US2752236A - Method of recovering tin from in bearing materials - Google Patents

Description

United States atet METHOD OF RECDVERING TIN FROM TIN BEARING MATERIALS Lyall J. Lichty, Ottawa, Ontario, Canada, assignor to Quebec Metallurgical Industries Limited, Toronto, Gntario, Canada, a company of Canada No Drawing. Application September 13, 1952, Serial No. 309,548

3 Claims. (Cl. 7585) The present invention relates to the recovery of tin from tin bearing materials, such as ore, slag and concentrates.

The literature on the metallurgy of tin indicates that the smelting of tin ore has presented great difficulties. Thus, C. L. Mantell in his book entitled Tin, second edition, Reinhold Publishing Corporation, New York, 1949, indicates the following ditficulties. It states that tin oxide readily combines with silica to form tin silicates. Consequently, a considerable amount of tin invariably goes into the slag in the form of readily fusible tin silicates mixed with other complex silicates which make up the slag. On the other hand, if an extremely basic slag is used, tin oxide will act as an acid and enter the slag. Slag produced in the first-run smelting of tin concentrates invariably contains so much tin that it must be retreated before being discarded. Smelters can handle foul Bolivian ores only with great ditficulty. Millions of tons of low-grade ore thus far have no commercial value.

The prior art also indicates that silicon is not an eflective reducing agent for the reduction of tin from its ores and slag. Thus, the United States patents to Lamy No. 1,518,742 and to Lamy and Gagnaux No. 1,826,552 describe processes for recovering tin from its ores or from slag containing tin by reduction with a suitable reducing agent which is not identified. In addition to the reducing agent, silicon or ferrosilicon is added for the purpose of combining with and acting as a collector of iron. The tin and the ferrosilicon separate on cooling owing to their diiferent densities. The process of the latter patent diifers from the former in that the composition of the added silicon containing material is such that the iron alloy formed therewith contains a minimum of 30 per cent silicon.

The present invention is based upon the discovery that silicon is an effective reducing agent for the recovery of tin from tin containing materials, such as ores, concentrates, slag, etc., under certain conditions. The invention is applicable for the recovery of tin from materials containing not more than about 20 per cent of tin and which are essentially oxygen compounds of tin, iron, silicon, aluminum, calcium and magnesium and in which the ratio of the combined amounts by weight of lime, alumina, magnesia and iron oxide to silica is substantially greater than one and the ratio of iron to tin is not less than about 1.5 to 1. When such a material is melted in a suitable furnace at a temperature between about 1,300 to 1,500 C. with an amount of silicon at least as great as the amount theoretically required to reduce all the iron oxide, computed as ferrous oxide, to metal, an alloy containing substantially equal amounts of tin and iron is obtained together with a slag containing not substantially more than 0.1 per cent tin. The amount of silicon used, preferably, should not be substantially more than that theo retically required to reduce to metal the combined amounts of iron oxide and tin oxide computed as ferrous oxide and stannic oxide. Most satisfactory results have been obtained when the composition of the furnace charge ice is such that the ratio of the combined weights of the basic components, such as lime, alumina and magnesia, to the weight of acidic components, such as silica, in the slag produced is substantially greater than one. To assure these results the composition of the charge may be adjusted by adding a basic material, such as lime, when necessary.

The iron-tin alloy thus produced then may bemelted with ferrosilicon and poured into a suitable mold. When the ferrosilicon contains about per cent silicon, the amount used may be between 50 to per cent of the weight of the alloy treated. Nearly all the tin is found at the bottom of the cold casting as 97-98 per cent tin, while the upper portion consists of brittle ferrosilicon which can be crushed and used for further precipitation.

While the present invention contemplates the' use of silicon as the reducing agent in its first stage, that is, in the recovery of the tin-iron alloy from ore concentrates, slag, etc., it is more practical to employ an alloy of silicon as the reducing agent, such as ferrosilicon. Similar results can be obtained when other known reducing agents for iron oxide are used in conjunction with silicon or ferrosilicon, such as aluminum, calcium, magnesium, etc. For example, other alloys such as calcium carbide or calcium silicide may be mixed with ferrosilicon. The

effective reducing agent, however, should be predominate-' Texas City was treated and had approximately the following composition:

Percent SiOz 41.5 FeO 15.6 Al203 18.5 0210 20.5 MgO 0.58 Sulfur 0.16 Tin 0.95

100 pounds of this finely divided slag was mixed with 5 pounds of a finely divided alloy containing 66.5 per cent silicon, 8 per cent aluminum and 25 per cent iron and the mixture was melted in an electric furnace at a temperature between 1,300 and 1,500" C. The heating was continued for 1 /2 hours to assure completion of the reaction and the reaction mass was poured into a mold to cool. A button of metal weighing 2.1 pounds was recovered from the bottom of the casting which was composed of iron and tin except for incidental impurities. The slag produced contained 0.12 percent tin. The recovery of tin in the iron-tin alloy metal button was 89.1 percent.

