Why Is Ore Concentration Important in Chemistry?
Metals are tremendously important to a high-energy society. They transport electricity in the electrical grid, they are essential components in the automobile and digital industry and so on. Except for gold, all other metals are seen as compound forms in the earth's crust. The naturally occurring chemical compounds which are the source of one or more than one metal are called minerals which are obtained during mining.
Among these minerals, very few are actually suitable for the isolation and extraction of metals for commercial processes called ores. The entire process of isolation and extraction of metals from its ore is known as metallurgy. The first step in isolating metal is the concentration of metal from the corresponding ore. The ore in the earth's crust contains so many unwanted substances clay, sand also some other chemical compounds. The removal of unwanted substances or impurities from metal ore is called the concentration of ore.
Concentration of Iron Ore
The most used ores of iron for the extraction of iron metal are hematite and magnetite. These are rich sources of iron and they are known as natural ore or direct shipping ore meaning they can be directly used in blast furnaces. The concentration method of iron ore is magnetic separation. The powdered magnetite or hematite is subjected to a conveyer belt and when the magnetic roller starts rotating, the iron particles get attracted towards the roller and all other impurities are separated away from it. In the ore iron, the mineral pyrite is found associated with it. It is non-magnetic and can be removed through magnetic separation.
Methods of Concentration of Ore
Hydraulic Washing
This method is suitable if the gangue in metal is lighter than metal. Or more precisely, we can say that this method is based on the difference in specific gravity of metal and gangue. In this method, the metal ore is subjected to a stream of running water so that the lighter gangue particles will be washed away and heavier ore particles will be left behind. It is, therefore, a type of gravity separation.
Magnetic Separation
This method is based on the difference in magnetic properties of ore and gangue. Either the ore or the gangue should be magnetic. In this process, the powdered ore is subjected to a conveyer belt and moves over a magnetic roller. By this time, the magnetic particles remain attracted towards the belt and fall close to it and non-magnetic materials are separated away from it.
Ores of iron and copper can be separated using magnetic separation. In the ore of iron like hematite (Fe2O2), magnetite (Fe3O4) and siderite(FeCO3), the ore is magnetic and gangue is non-magnetic; hence, the ore particle remains close to the magnetic roller and impurities are separated away. For copper ore, copper pyrites (CuFeS2) contain iron as impurity is attracted towards the magnetic roller and the ore is separated away.
Froth Flotation
This method is used to separate gangue from sulphide ores. The ore particle is suspended in water. Along with this collectors (pine oil, fatty acids, xanthate etc.) and stabilisers (cresol, aniline etc) are added. The collectors enhance the non-wettability of mineral particles whereas stabilisers stabilise the form. The mineral particles are wet by oil and the gangue particles are wet by water. A rotating paddle agitates the mixture and draws air into it. As a result, light froth is formed and the mineral particles are carried in it. The froth is later dried and then the mineral particles are recovered.
Leaching
Leaching is suitable if the ore is soluble in some chemical solvent and the impurities are insoluble in it. The ore particle is converted to soluble salt of the solvent and the undissolved impurities can be washed off. The materials left over are commonly known as tailing.
Use of Leaching During Concentration of Ore
Leaching is one of the processes for the concentration of ore. Here, the ore is treated with some chemicals and made into a soluble salt. But impurities are not soluble in the chemical and it remains as such. After the processing, metal can be extracted from the solution.
In comparison, pyrometallurgy leaching is very economical and energy efficient. It does not require extreme conditions of pressure and temperature. Also, a high amount of metals can be extracted through leaching compared to the traditional concentration methods.
Key Features
The concentration of ore is the removal of impurities from metal ore.
In iron ore, the non-magnetic impurities from magnetic iron ore are separated by the magnetic separation process.
Leaching is a process which involves the use of chemical substances to dissolve metal ore which has significant use in the concentration process as it is easy to perform and pollution free.
Conclusion
The concentration of ore is the first step in the isolation of metals. It is the removal of impurities from metal ore. Based on the physical nature of metal ore, different concentration methods are there like hydraulic washing, leaching, froth flotation and magnetic separation. One of the most common examples is the separation of Iron ores which are concentrated using magnetic separation.
FAQs on Concentration of Ore: Key Methods and Concepts
1. What does 'concentration of ore' mean in chemistry?
Concentration of ore, also known as ore dressing or benefaction, is the process of removing unwanted earthly or rocky impurities, called gangue, from the ore. This increases the percentage of the metal compound in the ore, making the subsequent extraction process more efficient and cost-effective.
2. Why is it necessary to concentrate an ore before extracting the metal?
It is essential to concentrate an ore to remove the non-metallic impurities (gangue). If these impurities are not removed, they can interfere with the extraction process, consume extra energy, and reduce the purity and yield of the final metal. Concentrating the ore first makes the entire metallurgical operation more economical and efficient.
3. What are the main methods for the concentration of ores?
The choice of method depends on the properties of the ore and the gangue. The four principal methods are:
- Hydraulic Washing: Used when the ore particles are denser than the gangue.
- Magnetic Separation: Used when either the ore or the gangue is magnetic.
- Froth Flotation: Primarily used for concentrating sulphide ores.
- Leaching: A chemical method used when the ore is soluble in a specific solvent.
4. How do you decide which method to use for concentrating a particular ore?
The decision is based on the differences in the physical and chemical properties between the ore mineral and the gangue. For example, if an ore like hematite (iron ore) is magnetic but the impurities are not, magnetic separation is used. If there is a large density difference, like in tin ore, hydraulic washing is effective. For sulphide ores like zinc blende, which are preferentially wetted by oil, froth flotation is the ideal choice.
5. Can you explain how the froth flotation method works with an example?
The froth flotation method is based on the principle of differential wetting. In a mixture of water and pine oil, sulphide ore particles are preferentially wetted by oil, while gangue particles are wetted by water. When air is bubbled through the mixture, the oil-coated ore particles rise to the surface as a froth, which can be skimmed off. This is a common method for concentrating zinc blende (ZnS) and copper pyrites (CuFeS₂).
6. What is leaching and for which types of ores is it typically used?
Leaching is a chemical concentration method where the powdered ore is treated with a reagent that selectively dissolves the valuable metal compound, leaving the impurities behind. It is used when the ore is soluble and the gangue is not. A key example is the leaching of bauxite ore (Al₂O₃) with a concentrated NaOH solution in the Baeyer's process to extract alumina. It is also used for the extraction of precious metals like gold and silver.
7. What is the difference between a mineral and an ore?
The key difference lies in profitability. A mineral is a naturally occurring chemical substance. An ore is a specific type of mineral from which a metal can be extracted economically and conveniently. In simple terms, all ores are minerals, but not all minerals are valuable enough to be considered ores.
8. Does concentrating an ore change its chemical composition?
Generally, no. Most concentration methods, like hydraulic washing and magnetic separation, are physical processes that simply separate the ore from the gangue without altering the chemical formula of the metallic compound. The main exception is leaching, which is a chemical process that dissolves the ore to separate it, but the goal is to recover the original compound in a purer form later.
