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What is meant by Concentration of Ores?

  • Last Updated : 07 Feb, 2022

Metals are found in ore in complexes with other elements. The process of removing metal from its ore is known as metal extraction. The methods of extracting metals from their ores and refining them are referred to as metallurgy. All of the metals cannot be extracted using a single process. Depending on the metal, the processes to be used varies. One of the most critical phases in the extraction of metal from its ore is ore concentration, also known as ore enrichment.

What is Ore?

Ore is defined as a solid substance (such as a rock) that includes minerals or a combination of minerals, from which metal can be recovered by a series of procedures such as ore concentration, metal isolation, and metal refining. Ores are broadly categorized into four types:

  1. Native ore: These are the non-reactive ores that include metal in their free state. Examples include silver, gold, and platinum.
  2. Oxidized ore: These contain oxides or oxy-salts, which are metal carbonates, phosphates, and silicates. Oxide ores (Fe2O3) and carbonate ores are two examples (CaCO3).
  3. Sulphurized ore: These contain metal sulphides such as iron and lead. Examples include FeS2 (Iron pyrites), PbS (Galena), and HgS (Cinnabar).
  4. Halide ore: Metal halide is present in these. Chloride ore: AgCl (Horn silver), CaF2 (Fluorspar), and so forth.

What is Concentration?

Concentrating ore is a method of removing gangue particles and other impurities. Alternative names for ore concentration include ore-dressing and benefaction. The procedure of ore concentration is a critical stage in obtaining pure metal from ore. Separating ore from gangue particles is required for metal extraction. 

Ore discovered in the soil contains several impurities such as sand, grit, pebbles, and so on, which are collectively referred to as “Gangue.” The initial step in metal extraction is ore concentration. There are several forms of ore, such as native, oxidised, sulphurized, and halide, that can be concentrated using various physical and chemical processes.

Methods of the Concentration of Ore

Because the ore is located on the earth’s surface, it contains undesired earthy components such as boulders, sand, silt, and a variety of other impurities known colloquially as gangue. Concentration is the separation of something helpful from something worthless. Thus, we can recover and refine metals by concentrating ore from such contaminants. To concentrate or extract ore from the gangue matrix, various physical and chemical procedures are used.

Physical methods for ore concentration

Physical methods for ore concentration include handpicking, hydraulic washing, magnetic separation, and froth flotation.

Hand-picking

It was the traditional way of directly concentrating ore with one’s hands. In this technique, a hammer is used to remove the gangue, or adherent solid matrix, from the ore. Gangue separation and identification are based on distinctions in colour or lump shape.

Hydraulic Washing

It’s also known as “Gravity separation” or “Levigation.” This process concentrates the ore by passing it through an upward stream of water, separating the lighter gangue particles from the heavier metal ore. This is a type of gravity separation.

Magnetic Separation

This includes separating the ore and gangue using magnetic characteristics of either the ore or the gangue. The ore is first crushed into fine particles before being transported on a conveyor belt that passes past a magnetic roller. The magnetic ore remain

the belt, while the gangue falls off.

Froth Flotation Method

This technique is mostly used to extract gangue from sulphide ores. The ore is pulverised, and a suspension in water is formed. This is supplemented with collectors and froth stabilisers. Collectors (pine oils, fatty acids, etc.) increase the ore’s metal component’s non-wettability and allow it to form a froth. Cresols, aniline, and other froth stabilisers maintain the foam in place. The metal is lubricated by the oil, while the gangue is lubricated by the water. The froth is created by constantly stirring the suspension with paddles and air. The frothy metal is skimmed off the top and dried to recover the metal. The following are the stages of flotation:

  1. The initial stage of flotation is roughing. The largest amount of useful material is extracted during this operation. Before roughing, a pre-flotation procedure is sometimes used. This is done to get rid of contaminants like organic carbon.
  2. Cleaning is the next step in the flotation process. Unwanted content is deleted during this process. This step’s output is known as cleaner concentrate.
  3. The final phase in the flotation process is scavenging. This is done to recover critical materials that were not collected during roughing.

