Chemical precipitation

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Chemical precipitation means formation of a solid substance: soluble metal ions are converted into an insoluble form by changing the composition of the aqueous solution so that the solubility of the metal ions is reduced. The solid particles formed by this reaction can then be separated and removed from a solution by settling and/or filtration.

Chemical precipitation is used for removal of both impurities and wanted metals from leaching solutions and to remove impurities from process wastewaters (solution purification or metal recovery). When the desired metal is precipitated it is usually treated further before a desired product, metal or metal salt, is obtained.

Different types of precipitation

Precipitation is achieved by the addition of proper reagents (alkali, salts) and can under correct conditions be done selectively. Common chemical precipitations used are hydroxide- and sulfide precipitation.

Factors affecting chemical precipitation

  • type and concentration of metal ions present in solution
  • precipitant/precipitating reagent, for example hydroxide or sulfide
  • reaction conditions (pH, temperature, redox potential, etc.)
  • presence of other constituents like complexing agents that may inhibit the precipitation reaction.
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