Precipitation of Li2CO3 at different temperatures

[seanshi40@gmail.com]

I have a simple solution of Li2CO3 with 7.5 g/L concentration. I need to simulate its precipitation when removing water from the solution at different temperatures. When running the simulation, the obtained results are different from my experimental results.

The problem is that according to simulation results, Li2CO3 precipitate much earlier, while experimentally, I found it starts to precipitate at water recovery factor of approx. 42%.

It is worth quoting that the same code already worked for other salts (precipitation of salts from brine), properly. I checked the results with published literature, and results were quite close.

Could you please advise me how I can follow up this case?

Best,
S

[dlparkhurst]

First, none of the databases distributed with PHREEQC have a Li2CO3 phase, so you need to make sure you have good thermodynamic data for the phase that precipitates.

Second, there are no LiHCO3 or LiCO3 ion pairs listed in any of the databases, and Li-CO3 interaction coefficients in pitzer.dat or sit.dat. So, I think the Li-CO3 system has not really been considered in any of the standard databases.

Perhaps you can find Pitzer interaction coefficients for Li-CO3 in the literature. You could then add them in pitzer.dat or your input file and retry your calculations. Similarly if you can find information for an ion-association model.

Finally, if it is not in the literature, you could use your data to estimate parameters for either the Pitzer, SIT, or ion-association approach.

[seanshi40@gmail.com]

Thanks for the reply.

Actually, I already updated the Pitzer data base for Li and the thermodynamic parameters were collected from the literature.

So, I will get Li2CO3 when using Equilibrium code in my simulation. However, the problem is that according to simulation results, Li2CO3 precipitate much earlier, while experimentally, I found it starts to precipitate at water recovery factor of approx. 42%.

So, got any suggestions, please?

Best,
S

[dlparkhurst]

Sometimes it takes a significant supersaturation before a mineral begins to precipitate. Often experiments try to bracket equilibrium by approaching from undersaturation and supersaturation.

There may be multiple polymorphs of Li2CO3, I don't know, but you may be precipitating a more soluble form that could later recrystallize to a more stable form that is represented by the log K you are using in the calculations.

If you believe your equilibrium states are accurate, I think it means that either the log K (and its temperature dependence) or the Pitzer parameters need to be adjusted. It is easier to adjust the log K. However, you should do a thorough search of the literature to determine if there are other estimates of the log K and Pitzer parameters.

[seanshi40@gmail.com]

Than you very much for your reply!