Mineral Concentrates

DESCRIPTION

Its symbol is Bi, it is a scarce metallic chemical element, pinkish in color. Its atomic number Z is 83 and it is in group 15 of the periodic system. It occupies the 73rd place in abundance among the elements of the earth’s crust, it represents 8.5×10^-7 % of the weight of the crust and is as scarce as silver. The main deposits are in South America, it is normally obtained as a by-product of the refining of Copper and Lead concentrates.

PROPERTIES

Bismuth is a grayish-white, crystalline, lustrous, hard and brittle metal. It is one of the few metals that expand when solidified. Its thermal conductivity is lower than that of any other metal except mercury. Bismuth is inert in dry air at room temperature, but oxidizes slightly when wet. It rapidly forms an oxide film at temperatures above its melting point, and ignites on reaching red forming the yellow oxide, Bi₂O₃. The metal combines directly with halogens and with sulfur, selenium and tellurium, but not with nitrogen or phosphorus.

In almost all bismuth compounds it is in trivalent form. However, it can sometimes be pentavalent. Sodium bismuthate and bismuth pentafluoride are perhaps the most important Bi(V) compounds. The former is a powerful oxidizing agent and the latter a useful fluorinating agent for organic compounds.

Bismuth metal is neither classified as a hazardous substance by the EU nor as dangerous goods for transport.

APPLICATIONS

• Low melting point alloys.
• Lead substitute in copper alloys for water pipelines.
• Special welds.
• Bleaching effect in foundries.
• Pharmaceutical applications.

DESCRIPTION

Chromium is a chemical element with atomic number Z=24 and is found in group 6 of the periodic table of the elements. Its name “chromium” (derived from the Greek chroma, “color”) is due to the different colors of its compounds.

The usual method of obtaining chromium is as follows: first, the ore is heated together with the addition of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to its hexavalent form.

Subsequently, the chromate is transformed into oxide by reaction with sulfuric acid. Once the oxide is obtained, it is reduced to chromium metal by an aluminothermic process.

Elemental chromium is not found in nature. Its most important mineral due to its abundance is chromite.

PROPERTIES

Chromium is silvery white, hard and brittle. However, it is relatively soft and ductile when very pure. Its main uses are in the manufacture of corrosion-resistant alloys, such as stainless steel, which are very hard and heat-resistant, and as a coating for galvanizing.

Chromium metal is not classified as a hazardous substance by the EU and is not considered dangerous goods for transport.

APPLICATIONS

• Manufacture of stainless steels and other anti-corrosion alloys.
• Chrome plating coatings.
• Colorants.
• Catalysts.

DESCRIPTION

Tin (from Latin stannum) is a chemical element, with symbol Sn and atomic number Z=50. The most important tin ore is cassiterite, SnO₂. There are no known high-grade deposits of this mineral. Most of the world’s tin ore is obtained from low-grade alluvial deposits. There are two allotropic forms of tin: white tin and gray tin.

Tin is obtained from cassiterite, where it occurs as tin dioxide. This ore is ground and enriched in tin dioxide by flotation, then roasted and heated with coke in a reverberatory furnace to obtain the metal by carbothermal reduction.

PROPERTIES

It melts at low temperature; it has great fluidity when molten and has a high boiling point; it is also highly resistant to corrosion in many media. Tin reacts with both strong acids and strong bases, but is relatively resistant to near neutral solutions. Normally when subjected to a corrosion process, no hydrogen gas is released from the tin and the corrosion rate is governed by the supply of oxygen or other oxidizing agents; in its absence, corrosion is negligible. A thin oxide film forms on tin that is exposed to air and this gives rise to surface protection. Salts that react acidically in solution, such as aluminum chloride and ferric chloride, attack tin in the presence of oxidants or air. Most non-aqueous liquids, such as oils, alcohols or chlorinated hydrocarbons, have no significant effect on tin. Tin and simple inorganic salts are non-toxic, but some forms of organotin compounds are toxic.

Tin metal is not classified as a hazardous substance by the EU or as dangerous goods for transport.

APPLICATIONS

• Protective coatings against corrosion.
• Manufacture of bronzes.
• Soft soldering.
• Manufacture of ceramic enamels.

