Salt extraction process

Last updated

The salt extraction process is an electrolytic method which may be used to extract valuable metals from slag, low-grade ores, or other materials by using molten salts. This method was developed by S. Seetharaman, O. Grinder, L. Teng and X. Ge at the Royal Institute of Technology in Sweden as part of a large Steel Eco-Cycle Project in 2005.

Slag glass-like by-product left over after a desired metal has been separated from its raw ore

Slag is the glass-like by-product left over after a desired metal has been separated from its raw ore. Slag is usually a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and elemental metals. While slags are generally used to remove waste in metal smelting, they can also serve other purposes, such as assisting in the temperature control of the smelting, and minimizing any re-oxidation of the final liquid metal product before the molten metal is removed from the furnace and used to make solid metal.

Sweden constitutional monarchy in Northern Europe

Sweden, officially the Kingdom of Sweden, is a Scandinavian Nordic country in Northern Europe. It borders Norway to the west and north and Finland to the east, and is connected to Denmark in the southwest by a bridge-tunnel across the Öresund, a strait at the Swedish-Danish border. At 450,295 square kilometres (173,860 sq mi), Sweden is the largest country in Northern Europe, the third-largest country in the European Union and the fifth largest country in Europe by area. Sweden has a total population of 10.2 million of which 2.4 million has a foreign background. It has a low population density of 22 inhabitants per square kilometre (57/sq mi). The highest concentration is in the southern half of the country.

Contents

Description

In the first step of this process, the slag or other raw materials containing metal values of interest, e.g. chromium, is dissolved into the molten salt phase at a suitable temperature. A suitable flux must be found in order to achieve the dissolution of oxides. According to the Fajans' rules, AlCl3, as a covalent metal chloride, is able to release chloride ions, which then can effectively break the chemical bonds between metal and oxygen atoms, leading to the formation of corresponding soluble metal chlorides and capture of oxygen in Al2O3. AlCl3 was proved indeed to be a powerful fluxing agent in this regard. [1]

Fajans rules

In inorganic chemistry, Fajans' rules, formulated by Kazimierz Fajans in 1923, are used to predict whether a chemical bond will be covalent or ionic, and depend on the charge on the cation and the relative sizes of the cation and anion. They can be summarized in the following table:

In the second step, the salt phase is subjected to electrolysis in order to recover the metal of interest as a cathode deposit. The salt melt used for extraction can be recycled. The metals can be selectively electrodeposited from the salt melt. There is also the option of aqueous processing of the salt phase containing the metal values. The process can design to be continuous by combining the two steps. The anode off-gas from electrolysis, Cl2 can be reused for accentuating the dissolution of the raw materials. On the other hand, the residue after processing, which consists essentially of Al2O3, can safely be used for landfill, building construction or as a raw material for the refractory industry.

Application

This process had been successfully employed for the recovery of chromium and iron from the electric furnace slag generated from the stainless steelmaking process, or from low-grade chromite ore. [2] It is also extended to extract copper or iron from both copper oxides and sulfides. [3]

Chromium Chemical element with atomic number 24

Chromium is a chemical element with symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard and brittle transition metal. Chromium boasts a high usage rate as a metal that is able to be highly polished while resisting tarnishing. Chromium is also the main additive in stainless steel, a popular steel alloy due to its uncommonly high specular reflection. Simple polished chromium reflects almost 70% of the visible spectrum, with almost 90% of infrared light waves being reflected. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored.

Iron Chemical element with atomic number 26

Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space.

Stainless steel steel alloy resistant to corrosion

In metallurgy, stainless steel, also known as inox steel or inox from French inoxydable (inoxidizable), is a steel alloy, with highest percentage contents of iron, chromium, and nickel, with a minimum of 10.5% chromium content by mass and a maximum of 1.2% carbon by mass.

The electrochemical behaviors of the metal ions (Cr, Cu, Fe, Mg, Mn) in the molten salts (NaCl-KCl-(CaCl2))with respect to this process were also extensively investigated. [4] Those results are also useful for the industrial electrowinning processes of related metal or alloy production.

Electrowinning

Electrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution via a process commonly referred to as leaching. Electrorefining uses a similar process to remove impurities from a metal. Both processes use electroplating on a large scale and are important techniques for the economical and straightforward purification of non-ferrous metals. The resulting metals are said to be electrowon.

Related Research Articles

Electrochemistry branch of chemistry

Electrochemistry is the branch of physical chemistry that studies the relationship between electricity, as a measurable and quantitative phenomenon, and identifiable chemical change, with either electricity considered an outcome of a particular chemical change or vice versa. These reactions involve electric charges moving between electrodes and an electrolyte. Thus electrochemistry deals with the interaction between electrical energy and chemical change.

Ore rock with valuable metals, minerals and elements

An ore is an occurrence of rock or sediment that contains sufficient minerals with economically important elements, typically metals, that can be economically extracted from the deposit. The ores are extracted from the earth through mining; they are then refined to extract the valuable element, or elements.

Electrolysis technique that uses a direct electric current to drive an otherwise non-spontaneous chemical reaction

In chemistry and manufacturing, electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential.

Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science, covering all aspects of the types of ore, washing, concentration, separation, chemical processes and extraction of pure metal and their alloying to suit various applications, sometimes for direct use as a finished product, but more often in a form that requires further working to achieve the given properties to suit the applications.

