The other side of the question is taken by an operator who states that "Fine-grained fluorspar can be used successfully, but more or less is lost by the draft in the furnace drawing out a good per cent of the finer spar." Another operator believes that fine-grained material can be used successfully and that dusting may be overcome by wetting the fluorspar.

Consumers in the steel trade apparently do not find the small proportion of fines in ordinary gravel spar objectionable, but one operator believes that "Lumps over one-half inch in diameter are a disadvantage, as they require more time and heat for their disintegration and assimilation by the slag." It is therefore apparent that a moderate amount of fines mixed with material up to one-half or five-eighths inch gives the best results, and that there are some disadvantages in using material of 20 mesh or finer exclusively. An attempt was made to briquet the fines produced at Beatty, Nev., but the experiment apparently was unsuccessful.

EFFECT OF IMPURITIES

In basic open-hearth steel practice calcium carbonate is the least objectionable impurity in fluorspar. It in itself is a flux used in the process and is therefore only a diluent which has been bought at fluorspar prices.

Silica is also a diluent but is not a flux, and requires a certain amount of fluorspar to flux it, thus reducing the amount of available fluorspar still further. Usually a maximum of 6 per cent silica is specified in contracts. Fohs 13 states that 1 part of silica requires about 2 parts of fluorspar to flux it, but most eastern producers and consumers figure on 22 parts of fluorspar instead of 2. Using the 22 to 1 ratio and taking as an example an English fluorspar analyzing 76 per cent CaF2 and 17 per cent SiO2, the available CaF, would be 76 per cent - (22X17 per cent 42.5 per cent), or 33.5 per cent; thus a high percentage of silica reduces the value of fluorspar very greatly. (See also p. 77.) In addition, a high silica content requires additional limestone to preserve the basicity of the slag, which is objectionable because a high limestone charge lengthens the time of heat in the furnace with subsequent reduction of tonnage.

A high silica content (above 5 or 6 per cent) is usually penalized by purchasers, but no premium is paid for silica content lower than the standard. The justification offered for this practice is that the man who charges the fluorspar into the open-hearth furnace knows nothing of its quality and uses the same amount whether the

13 Fohs, F. Julius, Fluorspar deposits of Kentucky: Kentucky Geol. Survey Bull. 9, 1907, p. 154.

silica content is high or low. This same argument suggests the impropriety of penalizing high silica and low calcium fluoride content. Furthermore, as Jones 14 points out, the melter in actual practice uses only enough fluorspar to effect the desired results and thus can readily determine the grade of material used. Quality should be standardized and either no penalties exacted or both penalties and premiums paid.

The effect of barium sulphate (barite) is not as clearly understood, but most steel companies in the East object to more than a trace of this material. One western steel mill which regularly uses large quantities of fluorspar containing an average of 5 per cent barite finds it objectionable only as a diluent. This objection is based on two grounds: (1) That the addition of sulphur in any form is a bad practice; and (2) that barite produces a very heavy, viscous slag. The barite thus defeats the purposes for which fluorspar is

used.

The addition of sulphur does not seem to be important, for barite contains only 13.7 per cent sulphur, and if the fluorspar contains 5 per cent barite, 10 pounds (the average charge per ton of steel) would contain only 0.5 pound of barite or 0.0685 pound of sulphur. Even though this all went into the steel, it would add only 0.0034 per cent sulphur to the steel, an amount too small to be taken into account. This very small addition of barite could hardly have an appreciable effect on the viscosity of the slag. Barite, therefore, probably acts chiefly as a diluent. Fohs states that 1 part of fluorspar will flux 11⁄2 parts of barium sulphate.

SUBSTITUTES FOR FLUORSPAR

Most authorities consider fluorspar an essential in the manufacture of basic open-hearth steel. One operator says: "The everincreasing sulphur content of raw materials and fuels necessitates carrying slags of higher lime content, which must be rendered sufficiently fluid for the proper working of heats. The addition of fluorspar makes this possible." Most of the other steel men from whom information was sought agreed substantially with this view, but one held that fluorspar was not always necessary and should be used in moderation. He said that his company used a relatively high proportion of manganese ore in conjunction with a relatively light lime burden, which almost invariably insures a good slag condition, so that ordinarily very little fluorspar is required to adjust the slag. First, it confers fluidity, as well as basicity, to the slag. It tends to prevent absorption of sulphur by iron in all stages of making the heat and to break up FeS when formed. It acts in the

14 Jones, G. H., work cited, p. 4.

latter stages of the heat to deoxidize the bath and to lessen the total amount of nonmetallic inclusions.

Jones 15 points out that high-manganese pig iron increases the fluidity of the slag and therefore decreases the amount of fluorspar necessary for thinning out the slag. However, in some steel-making districts, particularly in the East, pig iron is apt to be high in phosphorus and low in manganese, and it is the general practice where scrap is plentiful and cheap to charge as little pig iron as possible. Iron of this character requires a high lime charge, because the small pig-iron charge, with consequent decreased amount of silicon and manganese, does not tend to create a fluid slag. Large additions of fluorspar are therefore necessary.

No operators consulted knew of any adequate fluorspar substitute that is now in general use or that, in their opinion, could be satisfactorily used at equal or even much increased cost. The most commonly known suggested substitute is calcium chloride, CaCl2, a material now produced chiefly as a by-product in the manufacture of salt from brine or from the Solvay soda process. The output sold in the United States in 1919 was about 74,700 short tons, valued at about $1,043,000, or about $14 per ton. Production as a byproduct is said to be greater than the consumption in present uses. In October, 1922, fused-lump calcium chloride was quoted at $22 to $23 per short ton, f. o. b. cars New York, in car lots.

