Leaching Process: Aluminium Hydroxide Precipitation

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SUMMARY

The leaching process of aluminium involves dissolving alumina from bauxite to form soluble sodium aluminate, followed by the filtration of impurities. The precipitation of aluminium hydroxide occurs when the solution, initially saturated at high temperatures, is cooled, leading to oversaturation. The addition of freshly precipitated aluminium hydroxide serves as nucleation points, facilitating the crystallization of aluminium hydroxide. This process is governed by Le Chatelier's Principle, which indicates that the backward reaction will consume aluminium hydroxide under certain conditions.

PREREQUISITES
  • Understanding of Le Chatelier's Principle
  • Knowledge of aluminium hydroxide precipitation mechanisms
  • Familiarity with the leaching process in metallurgy
  • Basic concepts of solution saturation and nucleation
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  • Study the mechanisms of nucleation in crystallization
  • Explore the implications of impurities in the aluminium leaching process
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Chemical engineers, metallurgists, environmental scientists, and anyone involved in aluminium production and processing.

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In the Leaching process of Aluminium, alumina present in bauxite dissolves forming a soluble sodium aluminate. The impurites are filtered off. The filtrate is diluted and a little freshly precipitated aluminium hydroxide is added which causes the precipitaion of aluminium hydroxide.

How does it cause the precipitation of aluminium hydroxide? According to Le Chatelier's Principle backward reaction will occur consuming aluminium hydroxide. What is the actual reason?
 
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The solution becomes over-saturated because the leaching is done at a high temperature, which is then lowered. Adding some solid aluminum hydroxide creates nucleation points for the precipitation.

(While we're on the subject, it's worth noting that those filtered-off impurities just spilled out all over in Hungary)
 
alxm said:
The solution becomes over-saturated because the leaching is done at a high temperature, which is then lowered. Adding some solid aluminum hydroxide creates nucleation points for the precipitation.

The solution becomes oversaturated with what? Aluminium Hydroxide?
Please elaborate 'nucleation points'.
 

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