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Author: Subject: Precipitation of metal hydroxides and carbonates

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[*] posted on 20-7-2017 at 02:00
Precipitation of metal hydroxides and carbonates

In a solution a metal carbonate is dissolved if pH is raised used NaOH ?
what will precipitate Metal hydro-oxide or metal carbonate ?
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[*] posted on 23-7-2017 at 20:02

Short answer: the carbonates would probably precipitate first, and then the hydroxides if there's still metal ions remaining since carbonate is a divalent ion.

Long answer: doing some equilibria calculus, you could set the pH of the solution, find the relative carbonate concentration at that pH and then compute the concentrations of the metal, the carbonate ions and hydroxide ions for the carbonate added. Then you could check whose Kps is exceeded.
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[*] posted on 1-8-2017 at 05:27

Removal of soluble heavy metal ions from wastewater is a common industrial treatment requirement. Examples of the industrial processes that generate waste streams containing heavy metals are:

Electroless Nickel plating
Printed circuit board manufacturing
Metal forming operations
Battery recycling
Mining operations
The concentration and chemical form of the soluble heavy metals in the wastewater stream varies with the industry and the mix of operations at a processing site.

Typical removal strategies involve precipitating the metals in an insoluble form such as hydroxides, sulfides, carbonates or some combination, then removing the precipitate with tubular microfiltration for very high quality filtrate, or conventional clarification. The resultant sludge is collected, thickened and dewatered for landfill disposal.

Hydroxide precipitation is a common method as it is relatively simple to operate. Sulfide precipitation has some advantages, but pH and oxidation-reduction potential (ORP) must be carefully controlled to minimize the risk of producing toxic levels of hydrogen sulfide gas. Using hydroxide and sulfide precipitation, in two sequential steps, is also an option, particularly where complexes or chelates are present. Carbonate co-precipitation, using sodium or calcium carbonate, can also be helpful, for instance, for soluble lead reduction; lead carbonate is essentially insoluble (0.00011 g/100 mL @20°C) and will precipitate out. Phosphate precipitation is also an option although this is not such a common process.

Hydroxide Precipitation

Hydroxide precipitation is initiated by adding an appropriate hydroxide to the waste water in stirred reaction tanks to form the insoluble heavy metal hydroxide precipitates:

M+n +nOH- M(OH)n

Many of the heavy metals show marked amphoteric behavior; their hydroxides reaching minimum solubility at a specific pH for each metal.

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[*] posted on 2-8-2017 at 13:25

If you want to filter out the precipitate, carbonate is preferrable, because hydroxides are often slimy or gel-like and hard to filter, and carbonates are conveniently in powder form.

Smells like ammonia....
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