Mrs. Wages "Leftovers"

[hyperfocal]

I've always used Mrs. Wages Pickling Lime in my kalk reactor. As the lime depletes, a very fine white powder accumulates in it's place. I've always assumed that the power was calcium carbonate created when air inevitably made it's way back into the reactor.

Today I collected some of the sludge, ran it through a coffee filter and dried the remains in the sun. Once it was dry, I added some to vinegar expecting it to react like aragonite does... well, it didn't. No reaction at all.

It's very fine, white, and insoluble in water or vinegar. I've done a bit of poking around online and I think it is talc -- presumably added by the manufacturer to make the calcium hydroxide easier to handle and package.

If it is talc (hydrated magnesium silicate) I think it's reef safe but would feel better getting confirmation from the experts. If it's not talc, any idea what it might be? And, does the bulk aquarium-grade calcium hydroxide available have similar "leftovers"?

[redfishsc]

Very interesting.

I wonder if the talc could be a source of silicates in the reef tank. Not that it's a huge deal, silicates alone won't cause any diatom blooms (gotta have nitrate/phosphate too). May cause proliferation of some sponges though.

[jeepguy242]

I have experienced this also, i looked at my new DIY kalkwasser reactor after i started running it and i always saw white powder in the bottom of it, and i thought, "oh, its been a week or 2 and its still got pickling lime in it, it must not need more yet", but then one day my ph and alk started to drop and i looked real close at the reactor and it just didnt quite look right, so i dumped it out and re filled it with fresh lime and noticed that the fresh looked WAY different than the stuff i just dumped out, also the old stuff settles alot more quick.

[Randy Holmes-Farley]

Why do you think talc is added? In a food product, if it is not listed on the label, I do not think it can be legally added at any level.

The residue from lime is typically a number things, including magnesium hydroxide, and not all of these will bubble. I discuss the residue in these articles:

Magnesium and Strontium in Limewater
http://www.advancedaquarist.com/issues/dec2003/chem.htm

What is that Precipitate in My Reef Aquarium?
http://reefkeeping.com/issues/2005-07/rhf/index.htm

from it:

http://reefkeeping.com/issues/2005-07/rhf/index.php#9

Precipitates on the Bottom of Limewater Reservoirs
The solids on the bottom of a limewater reservoir (Figures 5 and 7) contain everything that did not dissolve, or that dissolved and later precipitated from solution. Such solids could contain magnesium hydroxide and carbonate, calcium hydroxide and carbonate and a variety of other impurities such as copper salts, alumina, silica, etc.

In order to determine what is in these deposits, I tested a sample of the white solid material that had been collecting for months on the bottom of my limewater reservoir, and detailed the results in a previous article. I removed the white sludge along with some limewater. The mixture of solid and liquid was acidified to dissolve it, and it was tested for calcium, magnesium, and strontium. The results are shown in Table 1. Only relative concentrations are shown as no effort was made to dry the sample prior to analysis, making absolute concentrations meaningless.

As anticipated, based on the very low solubility of magnesium hydroxide and the high concentration of hydroxide ion in limewater, the solid material on the bottom of the limewater is enriched with magnesium. Relative to calcium, magnesium is enriched by a factor of 13 in the sludge compared to the solid starting quicklime. This magnesium may be present as both magnesium hydroxide and magnesium carbonate, but because magnesium carbonate is fairly soluble compared to calcium carbonate, it is most likely that the primary magnesium salt is magnesium hydroxide. It may also be mixed calcium and magnesium carbonates.

Interestingly, strontium is actually depleted by a factor of two relative to solid starting quicklime, indicating that it is less likely than calcium to end up on the bottom of the reservoir. While strontium carbonate is somewhat less soluble than calcium carbonate, the strontium concentration in the limewater is so low that SrCO3 may not actually be saturated, so it may not precipitate at all. The strontium that is there may simply be copreciptiated with calcium carbonate.

The solids on the bottom of a limewater reservoir or the residue left in a limewater reactor can also contain other materials. Phosphate, for example, would be insoluble in limewater, precipitating as calcium phosphate. Many toxic metals, such as copper, are also insoluble in the high pH of limewater, forming carbonates or oxides. These metals can also bind directly to undissolved lime or to calcium carbonate precipitates, as I showed in a previous article. In a sense, this precipitation can purify the limewater so that in some cases it may be even purer than the starting water or lime.

This purification is also seen in practice by many aquarists who have noticed the solids on the bottom of their limewater containers discolor, often to a bluish/green color suggesting copper. For these reasons, I recommend that lime solids not be dosed to aquaria when it is possible to avoid it. Letting the limewater settle for a few hours to overnight will permit most of the large particles to settle out, and whether it looks clear at that point or not, it is likely fine to use. In general, it is a good practice to leave residual solids on the bottom of limewater reservoirs rather than cleaning them out every time, as they may actually help purify the water by these precipitation mechanisms. Once the solids discolor, or have been collecting for 6-12 months, however, they should be discarded.

[hyperfocal]

Why do you think talc is added? In a food product, if it is not listed on the label, I do not think it can be legally added at any level.

Why talc? It just fit what I knew at the time... White, greasy-feeling, didn't dissolve in water or vinegar and had a pertinent real-world application (as a glidant). I also thought that the relatively large volume of the residue was too great for it to be impurities. Definitely some working backwards from the conclusion going on :)

I checked the Mrs. Wages site (http://store.mrswagesstore.com/mrswagpiclim.html) and they're quite up-front about how their pickling lime is "Food grade calcium hydroxide with no additives or preservatives." Seems pretty definitive.

Next time I clean out my reactor (in about 7 weeks) I'll do a better job of collecting the residue. I'm curious what the mass of the gunk is. In the bottom of the reactor, it takes up a lot of room (2x the volume of 1 lb of "fresh" pickling lime") but it is a lot more buoyant than the lime; I (once!) accidentally let a little escape into my sump & display and a few drops turned my tank into milk in a matter of seconds.

Thanks for the info, Randy :)

[Randy Holmes-Farley]

:thumbsup:

Happy reefing. :)