DESCRIPTION

Chemical element, atomic number Z=25. It is one of the transition metals of the first long period of the periodic table; it lies between chromium and iron. It has properties in common with both metals. Although little known or used in its pure form, it is of great practical importance in steelmaking. It is the twelfth most abundant element in the earth’s crust and is widely distributed.

It is found in hundreds of minerals, but only about a dozen are of industrial interest. They include: pyrolusite (MnO₂), psilomelane (MnO₂-H₂O), manganite (MnO(OH)), braunite (3Mn₂O₃-MnSiO₃), rhodonite (MnSiO₃), rhodochrosite (MnCO₃), hübnerite (MnWO₄), etc.

The countries with the largest deposits of manganese ores are South Africa, Ukraine, Bolivia and China. The metal is obtained by reduction of the oxides with aluminum, and ferromanganese is also obtained by carbothermal reduction of iron and manganese oxides.

PROPERTIES

Manganese is a fairly reactive metal. Although the solid metal reacts slowly, the metal powder reacts readily and, in some cases, very vigorously. When heated in the presence of air or oxygen, powdered manganese forms a red oxide, Mn₃O₄. With water at room temperature, hydrogen and manganese(II) hydroxide, Mn(OH)₂, are formed. In the case of acids, and because manganese is a reactive metal, hydrogen is released and a manganese(II) salt is formed. Manganese reacts at elevated temperatures with halogens, sulfur, nitrogen, carbon, silicon, phosphorus and boron.

Manganese oxidizes readily in air to form a brown layer of oxide. It also does so at elevated temperatures. In this respect its behavior is very similar to its higher atomic number neighbor iron.

Metallic manganese is neither classified as a hazardous substance in the EU nor as dangerous goods for transport.

APPLICATIONS

• Manufacture of steels.
• Stainless steels.
• Alloying agent in certain aluminum alloys.
• Manufacture of batteries as manganese dioxide.

DESCRIPTION

Wolfram, also called tungsten, is a chemical element with atomic number Z=74 and is found in group VI B of the periodic table of the elements. It is a rare metal in the earth’s crust, 57º in abundance, found as an oxide and as salts in certain minerals. The word wolfram comes from the German wolf and rahm, translated as “Wolf’s slime” in reference to the superstitions of medieval Saxon miners who believed that the devil appeared in the form of a wolf and inhabited the depths of the mines corroding the cassiterite. The word tungsten comes from Swedish; tung translates as “heavy” and sten, “stone”.

It is never found free in nature, but in the form of salts combined with other elements, mainly as scheelite (CaWO₄) and wolframite ((Fe,Mn)WO₄), which are its most important minerals. On the other hand we also have cuproscheelite (CuWO₄), ferberite (FeWO₄), Hübnerite (MnWO₄) and stolzite (PbWO₄). These ores are mined and used to produce about 35,000 tons of tungsten concentrates per year. China produces more than 75% of this total and most of the remaining production comes from: Austria, Bolivia, Portugal and Russia.

To extract the element from its ore, it is smelted with sodium carbonate to obtain sodium wolframate, Na2WO4. The soluble sodium wolframate is then extracted with hot water and treated with hydrochloric acid to obtain wolframic acid, H₂WO₄. The latter compound, once washed and dried, forms the oxide WO₃, which is reduced with hydrogen or carbon in an electric furnace. The fine powder obtained is reheated in molds in a hydrogen atmosphere and pressed into bars which are rolled and hammered at high temperature to make them compact and ductile. It is also possible to obtain it by hydrogen reduction of WF₆.

PROPERTIES

It is steel-gray in color, very hard and dense, has the highest melting point of all metals and the highest boiling point of all known elements. From the chemical point of view, tungsten is relatively inert. It is not easily attacked by common acids, alkalis or aqua regia. It reacts with a mixture of nitric and hydrofluoric acids. It is easily attacked by molten oxidizing salts, such as sodium nitrite. Gaseous chlorine, bromine, iodine, carbon dioxide, carbon monoxide and sulfur react with tungsten only at high temperatures. Carbon, boron, silicon and nitrogen also form compounds with it at elevated temperatures; with hydrogen it does not react.

Tungsten is not classified as a hazardous substance by the E.U. nor is it classified as dangerous goods for transport.

APPLICATIONS

• Manufacture of special steels.
• Manufacture of tungsten carbide for the manufacture of machining tools.
• TIG welding electrodes.
• Incandescent filaments and electrical resistors.
• Luminaires.