[teknofly]

I'm trying to figure out how it would be possible to separate the two (lead nitrate and nickel sulphate). The two compounds are in a pile and need to be separated into two separate piles (one of lead nitrate and one of nickel sulphate). My first problem is if i were to disolve the two a stable lead sulphate would be formed which would make it difficult to return it to pead nitrate. I was thinking along the lines of using an iodide to extract the lead and then a hydroxide to precipitate the nickel.
I think i'm going down the wrong path but now that these ideas are stuck in my head i'm finding it dfficult to find alternatives. Any ideas at all??

[Mitch]

What are the melting points like?

[teknofly]

i was thinking of something like that. but was unsure how i would create an environment to prevent the creation of oxides.
mp of lead nitrate - approx 740K
     of nickel sulphate - approx 440K* (hexahydrate compound)
                dry - decomposes at 1100K

[Mitch]

Oxide formation usually doesn't begin untill your above 300 degrees celsius. 400-500 is getting a bit risky, but I don't know definitively for these 2 examples.

[Alberto_Kravina]

I was thinking along the lines of using an iodide to extract the lead and then a hydroxide to precipitate the nickel.

That's not really a good idea....lead(II)iodide is an insoluble (in water ) precipitate, but it is soluble in excess I^- as a tetraiodo complex....

Pb²⁺ + 2 I^- ----> PbI_2(s)

PbI_2(s)  +  2 I^-  ----> PbI₄^2-

Try to precipitate the nickel as Ni(OH)₂ with NaOH (lead hydroxide is soluble in excess NaOH as a tetrahydroxoplumbate(II)- complex). After separation (by filtration) of the nickel hydroxide precipitate the Pb²⁺_(aq) with potassium chromate.

Roast the nickel hydorxide:

Ni(OH)₂ ------> NiO + H₂O

Dissolve in sulfuric acid:

NiO + H₂SO₄ ---> NiSO₄ + H₂O

Nickel sulfate forms.

I'll post more later, I'm in a rush!

[Borek]

Try to precipitate the nickel as Ni(OH)₂ with NaOH (lead hydroxide is soluble in excess NaOH as a tetrahydroxoplumbate(II)- complex). After separation (by filtration) of the nickel hydroxide precipitate the Pb²⁺_(aq) with potassium chromate.

Not so easy. As teknofly wrote once both salts are dissolved PbSO₄ precipitates. Thus after adding hydroxide you will have two precipitates (IMHO lead is not so amphoteric that it will dissolve).

teknofly: perhaps you may find some way of complexing lead (or nickel)?

[teknofly]

Still throwing around the idea and have come to:

step 1: dissolve them both in water extract ppt
Result: Nickel nitrate (in solution) and lead Sulphate (ppt)

step 2: lead forms a very soluble lead acetate complex ion therefore dissolve in acetic acid and addition of barium nitrate to remove sulphate (filter off).
Result: lead acetate in solution (with nitrate) with barium sulphate (ppt)

step 3: neutralise using an organic base (pyridine??) and extract aqueous layer
Result: lead nitrate solution  (i think)

step 4: add dilute sodium hydroxide to ppt NiOH
result: NiOH ppt

step 5: disolve in sulphuric acid and boil dry
result: Nickel sulphate (i hope)

This actually sounds pretty unrealistic to me but i'm grasping at straws here... any further thoughts would be highly appreciated!!

[Alberto_Kravina]

Not so easy. As teknofly wrote once both salts are dissolved PbSO4 precipitates. Thus after adding hydroxide you will have two precipitates (IMHO lead is not so amphoteric that it will dissolve).

teknofly: perhaps you may find some way of complexing lead (or nickel)?

True! my mistake! but after dissolving the two salts you can try to dissolve the precipitated lead sulfate in NaOH or 99%- actetic acid.
Afterwards you can mix this two solutions and separate the two ions.  

[teknofly]

Ahhh the joys of a good nights sleep.
after a little further investigation:
lead nitrate soluble in Alcohol (not great but soluble none the least)
Nickel sulphate - hydrated - soluble in alcohol
                      - anhydrous - insoluble in alcohol

Theory is:
1. dry the sample through roasting/dessicator etc...
2. disolve in alcohol filter off ANHYDROUS nickel sulphate
3. evaporate alcohol from lead nitrate
4. disolve nickel sulphate in water, filter(any ppt out) and evaporate

thats about all i've got