Potassium chloride chemical compound

Potassium chloride (KCl) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water and its solutions have a salt-like taste. KCl is used as a fertilizer, in medicine, in scientific applications, and in food processing, where it may be known as E number additive E508.

Electrolytic cell

An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy. They are often used to decompose chemical compounds, in a process called electrolysis—the Greek word lysis means to break up.

Iron(III) chloride chemical compound

Iron(III) chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3 and with iron in the +3 oxidation state. The colour of iron(III) chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red. Anhydrous iron(III) chloride is deliquescent, forming hydrated hydrogen chloride mists in moist air. It is rarely observed in its natural form, the mineral molysite, known mainly from some fumaroles.

In chemistry, a reactivity series (or activity series) is an empirical, calculated, and structurally analytical progression of a series of metals, arranged by their "reactivity" from highest to lowest. It is used to summarize information about the reactions of metals with acids and water, double displacement reactions and the extraction of metals from their ores.

Copper extraction

Copper extraction refers to the methods used to obtaining copper from its ores. The conversion of copper consists of a series of chemical, physical, and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.

Chloralkali process

The electrolysis of brine is an industrial process for the electrolysis of sodium chloride. It is the technology used to produce chlorine and sodium hydroxide, which are commodity chemicals required by industry. 35 million tons of chlorine were prepared by this process in 1987. Industrial scale production began in 1892.

Copper(II) chloride chemical compound

Copper(II) chloride is the chemical compound with the chemical formula CuCl2. This is a light brown solid, which slowly absorbs moisture to form a blue-green dihydrate. The copper(II) chlorides are some of the most common copper(II) compounds, after copper sulfate.

The Kroll process is a pyrometallurgical industrial process used to produce metallic titanium. It was invented in 1940 by William J. Kroll in Luxembourg. After moving to the United States, Kroll further developed the method for the production of zirconium. The Kroll process replaced the Hunter process for almost all commercial production.

Hydrometallurgy is a method for obtaining metals from their ores. It is a technique within the field of extractive metallurgy involving the use of aqueous chemistry for the recovery of metals from ores, concentrates, and recycled or residual materials. Metal chemical processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:

The FFC Cambridge Process is an electrochemical method in which solid metal compounds, particularly oxides, are cathodically reduced to the respective metals or alloys in molten salts. It is thought that this process will eventually be capable of producing metals or alloys more efficiently than by current conventional processes, such as titanium by the Kroll process.

Tin(II) chloride chemical compound

Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula SnCl2. It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent (in acid solution), and in electrolytic baths for tin-plating. Tin(II) chloride should not be confused with the other chloride of tin; tin(IV) chloride or stannic chloride (SnCl4).

Metal ammine complex class of chemical compounds

In coordination chemistry, metal ammine complexes are metal complexes containing at least one ammonia (NH3) ligand. "Ammine" is spelled this way due to historical reasons; in contrast, alkyl or aryl bearing ligands are spelt with a single "m". Almost all metal ions bind ammonia as a ligand, but the most prevalent examples of ammine complexes are for Cr(III), Co(III), Ni(II), Cu(II) as well as several platinum group metals.

The Downs' process is an electrochemical method for the commercial preparation of metallic sodium, in which molten NaCl is electrolyzed in a special apparatus called the Downs cell. The Downs cell was invented in 1922 by the American chemist James Cloyd Downs (1885–1957).

Bronze disease is the irreversible and nearly inexorable corrosion process occurring when chlorides come into contact with bronze or other copper-bearing alloys. It occurs as a dark green or a lighter fuzzy green coating on copper, bronze, and other copper-bearing alloys generally due either to contamination by salt water or after burial in dirt. If not treated, complete destruction of the affected artifact is possible. Transfer of chlorides from the contaminated artifact to other artifacts can spread the condition.

Non-ferrous extractive metallurgy

Non-ferrous extractive metallurgy is one of the two branches of extractive metallurgy which pertains to the processes of reducing valuable, non-iron metals from ores or raw material. Metals like zinc, copper, lead, aluminium as well as rare and noble metals are of particular interest in this field, while the more common metal, iron, is considered a major impurity. Like ferrous extraction, non-ferrous extraction primarily focuses on the economic optimization of extraction processes in separating qualitatively and quantitatively marketable metals from its impurities (gangue).

References

  1. ↑ Salt Extraction AB. A process for chlorinating resources containing recoverable metals. International Publication Date (19.11.2009). International Application Number: PCT/SE2009/050538. International Publication Number: PCT: WO 2009/139 715 A1 (World Patent)
  2. ↑ X. Ge, O. Grinder, S. Seetharaman. The salt extraction process-A novel route for metal extraction Part I: Cr, Fe recovery from EAF slags and low-grade chromite ores. Trans. IMM,C, 119(2010), 27-32.
  3. ↑ X. Ge, S. Seetharaman. The salt extraction process-A novel route for metal extraction Part II: Cu/Fe extraction from copper oxides and sulfides. Trans. IMM,C, 119(2010),93-100.
  4. ↑ X. Ge, S. J. Xiao, G. M. Haarberg, S. Seetharaman. The salt extraction process-A novel route for metal extraction Part III: Electrochemical behaviors of the metal ions(Cr, Cu, Fe, Mg, Mn) in molten (CaCl2-)NaCl-KCl salt system. Trans. IMM, C, 119(2010), 163-170.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.