Analysis of the reason why the alkalinity level of the saltwater is within the acceptable range, but it still contains calcium and magnesium?
Thread Content
During the purification of brine, the excess amount of sodium hydroxide in the brine reached 0.3 g/l, while the excess amount of sodium carbonate reached 0.6 g/l. The water coming out of the KAI membrane filter was also very clear; however, chemical titration analysis showed that this water still contained calcium and magnesium ions. This problem appeared suddenly, and its cause has not yet been identified. Could everyone help analyze what might be the reason? Thank you!
The formed calcium and magnesium precipitates are not properly separated, resulting in ultra-fine particulate calcium carbonate and magnesium hydroxide entering the refined brine. Be careful not to use too much alkali, as this can cause solid calcium and magnesium compounds to pass through the refined chelating resin column without being effectively absorbed by it. Strictly control the amount of excess alkali, as well as the pH value.
What is the concentration of calcium and magnesium ions in the brine produced by Kay membrane? Please describe it clearly. It could be due to an increased level of calcium and magnesium ions in the raw salt, or it might be caused by a leak in the membrane – there are various possible reasons. It is recommended to verify.
The 0.3 and 0.6 mentioned here represent the upper limits for our control parameters; yet this phenomenon still occurs when the actual values are at 0.2 and 0.5.
The concentration of calcium and magnesium ions in the effluent from the Kay membrane reached 10 mg/l (while our target value is below 4 mg/l). The content of these ions in the raw salt remained unchanged; even if their level in the raw salt increased, the fact that there was an excess of the two alkalis should prevent the effluent from having a high concentration of these ions. As for internal leakage in the Kay membrane, no turbidity was observed visually, and since we have three such membranes, it’s unlikely that all three would experience problems at the same time. Additionally, we installed a new set of membranes, and the effluent from this new set also showed similar levels. I don’t know what substances in saltwater can cause the levels to exceed the limits
Please pay attention to three points: 1. Is the reaction time sufficient?； 2. Is the reaction temperature within the normal range? ； 3. Check whether there is any leakage in the membrane module.
Thank you for your enthusiastic participation and communication: 1. The enterprise has been in operation for over a decade; if the reaction time is insufficient, it becomes apparent from the very beginning. Even after we reduce the flow rate of the brine (which effectively extends the reaction time), the problem persists. 2. The reaction temperature was intentionally increased by 2°C compared to the usual controlled temperature, and the same situation persisted. 3. We have three KAI membranes, and the same situation applies to all of them. Since all three KAI membranes were leaking, a new set was installed. The water output from the new membranes was analyzed and compared with that from the other sets, but there was no change – the situation remained the same.
If you check the scope of application of the EDTA titration method, you’ll see that it is not suitable for determining calcium and magnesium using the saline titration method
Is it possible to use spectroscopy to determine the levels of calcium and magnesium? From what I’ve heard in terms of analysis, sometimes heating the solution eliminates calcium and magnesium. If the output from the secondary brine resin tower is within acceptable limits, then the analysis results of the primary brine need to be questioned. If both the secondary and primary brines are not up to standard, it’s definitely a problem with the primary brine. The amount of alkali used is sufficient, and the reaction time is appropriate for an old system; although the reaction time should be reliable, it’s still a good idea to check whether there might be any short circuits in the reaction process.
Analyze the calcium and magnesium in past ionized water?
At this point, it's crucial to check what the SS of the water coming out of the membrane is