Of nepheline

Hafnium had lain hidden for untold centuries, not because of its rarity but because of its dose similarity to zirconium (16), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, C. F. Rammelsberg, A. E. Nordenskjold, J.-C. G. de Marignac, and other experts on the chemistry of zirconium, he found that they contained from 1 to 5 per cent of the new element (26, 27). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (24, 28). Some of the minerals were of nepheline syenitic and some of granitic origin (20). Hafnium and zirconium are so closely related chemically and so closely associated in the mineral realm that their separation is even more difficult than that of niobium (columbium) and tantalum (29). The ratio of hafnium to zirconium is not the same in all minerals. 

Hamilton, J. P., Brantley, S. L., Pantano, C. G., Criscenti, L. J. Kubicki, J. D. 2001. Dissolution of nepheline, jadeite and albite glasses Toward better models for aluminosilicate dissolution. Geochemica et Cosmochimica Acta, 65, 3683-3702. 

Immense masses of nepheline-rich rocks occur on the Kola Peninsula, the former U.S.S.R., in Norway and in the Republic of South Africa also in the Bancroft, Ontario, Canada region. Smaller deposits are found in Maine and Arkansas in the United States. Fine crystals are found in lavas on Mt, fesuvius, Italy. 

Figure 10.26. (a) A projection along c of nepheline (KNa3Al4Si4Oi6). Tetrahedra of Si04 (up) and A104 (down) alternate around the rings at the corners. (b) A side view of the cell. 

We mentioned earlier that the true symmetry of the unit cell may not simply be manifested macroscopically upon infinite translation in three dimensions. Buerger has illustrated this with the mineral nepheline, (Na,K)AlSiC>4 (Buerger, 1978). The true symmetry of the nepheline crystal lattice, the symmetry of the unit cell, consists merely of a sixfold rotation axis (class 6) as would be exhibited by a hexagonal prism with nonequivalent halves. That is, there is no mirror plane perpendicular to the rotation axis. However, the absence of this mirror plane is obviously not macroscopically visible in the hexagonal prism form development of nepheline, implying a higher apparent symmetry (6/mmm). 

Several other anhydrous calcium aluminosilicates are known, including grossular or garnet (C3AS3), which is a high-pressure phase, various dehydration products of zeolites, and various products formed metastably by crystallization from melts or glasses. Most are too acid in composition to be of clear relevance to cement chemistry, but some of the devitrification products, especially those with compositions near to CA and structures similar to those of nepheline (Na3KAl4Si40i6) or kalsilite (KAlSiOj (Y4), are of possible interest in relation to the formation of calcium aluminate cements. 

Also common is the mechanical destruction of refractories resulting from reactions with melts or vapours and gases producing new crystalline phases with substantially different density or thermal expansion. One example is the oxidation-reduction reactions of materials containing higher amounts of iron oxides, or the formation of nepheline by the effect of alkali bn mullite, sillimanite and other materials. These reactions are responsible for spalling of the affected layers. 

High-temperature Na MAS NMR has been used to study the exchange of Na among the alkali sites of nepheline ([Na,K]AlSi04) at 500°C (Stebbins et al. 1989). These materials are of interest because they display ionic conductivity. The Na exchange rates estimated from the temperature-dependent changes in the Na NMR spectra are consistent with the correlation times derived from cation diffusivity measurements. 

The authors summarized the results of the soda reaction test as follows For the high-silica samples the reaction products were identified as nepheline and sodium aluminum silicate (3 2 4). The amount of nepheline decreased with increasing alumina content, whereas the amount of (3 2 4) compound increased. The lack of silica in the high alumina samples permits the free alumina not tied up as a sodium aluminum silicate to react with the alkali to form beta-alumina. Higher amounts of soda produce sodium aluminates. 

In the model systems C through I (Table II) different sources of calcium and sodium were mixed with clay (kaolinite) and heated to observe their role in forming the aluminosilicates typical of ash fouling deposits. In systems C and D calcium acetate and sodium acetate were mixed with kaolinite in equal molar ratios. X-ray diffractometer patterns showed that both systems were, for the most part, amorphous at 750°C. However, in system E where sodium and calcium acetate were present in equal molar ratios carnegietite was formed at 750°C. Carnegietite is a polymorph of nepheline. In carnegietite the sodium cation is tetrahedrally coordinated whereas in nepheline the sodium cation is octahedrally coordinated. 

Tole, M.P., A.C. Lasaga, C. Pantano, and W.B. White. 1986. The kinetics of dissolution of nepheline (NaAlSiO4). Geochim. Cosmochim. Acta 50 379-392. 

Figure 1 shows the adsorption capacity of a Type 4A zeolite at the end of thermal treatment. The water adsorption capacity lessens starting at 550°C and falls abruptly from 620° to 670°C. The x-ray diffraction patterns of the samples treated from 450° to 670°C are characteristic of pure Type 4A zeolite. When a sample is treated at 740°C, lines characteristic of low form camegieite appear. After treatment at 790°C, the pattern indicates the presence of a small amount of zeolite, a large proportion of low form camegieite, and a very small quantity of nepheline. After treatment at 850°C, nothing remains except low form camegieite and nepheline in small proportions. 

Nepheline syenite Mixture of nepheline and feldspars Varies with exact composition... 

At 0%, the resistance value of a thick film composed solely of glass is displayed and at 100%, those of a sintered pullet composed of beta-alumina only, of sintered pullet of sodium sulfate and a sintered pullet of nepheline, prepared for this study. 

Major suppliers of feldspar include Franklin Limestone Co. KMG Minerals Inc. Spartan Minerals Corp. and Unimin Specialty Minerals Inc. Major suppliers of nepheline syenite include Unimin Specialty Minerals Inc. 

Nepheline Syenite. An igneous rock composed principally of nepheline (K20.3Na20.4Al203.8Si02) and feldspar. There are large deposits in Ontario (Canada), and Stjernoy (Norway). It is used as a flux in whiteware bodies, and as a constituent of some glasses and enamels. 

Figure 2-8 TEM/replica of nepheline-kalsilite interface showing growth of kalsilite around edge of each nepheline crystai. Direction of K+ Na+ is from lower right to upper left, (bar = 1 jim).

Kubo, Y., Yamaguchi, G., and Kasahara, K. (1966) Inverted phase relation in the formation of nepheline and camegieite from the system kaolinite-sodium carbonate. Am. Mineral, 51, 516-521. 

Another source is non-bauxitic raw materials such as nepheline Na3K(AlSi04)4 and alunite KAl3(S04)2(0H)6. At the moment 4 major bauxite mines and 2 nepheline sources/mines are in operation in Russia. The AI2O3 content is substantially lower than in bauxite ores and in order to produce 11 of Al, usually 3-41 of bauxite is enough, while 7-8 t of nepheline and alunite are needed. Nevertheless, nepheline ore is a part of apatite-nepheline, nepheline sienite and urtite deposits. It enables complex process with nepheline concentrate used for alumina and apatite concentrate for fertilizers production. Alunite is also complex source, containing alumina, sulfur anhydrite and alkali Na and K metals. Once again, all those elements may be definitely detected and controlled by online LIBS technique. 

Nepheline, an aluminium silicate of ideal composition (Na,K) AlSi04, is a mineral which may be white, grey, brown, brownish grey, or reddish white due to the presence of impurities. The name derives from the Greek nephele, cloud , because it becomes clouded when put in strong acid. It occurs as a component of nepheline syenites q.v.), which have been used as pigments. 

As component of nepheline syenites (used as fillers and extenders)... 

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