Rate of dissolution of sodium chloride into water

[CrudeDudeJr]

Thanks for taking a minute to try to help.

I am aware that the solubility of salt (NaCl) in water is 26% to 28% depending upon temperature.

But what I would like to know is how FAST the salt will dissolve (at a given temperature). I will need to do the same thing for anhydrous sodium carbonate. The make-up water is 1,500 TDS.

The idea is that a saturated solution can take a long time to create. And I don't need it to be saturated. I am creating stock solutions for a "chemical cocktail" make-up process and I need the solutions to be of consistent quality. The process is outdoors in the central US and temperature is a concern. We can control the residence time but we need to know what it will be so we can plan. Desired residence times might be on the order of 1 hour. We may need to heat the incoming water to be able to get consistent 6% sodium carbonate solutions. I don't know yet what the stock solution will be for sodium chloride but if someone could please point me to RATE data I would certainly be appreciative.

Thanks

Mark

 

[bimr]

You can use a brinemaker. Technical information:

http://www.brinemaker.com/salt-solubility.html

 

[cloa]

Rate is going to totally dependent on initial state of the physical state of the salt including minor contaminants - a solid block is going take a very long time to dissolve and finely divided pure powder dissolves quickly. It also depends on how you dissolve it- dump it in one place without agitation then it going to slowed by local concentration exceeding solubility. Low temperature also slows dissolution.

 

[CrudeDudeJr]

@bimr

Thanks, but that does not address my issue. I need Rate of Dissolution data. You see, I am making the briner. It's TIME that is important. I need accurate, known concentrations that are consistant throughout the year so I don't have to reprogram the process controls all of the time.

The longer I have to wait for a saturated solution the more storage I have to provide. And I need the concentration to be CONSTANT, not necessarily saturated.

I do appreciate you reading the post and offering your thoughts.

 

[CrudeDudeJr]

@cloa

You are correct to mention this. It's hard to put all of the details into the original request.

You can assume that I will be using finely granular salt and that we will be stiring the tank. I imagine using an eductor to introduce the salt into the water stream rather than dumping it into the tank. The salt is fairly pure food-grade product.

You are hinting at the problem when you mention temperature. My process it ourdoors in the midwest and we get some cold days. We are looking at the possibility of building a barn to house the storage, putting things underground, insulating tanks and heating them as necessary, etc.

All of this cost money and we want to do as little as is necessary. Thus the need for Dissolution Rate data. It surprises me that with salt being so common and used in so many processes (particularily food) that more of this data is not available.

Thanks for your comments and yout time.

 

[cloa]

Experiment at small scale.

There is data like this.

http://www.sciencedirect.com/science/article/pii/0022024881903778

Try contacting a salt institute

http://www.saltinstitute.org

 

[bimr]

What are you trying to accomplish and how much salt do you need?

You do not seem to understand how brinemakers work. You fill up the tank with salt, and concentrated brine is continuously taken out through a bottom underdrain. The available flowrate of the brinemaker is based on the size of the brinemaker. Brinemakers are also installed out of doors.

http://www.mortonsalt.com/faqs/industrial-faqs

For sodium chloride, there is only a small change in solubility with temperature.

http://www.chemguide.co.uk/physical/phaseeqia/saltsoln.html

Dissolution requires interaction between the molecules (or ions) of the solute and the molecules of the solvent. A finely divided solute will dissolve more rapidly than one that is in large chunks, because more contact is made between solute and solvent. Constant stirring increases the rate of dissolution, because stirring changes the particular solvent molecules that are in contact with undissolved solute. Because the solubility of solids and liquids generally increases with temperature, solids and liquids are often dissolved in warm solvents.

http://www.dot.state.oh.us/Divisions/ConstructionMgt/Materials/In House Research/NaCl.pdf

 

[CrudeDudeJr]

@cloa,

Thanks for this. The ScienceDirect paper may have useful info. Somehow I did not find that in my previous search.

I checked the Salt Institute but didn't find anything as technical as I require. I appreciate the suggestion.

 

[CrudeDudeJr]

@bimr,

Thanks for your suggestions.

I think I do understand how a brinemaker works, at least in a gross way. It is the specific details that I am after in this thread. You see, your suggestion assumes that the water taken off the bottom is saturated. That "available flowrate" is what I am after. Rather than believing a vendor that it will work and accept whatever size he tells me I need I want to prove it to the others in this project and control the sizing. Thus the need for Rate of Dissolution data. Certainly it is possible to "over-run" the briner (that is, draw faster than it can deliver) and this speed of dissolution is the heart of my question.

Thanks for taking the time to consider the issue.

 

[CrudeDudeJr]

@bimr,

The article from DOT Ohio is just the sort of thing I am looking for. That particular article did turn up in my previous search. Note that is does not deal with changing temperature or any of the intermediate concentrations before saturation. It does make clear that the method of agitation is important.

Thanks again ...

 

[bimr]

The AWWA standard for water treatment salt calls for 95% retainage by a #7 sieve and that the salt should dissolve rapidly without packing. Dry salt tends to pick up moisture and cake, that is why most prefer wet storage with a brinemaker.

in addition, I noticed that in the AWWA Water Treatment Plant Design book, there is a table that show the rapid mix tank residence time should be increased by a factor of 1.35 for 0 Deg F, where the base temperature is 20 Deg F with a factor of 1.

 

[CrudeDudeJr]

Thanks to @bimr and @cloa for the replies.

I did finally run across this reference:

"Dissolution Rates of NaCl and KCL in Aqueous Solutions", B. Simon, Journal of Crystal Growth, 52 (1981), 789-794

Additionally, Morton (salt) has some rules of thumb for designing brining tanks.

Interesting to me that there is not more hard technical data available for such a common substance and process. The brining tank rules of thumb must be good enough for most industries.