILICATE MINERALS

The present paper suggests a practical microchemical method for the analysis of silicate minerals .Delicate micro techniques have been reduced to a mininum in the method,it does not require a special training of the analyst. Classical gravimetric and volumetric methods are used for the determination of most major constituents. Larger aliquots are used to simplify titration operations and an improvement in accuracy is gained as well. Most procedures are the scaling down of approved macro methods, except that of SiO2, H2O +and K, in -which new micro procedures and apparatus have been applied to improve the performance. The complete scheme uses five separate portions of sample and consumes 65 mg of material in the analysis for fifteen common constituents- SiO2, A12O3, Fe2O3, FeO, MgO, CaO, Na2O, K20, H2O + , H2O-, P2O5, TiO2, MnO, BaO and F. 1. The main portion (29 mg): The sample is dried at 105-110C to obtion H2O-. To determine Si02, the dried sample is fused with sodium carbonate, dehydrated once with hydrochloric acid on a water bath, followed by polyethylene oxide coagulation to recover the residual silica. The silica precipitate is collected on a small filter paper and determined by gravimetry. K2O3 is precipitated twice with ammonia ironi the silica filtrate. The precipitate is dissolved in dilute sulfuric acid after pyrosulfatc fusion.A single aliquot is used to determine Fe2O2T and A12O3 by consecutive EDTA titration. TiO2 and P2O5 are determined in other aliquots by spec-trophotometry. CaO and MgO are determined by complexometry in aliquots of the filtrate from R2O3,MnO is determined by spectrophotometry in another aliquot. 2. Combined water (10 mg) : H2O is determined by Penfield method. A specially designed micro Penfield tube is used to obtain accurate results. 3. FeO (10 mg):: The sample is decomposed in a boiling mixture of hydrofluoric and sulfuric acids, followed by bichromate titration. 4. Na2O, K2O and BaO (20mg): The sample is decomposed by hydrofluoric and sulfuric acids, followed by repeated evaporation with sulfuric acid to remove fluorine. Barium is converted to insoluble sulfate and separated as a white residue in the above treatment. The sulfate is collected on a filter, and weighed as BaSO4. The alkalis are determined in the filtrate by flame photometry. 5. F (5mg). The sample is decomposed by Na2CO3+ZnO fusion. The water extract is subjected to steam distillation in the presence of sulfuric acid. Fluorine is determined spectrophotometrically by Zr-ECR method. A new micro distillation apparatus is developed, which works efficiently and rapidly. The method has been successfully applied to the analysis of various silicate minerals, such as muscovite, biotite, hornblende, garnet and plagio-clase.