Leaching Process

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What is the Leaching Process?

The process of leaching is used to extract the substances from the solids. This process is carried out when the given substance is allowed to dissolve in a liquid. It is carried out either through a natural process or industrially.

The leaching process shows the release of both the organic as well as the inorganic radionuclides or contaminants from a solid-state to a liquid state when they get influenced by different processes like mineral dissolution, complexation, and desorption.

The process of leaching is known to be a universal process in which water tends to leach the material components that come in contact with it. This can be its surface or its interior depending on how porous the material is.

The ore of the given metal can be concentrated using this process when a chemical reaction is caused with the help of a reagent that would eventually lead to the ore getting dissolved and the impurities undissolved. 

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Leaching Process Examples

The leaching process example includes the leaching of bauxite or Al₂O₃ . 2H₂O with the concentrated and heated sodium hydroxide. The concentrated NaOH here tends to dissolve the aluminium present in the given bauxite, while on the other hand, the impurities like SiO₂, TiO₂, and Fe₂O₃ do not get dissolved. The chemical reaction of this leaching process is given as follows.

Al₂O₃ . 2H₂O + 2NaOH → 2NaAlO₂ = 3H₂O

Another example of the process of leaching is leaching of the noble metals like silver and gold in the presence of the dilute aqueous solutions of either potassium cyanide or sodium cyanide in the presence of air.  The chemical reaction for this process of leaching for silver is given below.

Ag₂S + 4 NaCN → 2Na[Ag(CN)₂] + Na₂S

The leaching process also causes the loss of nutrients that are present in the soil because of heavy rainfalls. 

Advantages and Disadvantages of Leaching Process

Advantages of Leaching are as Follows.

  1. The leaching process is easier when it comes for the execution.

  2. It is not a harmful process in comparison to the other pyrometallurgical methods.

  3. It does not lead to any sorts of gaseous pollutants.

Disadvantages of Leaching are as Follows.

  1. The residual liquid waste that is generated from the leaching process is highly acidic in nature.

  2. The effluent of the leaching process is toxic.

  3. The efficiency of the leaching process is entirely dependent on temperature.

Types of Leaching Processes in Metallurgy

The different kinds of leaching processes which are used in industrial purposes for metallurgy are given below.

  1. Heap leaching: It refers to a process which extracts uranium, copper and many other precious metals from their ores.

  2. In-situ leaching: It is a process which recovers uranium and copper.

  3. Tank leaching and vat leaching: They are the processes in which the ores are to be placed in vats or large tanks that consist of the leaching solutions. These processes are used for the extraction of the metals from their ores.

FAQ (Frequently Asked Questions)

1. What is Heap Leaching?

Ans: The heap leaching is a kind of industrial mining process which is useful for the extraction of precious metals, uranium, copper and several other compounds from their respective ores. This is done with the help of a series of chemical reactions that tend to absorb specific minerals and tend to re-separate them once they undergo a division from several other earth materials. 

The process of heap leach mining occurs when the ore is placed on a liner and the chemicals are then added to it with the help of the drip system. This process is extensively used in today’s larger-scale operations of mining since it generates the desired concentrates at a comparatively lower cost when compared to the traditional methods of processing like vat leaching, agitation, and flotation.

2. What is Vat Leaching?

Ans: Vat leaching is a process which is carried out in the vats that have a capacity ranging from 30 - 1200 tons. The sand used for leaching gets separated from the slime in the cones, classifiers, V boxes and the collecting vats that are filled by the distributors. The overflow in each of the mentioned cases is either the finer portion of the ore or the slime. 

Leaching is the process which involves the mixed and neutralized sand vat, water washes, enough contact with the weak and the strong cyanide solutions, the rapid filling and discharging, and the aeration of the solution and the sand.

This process is very effective and cheap to clean the ores wherein the process of fine grinding is not required for a better extraction.

3. What is In Situ Leaching?

Ans: The in-situ leaching is a leaching method in which the metal values are directly leached from their ores without the need to excavate the ore before leaching. The leaching reagents which tend to dissolve the metals that are desired get pumped to the deposit via the injection wells. The leachate gets collected in the centrally located underground wells or dumps and then later gets pumped to the surface via the recovery wells to undergo the further processing above the ground. The permeability of the body of the ore is essential and in case the ore does not have the natural porosity that is required, it gets fractured by the explosives. This allows the injected solution from through the deposit.

The ores that are suitable for the in-situ leaching are generally situated below the aquifer. This method is used for the extraction of the uranium, copper and several other soluble salts like potash, halite, boron and the magnesium minerals.