Chemicals of flotation process

  1. Anionic Sulphur ligands serve as collectors. For instance, xanthate salts. Fatty acids and fatty amines are also utilised as collectors.
  2. Frothers are employed to keep the froth stable. For example, pine oil, alcohols, and so on.
  3. To optimise the separation process, modifiers are utilised. Lime (CaO), Caustic soda (NaOH), and other pH adjusters are available. Phosphates, silicates, and carbonates are examples of anionic modifiers. Organic modifiers include thickeners such as dextrin, starch, glue, and others.

Leaching

When the ore is soluble in a solvent, leaching is performed. The powdered ore is dissolved in a chemical, often a strong NaOH solution. The metal in the ore is dissolved by the chemical solution, and it can be recovered and separated from the gangue by extracting the chemical solution. This method is used to extract aluminium metal from bauxite ore.

Chemical methods for ore concentration

For more concentration, chemical processes such as calcination, roasting, and leaching are used.

Calcination

Calcination is the process of transforming ore into oxide by rapidly heating it. In the absence of air or in restricted availability, the ore is heated below its melting point. This process is frequently used to convert carbonates and hydroxides to their corresponding oxides. Moisture and volatile contaminants are also eliminated during calcination. Calcination is a thermal process that is used to convert ores and other solid materials by breaking them down through heat. The reaction in calcination occurs most of the time at or above the thermal breakdown temperature. As a result, calcination is mostly used in the conversion of limestone (calcium carbonate) to lime (calcium oxide) and carbon dioxide.

CaCO3 ⇢ CaO + CO2

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Roasting

It is a metallurgical process in which ore is transformed into oxide by heating it below its melting point in the presence of extra air. While calcination is usually employed for carbonate oxidation, roasting is a process for transforming sulphide ores. Moisture and non-metallic contaminants are emitted as volatile gases during roasting. Solid-gas thermal processes such as oxidation, reduction, sulfation, chlorination, and pyro hydrolysis make up the roasting process. However, sulphide-based roasting is a major source of air pollution, and the main disadvantage of this method is that it emits a large amount of metallic, poisonous, and acidic substances that affect the environment.

2ZnS + 3O2 ⇢ 2ZnO + 2SO2

Leaching

It is a chemical process in which the ore is treated with the appropriate reagent to dissolve it. Separating the soluble ore or mineral from the insoluble gangue is possible. Following ore separation, it can be recovered using a variety of chemical techniques.

Sample Questions

Question 1: What is handpicking?

Answer:

It was the old way of directly concentrating ore with the hands. With the use of a hammer, the gangue or adhering solid matrix is removed from the ore in this procedure. The separation and identification of gangue is based on colour or lump form differences.

Question 2: What is leaching?

Answer:

It is a chemical process in which the ore is treated with the appropriate reagent to make it soluble. Separating the soluble ore or mineral from the insoluble gangue is possible. Several chemical processes can be used

ecover ore once it has been separated.

Question 3: What are the three stages of flotation?

Answer:

  1. Roughing is the initial step in the flotation process. The largest amount of useful material is extracted during this operation. Before roughing, the pre-flotation phase is sometimes used. This is done to get rid of contaminants like organic carbon.
  2. The next phase in flotation is cleaning. Unwanted content is deleted during this process. Cleaner concentration is the end result of this stage.
  3. The final phase in the flotation process is scavenging. This is done to recover essential materials that were not recovered during the roughing process.Scavenging is the last step of the flotation process. This is done to recover essential materials that were not recovered during the roughing process.

Question 4: What is an ore?

Answer:

Ore is a solid substance (like a rock) that includes minerals or a combination of minerals from which metal can be recovered using a variety of procedures such as ore concentration, metal isolation, and metal refining.

Question 5: What is magnetic separation?

Answer:

Magnetic properties of either the ore or the gangue are utilised to separate the ore and gangue. The ore is first finely processed before being conveyed on a conveyor belt that passes past a magnetic roller. The magnetic ore stays on the belt, while the gangue slides off.


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