[curiouscat]

I was looking for a flocullating agent that'd be stable at high pH (~11). Normally, I'd use Alums, Ferric / Ferrous Chlorides or Sulfates but all of those seem to work best at neutral or slightly alkaline pH (pH 7-8.5 mostly reported).

Any ideas  which other agents might be good to try? The stream to be treated is  Oil + CaCl₂ + H₂O composition but with ~10% of suspended inorganic solids in it mostly CaCO₃.

The particle sizes are fairly large; 50 microns and larger. The solids separate out easily in a lab centrifuge at modest g / rpm values.

I've seen Polyacrylamides reported as flocculating agents but not sure what their basic medium stability is.

[billnotgatez]

From a ceramics source

The most common flocculants potters use are epsom salts (magnesium sulfate) and calcium chloride, though acids (such as muriatic acid) can also be used

I assume this does not apply in your case.

[curiouscat]

From a ceramics source

The most common flocculants potters use are epsom salts (magnesium sulfate) and calcium chloride, though acids (such as muriatic acid) can also be used

I assume this does not apply in your case.

I could try magnesium sulfate. CaCl2 I already have oodles of right in there.

HCl's a no go. Cannot go to acidic pH. The oily phase needs to remain alkaline for stability reasons.

[billnotgatez]

Is it typically true, that a base environment is deflocculating and going towards neutral is flocculating?

[curiouscat]

Is it typically true, that a base environment is deflocculating and going towards neutral is flocculating?

Never heard of that. But its a complex field and I'm no expert.

I doubt the trends are monotonic. From what I read a lot of water treatment flocs form best between pH 7-8.5.

[curiouscat]

I tried adding potash alum (KAl(SO₄)₂.12 H₂O) and there seems a gelatinous ppt that forms. Wonder if this might be AlCl₃?

Al₂(SO₄)₃ + 3  CaCl₂  2 AlCl₃ +  3 CaSO₄

Is this reaction to be expected?

[Borek]

Gelatinous in the context of presence of Al makes me think about Al(OH)₃.

[curiouscat]

Gelatinous in the context of presence of Al makes me think about Al(OH)₃.

You must be right. AlCl₃ has a high solubility in H₂O. Al(OH)₃ does not.

I wonder what'd be a good flocculating agent in this situation. I suppose Fe-chlorides and Fe-sulfates will form hydroxide ppts too. 

[billnotgatez]

http://www.flocculants.info/polymer-definitions.html

This page suggests
calcium salts at pH between 4 and 14
iron salts at pH between 4 and 13
aluminum salts at pH between 4.5 and 10

If you use
Polyethylene-imines
Polyamides-amines
Polyamines
Polyethylene-oxide
are we then talking organic chemistry?

[curiouscat]

http://www.flocculants.info/polymer-definitions.html

Thanks @bill! That looks like a great site. 

[billnotgatez]

Potters flocculate alot 

[ajkoer]

Try Ammonium iron(III) sulfate, NH4Fe(SO4)2·12 H2O, also known as ferric ammonium sulfate (FAS) or iron alum. Highly soluble and less acidic than Aluminum sulfate.

Now in the presence of CaCl2. I think we get NH4Cl, CaSO4 and Fe(OH)3. Also, I like the idea of an ammonium salt with oil (also presence).