Example 2 In this example a low grade Bolivian tin concentrate was treated and had approximately the following composition:

100 pounds'of this concentrate, crushed to minus 100 mesh, wasmixed with 9'pounds of the same finely divided alloy used in Example 1 and the mixture was melted in an electric furnace at a temperature of 1,300 to 1,500 C. The heating was Continued for l /zhours to assure completion of the reaction and the reaction mass was poured into a mold to cool. A button of metal weighing 25.2 pounds was recovered from the bottom of the casting which was composed of iron and tin exceptfor incidental impurities. Theslag produced contained 0.1 percent tin. The recovery of tin in the iron-tin alloy metal button was 99.3 percent.

While I'do not wish to limit the invention and the appended claims to any'theory, I believe that the reaction may take place as follows. The molten mass of ore or concentrates contains a'piuralityof atoms, such as atoms of oxygen, tin, iron, aluminum, etc. Some of these atoms have positively charged electrons while others have negatively charged electrons and form an electrically neutral mass or pattern. When silicon is introduced into the molten mass, its positively charged electrons upset the neutrality of the electrically neutral pattern and replace some of the positively charged electrons previously preseiit, such'as tho'se'carried by the tin atoms, and as a result atoms of tin are precipitated.

I claim: I

l. The method for obtaining a high recovery of tin from materials containing not more than about 20 per cent of tin and which are essentially oxygen compounds of tin, iron, silicon, aluminum, calcium and magnesium and in which the ratio of the combined amount by weight of lime, alumina, magnesia and iron oxide to silica is greater than one and not greater than about 5 and the ratio'of iron to tin is not less than about 1.5 and not greater than about 12 which comprises melting a finely divided mixture comprising essentially said material and a reducing agent which comprises essentially silicon, recovering from the reaction mass the major portion of the tin in said material as an alloy containing substantially equal amounts by weight of tin and iron, and controlling the composition of said mixture to produce a slag in which the ratio of the weights of basic components to acidic components is greater than one, the amount of reducing agent used being at least equal to the amount theoretically required to reduceto metal all the iron oxide in said material and being not more than about the amount theoretically required to reduce to metal the combined amounts of iron oxide and tin oxide in said material when the iron oxide and tin oxide are computed as ferrous oxide and stannic oxide.

.2. The method as described by claim 1 in which the reducing agent includes ferros'ilicon.

3. The method as described by claim 1 in which the reducing agent includes an alloy of aluminum, silicon, and iron.

References Cited in the file of this patent UNITED sTATEs PATENTS Lamy Dec. 9, 1924 Lamyet'al. Oct. 6, 1931

Claims (1)

1. THE METHOD FOR OBTAINING A HIGH RECOVERY OF TIN FROM MATERIALS CONTAINING NOT MORE THAN ABOUT 20 PER CENT OF TIN AND WHICH ARE ESSENTIALLY OXYGEN COMPOUNDS OF TIN, IRON, SILICON, ALUMINUM, CALCIUM AND MAGNESIUM AND IN WHICH THE RATIO OF THE COMBINED AMOUNT BY WEIGHT OF LIME, ALUMINA, MAGNESIA AND IRON OXIDE TO SILICA IS GREATER THAN ONE AND NOT GREATER THAN ABOUT 5 AND THE RATIO OF IRON TO TIN IS NOT LESS THAN ABOUT 1.5 AND NOT GREATER THAN ABOUT 12 WHICH COMPRISES MELTING A FINELY DIVIDED MIXTURE COMPRISING ESSENTIALLY SAID MATERIAL AND A REDUCING AGENT WHICH COMPRISES ESSENTIALLY SILICON, RECOVERING FROM THE REACTION MASS THE MAJOR PORTION OF THE TIN IN SAID MATERIAL AS AN ALLOY CONTAINING SUBSTANTIALLY EQUAL AMOUNTS BY WEIGHT OF TIN AND IRON, AND CONTROLLING THE COMPOSITION OF SAID MIXTURE TO PRODUCE A SLAG IN WHICH THE RATIO OF THE WEIGHTS OF BASIC COMPONENTS TO ACIDIC COMPONENTS IS GREATER THAN ONE, THE AMOUNT OF REDUCING AGENT USED BEING AT LEAST EQUAL TO THE AMOUNT THEORETICALLY REQUIRED TO REDUCE TO METAL ALL THE IRON OXIDE IN SAID MATERIAL AND BEING NOT MORE THAN ABOUT THE AMOUNT THEORETICALLY REQUIRED TO REDUCE TO METAL THE COMBINED AMOUNTS OF IRON OXIDE AND TIN OXIDE IN SAID MATERIAL WHEN THE IRON OXIDE TIN OXIDE ARE COMPUTED AS FERROUS OXIDE AND STANNIC OXIDE.