One operator says:

Calcium chloride is the best-known substitute for fluorspar. It works very well, and permits of carrying a very high lime content in the slag. No records of its use are available, but one authority gives 50 pounds per ton of steel as a good figure, which seems rather high. Compared with our present practice of 6 pounds of fluorspar per ton of steel, the above figure would make the use of calcium chloride, at present prices, prohibitive.

At equal prices per ton, and at a consumption of 10 pounds of fluorspar per ton of steel, according to the above figures, calcium chloride would cost five times as much as fluorspar. Furthermore, calcium chloride is very hygroscopic and deliquescent; that is, absorbs moisture from the air and dissolves, forming a solution. It would therefore be much more difficult than fluorspar to ship, store, and handle.

In the "Saniter" process of desulphurizing, dephosphorizing, and producing a liquid slag, the following mixture per ton of steel is used, according to Harbord and Hall: 16 Dry calcium chloride, 9 pounds; fluorspar, 9 pounds; lime, 15 pounds; and limestone, 8

15 Jones, G. H., work cited. p. 5.

16 Harbord, F. W., and Hall, J. W., Metallurgy of steel. New York, vol. 1, 1916, pp.

192-193.

pounds. As this process uses equal parts of fluorspar and calcium chloride and nearly as much fluorspar as the average in present practice, it can not be considered a substitute for fluorspar.

Other suggested substitutes for fluorspar are lime (CaO), other strongly basic salts such as certain salts of sodium and potassium, iron scale, bauxite, and ilmenite. None of these seem to have been used commercially. Ilmenite (iron titanium oxide (Fe.Ti)2O3) containing 45 to 52 per cent TiO2 is reported to have been used experimentally and is claimed to be slightly more efficient than fluorspar. At present it is not produced in large quantities and sells for $25 to $40 per ton. It is claimed, however, that if substantial markets can be developed a 45 to 50 per cent TiO, product obtained by concentrating titaniferous magnetites can be laid down in the Pittsburgh district for $6 to $7 per ton. Without confirmatory evidence the possibility of substituting ilmenite for fluorspar seems slight, as titanium compounds have always been considered very objectionable in slags, making them heavy and viscous.

In summing up, therefore, fluorspar seems to be essential in the manufacture of steel by the basic open-hearth process. No substitutes have been developed which can compete with fluorspar, even at a greatly increased price. It is used in such relatively small quantities per ton of steel that the cost is almost negligible in comparison with that of the finished steel. Fluorspar will probably continue to be used, therefore, even if mining costs and prices increase appreciably.

FOUNDRY PRACTICE

Fluorspar is used to some extent in iron-foundry practice, usually in lump form, but of gravel grade (No. 2 lump). It is used, as in the open-hearth process, for desulphurizing and dephosphorizing the iron and producing a liquid slag and is of particular value when the iron has a high sulphur content, and when foundries use continuous rather than intermittent melting. In continuous melting the slag must be kept very liquid. It may be added in the cupola or in the ladle before the molten iron is poured. One observer states that in making malleable iron 3 per cent of ground fluorspar in the bottom of the ladle made the iron more malleable and increased the tensile strength by slagging off impurities. In the same way, gray cast iron was made softer without decreasing its wearing qualities. Another writer claims that adding 20 pounds of fluorspar per ton of metal in the cupola brings down the charge more rapidly and makes a thinner slag, hotter iron, and hence sharper castings.

OTHER METALLURGICAL USES

Fluorspar is used as a flux in electric furnaces for making steel, cast iron, and ferro-alloys. The quantity used varies, but probably averages at least 20 pounds per ton of metal.

In smelting refractory ores of gold, silver, and copper, fluorspar has been found very useful as a flux to make a fluid slag. Some writers believe that fluorspar acts on silica to form a silicon fluoride, possibly SiF, which is volatilized. Others believe that the action of fluorspar is largely mechanical, and that a greater part of it is found unchanged in the slag. Examples can probably be cited to prove both contentions and show that, as a matter of fact, the action of fluorspar depends upon the nature of the ore and fluxes, whether the lining is acid or basic, and the type of slag made. It forms fusible compounds with barium and calcium sulphates and assists in fluxing zinc as the sulphide or the oxide. When acid linings are used care should be taken not to use an excess of fluorspar, for rapid corrosion of the lining may result.

In the manufacture of rustless iron of the ferrochromium type in the electric furnace it is reported that iron is first melted and decarburized and then skimmed of slag. The surface of the metal is then covered with a mixture of 75 parts of limestone and 25 parts of high-grade fluorspar. This mixture is melted and preheated to form a bath to which chromite ore and a reducing agent are added. If enough heat has been stored up in the bath the reaction gives off heat and perfect fusion results. The resulting ferrochromium sinks through the slag and alloys with the iron below. This action continues until the iron contains about 12 per cent of chromium.

Fluorspar is used to some extent in smelting lead and silver ores and in refining lead and silver. Here, as in other metallurgical uses, fluorspar has value for its great fluxing properties, its ability to make a thin, fluid slag, its reduction of smelting temperature, and its power to volatilize or slag objectionable impurities.

USE IN GLASS MANUFACTURE

Fluorspar is widely used in manufacturing opal or opaque white glass and colored or cathedral glass. Light opal glass is used for electric, gas, or oil lamp globes, shades, and bulbs for diffusing light; and for vases, bowls, and other ornamental glassware. Dense opal glass is used for containers, such as jars, pots, and bottles, for liquids, foods, and toilet and medicinal preparations. In the form of slabs or plates it is used for table and counter tops, wainscoting, baseboards, shelves, linings for refrigerators, and so on. Some of the opal glasses are sold under trade names, such as "Vitrolite" and "Sani-Onyx."