veerenyadav
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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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Betta
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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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Lena01
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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:
Electroplating
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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ave369
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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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