Can sodium chloride extracted from saline wastewater in fine chemical industries be used in chlor-alkali production?

It can be separated first to test the relevant indicators. Decide again!

It’s easier to make a judgment once you know what product is being produced and the manufacturing process.

1. Regarding TOC in saline, small molecules can be treated, but it seems there are no effective solutions for benzene rings； 2. Other metal ions in the brine can all be removed during the brine purification process ； 3. Total ammonium, including inorganic and organic ammonium, mainly affects nitrogen trichloride in the chlorine gas within the electrolyzer ； 4. The impact of other impurities on the diaphragm – surely they’re not meant to be used in ion exchange membranes?

This is a systems engineering project: 1. It is theoretically feasible to use； 2. It depends on the amount of impurities that affect the ion exchange membrane; one thing is certain: the salt obtained through extraction must be processed to reduce the levels of harmful components to those required by the standards for the raw salt (or blended salt) ； 3. The main impurities include TOC (as mentioned by the guy upstairs), TN, TP, etc ； 4. To achieve industrialization, pilot tests, scale-up tests, and membrane evaluations are also required, and this process will not take short time ；

How are these indicators measured? What is their maximum value? I would like to check whether the sodium chloride obtained through evaporation and crystallization can be used. Could you please tell me? Thank you

Care must be taken when using such saltwater as a raw material. It seems that the standards for refining saltwater used in the past were designed for refining crude salt, with no specific requirements regarding certain small organic molecules. There are no reports or analyses available on whether these small molecules have an impact on the membranes or the quality of the product. If possible, it is still advisable to conduct pilot tests, as it would be a shame not to recycle such salts.

With the current technical level in China, it is very difficult to completely remove the impurities from them; some amount of impurities will always remain, and this has a significant impact on the ion exchange membrane. Since ion exchange membranes are relatively expensive, it is recommended not to consider using them. The diaphragm electrolysis system could be considered as a viable option; it seems that several chlor-alkali manufacturers in China have adopted diaphragm caustic soda production to handle wastewater. Generally, as long as the ammonia nitrogen level is well controlled (inorganic ammonia ≤ 1 mg/l, total ammonium ≤ 5 mg/l), there should be no problems. The only downsides are higher consumption, more frequent tank cleaning, and higher costs. By controlling the ratio of asbestos fibers, it should be possible to keep the costs within an acceptable range. Of course, the prerequisite is that the diaphragm electrolysis system and your factory belong to the same company; otherwise, no manufacturer will accept it. Another option is to make a very large one-time investment. Before the New Year, a manufacturer from Guangdong came to our factory to promote a technology (a European technology) that is said to be able to generate hydroxyl radicals. Hydroxyl radicals have strong oxidizing properties and can oxidize all organic substances, producing CO2 and water. A set of such equipment requires little space, around 100 square meters. The investment amount varies from several million to tens of millions depending on the specific circumstances, and reagents provided by Europe must be purchased as well. If the value added of the products manufactured by your factory is high, it could be considered. The above are merely personal opinions.

Recommended solution: First, remove/recycle organic substances (volatile/semi-volatile/non-volatile, polar/non-polar, acidic/alkaline). We have available and effective technologies for such removal/recycling, which meet the requirements of the chlor-alkali process. Secondly, this low-investment, energy-efficient thermally driven membrane process can concentrate brine to 20–24% while recovering high-quality fresh water. We have developed a process that can be used to concentrate highly saline aqueous solutions. This process operates without the need for high temperatures, high pressures, or negative pressure (or vacuum), and it is noise-free. If the temperature of the wastewater is below 40 degrees, this process can use a low-temperature heat source (60–120 degrees) as a driving force; yet its heat efficiency (water production ratio) is much better than that of multi-stage flash evaporation and multi-effect evaporation. When the wastewater temperature is between 70–100 degrees, this process can recover over 50% of the water content while simultaneously concentrating the brine, without the need for an external heating source. The electrolyte concentration in the fresh water produced by this process can be as low as less than 1 ppm, with typical values ranging from 10 to 100 ppm. Another advantage of this process is that the equipment used is mostly made of plastic, which eliminates the corrosion problems associated with multi-stage flash evaporation and multi-effect evaporation processes. The equipment required for this process is relatively compact, similar to that used in reverse osmosis; therefore, for a given separation task, the volume of equipment needed is much smaller than that required for multi-stage flash evaporation and multi-effect evaporation. As mentioned earlier, even in the absence of high temperature and pressure or negative pressure (or vacuum), the thermal efficiency of this process (water production ratio) is still better than that of multi-stage flash evaporation and multi-effect evaporation; it is 8 to 15 times higher than that of the membrane distillation process I developed 20 years ago. Furthermore, the investment in this process is also low. The total cost of this process (equipment depreciation, electricity and heat consumption, etc.) is around 10 yuan per ton of wastewater, while the output value is between 40 and 60 yuan per ton of wastewater. If you are interested, feel free to contact me. My email addresses are: yqin@chembrane.com or yjqin1@yahoo.com.