In salt-lake lithium evaporation and concentration, how do you judge the end point?

Conclusion first

Judge the end point by three crossing lines: inline density (with temperature compensation), inline conductivity or boiling-point elevation, and periodic lab sampling of lithium concentration and impurity ratios. Relying on time or visual experience alone guarantees batch-to-batch differences.

Why one parameter is never enough

Criterion	Strength	Limitation
Inline density	Continuous, fast response	Affected by temperature and solids
Conductivity	Cheap, easy to maintain	Sensitivity drops in the high-salt range
Boiling-point elevation	Directly related to concentration	Affected by vacuum and pressure fluctuation
Lab sampling	Definitive composition	Lagging, low frequency
Fixed schedule	Simple	Blind to feed variation; high risk

Density is the most common continuous criterion, but temperature compensation is mandatory. A few degrees of brine temperature change can mask the true concentration change in the density reading.

Common field problems

• Scaling: salt deposits in the evaporator and the density meter’s measuring cell; readings drift slowly fictional
• Bubbles: in boiling service bubbles enter the cell and read density low
• Solids: precipitated crystals make “density” no longer equal “concentration”
• Corrosion: high-chloride brine is unkind to metal wetted parts; wrong material choice means frequent shutdowns

Treat different brine systems differently

Chloride-type, sulfate-type and carbonate-type brines precipitate salts in different orders, and the density range at the end point differs accordingly. Copying another project’s end-point values is a classic mistake. Calibrate against this project’s own brine composition.

When the density criterion fails

• Heavy salt precipitation with solid-liquid mixing
• Significant vacuum fluctuation
• Measurement point in a dead zone or bubble accumulation area
• Density meter not calibrated for a long time

How to implement

1. Build this project’s own “density–lithium concentration” curve from lab data
2. Fit the density meter with inline calibration or periodic offline comparison
3. Put vacuum, temperature, feed flow and density on the same trend screen
4. Raise sampling frequency near the end point and confirm manually

Automation reduces variation, but end-point confirmation still needs composition data behind it.

Scaling and maintenance

Instrument maintenance in evaporation service is essentially anti-scaling work: periodic flushing, lowering the cell temperature, choosing fouling-resistant structures, and building cleaning into the production rhythm.

Material reminder

High-chloride brine is unkind to stainless steel; prefer non-metallic or specialty-alloy wetted parts. The typical symptom of a wrong material choice is pitting perforation within months, not uniform thinning.

How to use the data

Put density, temperature, vacuum and feed flow on the same time axis and the end point becomes much clearer. Reading density alone invites misjudgment by temperature and bubbles.