Sodium Hydroxide Agitation

[renzon]

I need to come up with a way to agitate 3lbs of NaOH/1 gallon of water solution. We are working with a 200 gallon tank.

Our first reaction was to air agitate but the solution must stay at about 150-180F, I think. So really air agitation sounds like it is going to cool the solution off rather than help move the solution around. Does any one have any ideas?

Recently we retrofitted an immersion tank with a 1hp pump and 1" copper pipe to constantly circulate and agitate a cleaning solution that also required heat. I would like to do something along the same lines to the NaOH tank but I am afraid the pump will not last and an acid specific pump will be too expensive.

 

[moltenmetal]

Sodium hydroxide is base, not acid.

We're presuming that an ordinary over-the-side agitator won't work here because the tank doesn't suit its installation- if not, that's probably your cheapest option. There's not much more to them other than an electric motor, a mounting bracket, a chuck and a thin stainless shaft with a marine prop on the end. No matter: NaOH dissolves readily. There will be a significant heat of dissolution when dissolving this much NaOH, so don't forget about this.

Provided the NaOH and water you are using is not contaminated with too much chloride or anything else, ordinary 316 stainless steel will be fine, as will many of the non-metallic materials such as polypropylene. You can get a plastic magdrive or (better still) air double diaphragm pump to do your agitator for cheap. Drum pump versions exist, so you can just insert it through a nozzle in the top head and return the transfer hose to another nozzle.

 

[chief]

You can pick up a paint drum agitator in any hardware store , which will do the job fine.

Offshore Engineering&Design

 

[Latexman]

Caustic is very corrosive to humans. I recommend a system that is as closed as you can get. You need a process and procedure that minimizes risk of exposure. Let me extrapolate from previous ideas, a paint agitator on the end of a hand held drill is not safe in this case.

Good luck,
Latexman

 

[renzon]

Sorry about the acid/base mix up...


You are right; a hand held drill agitator will not really help out for a couple of reasons. First, the operator will need to place parts in and have one hand free to control the basket. Two, the operator will need to have the ability to place parts in and then walk away to do other jobs while the parts soak in the solution. Finally, there is the safety issue which has already been brought up.

As much as I would like to make it a simple hand drill agitator I don’t think it will work. I thought about something that could be placed at the bottom of the tank and would spin or move back and forth like a washing machine to keep the solution moving, what do you all think? My only concern is the over the side heating element will get in the way.

 

[jdarco]

You could use a small centrifugal pump (the mag drive mentioned earlier is a good choice) with a couple eductors in the bottom of the tank to provide continous mixing. The nice thing about the eductors is no moving parts! If you do use the mag drive pump, make sure they trim the impellar for the higher specific gravity.

 

[renzon]

Great! Can i find the mag drive at grainger,msc, or mcmaster carr? Suggestions? What about price? Ill try to look more into them tomorrow in the AM. Appreciate all the input.

 

[Latexman]

Are you using NaOH prills or a concentrated solution? If prills, you want to keep them out of the suction line and pump or it'll choke the flow and maybe damage the pump. It's a good argument for using liquid.

Good luck,
Latexman

 

[moltenmetal]

A plastic air diaphragm pump will move lots of liquid and won't care about the solid, unlike the magdrive centrifical. That's still my recommendation if you don't want a proper agitator. You can get them from McMaster Carr but they'll be cheaper from somebody who actually sells pumps directly. Tons of brands- Wilden, Sandpiper etc.etc.

Mixing venturies are cheap enough and will help you turn pump discharge pressure into flow. Stick one on the end of the discharge pipe/hose- that'll do the job.