Treatment of high-salt, cyanide-containing ammonia nitrogen wastewater

The cyanide content is 500 mg/l, which contributes little to COD; what are the other impurities? Perhaps there are better oxidation methods, etc. Next, I will discuss membrane technologies used to remove ammonia and cyanide respectively. The technology used is the supported air film technology. If the pH is greater than 8, first adjust the pH to below 8, and pass the wastewater through the tube side of a polypropylene hydrophobic microporous hollow fiber membrane module, while allowing it to flow counter-currently through a dilute sodium hydroxide solution (with a pH greater than 11). In this way, hydrogen cyanide is irreversibly absorbed by the membrane. If the pH of the wastewater remains at 8, or even below 7, throughout the process, 99% or even 99.9% of the cyanide can be removed and concentrated in the absorption phase (by dozens or even hundreds of times). But I don’t know how to deal with an aqueous solution of sodium cyanide containing alkali. After removing cyanide, the pH is adjusted to above 11.5, and the wastewater is passed through the tube side of another polypropylene hydrophobic microporous hollow fiber membrane module, while dilute sulfuric acid solution (with a pH always kept below 5) flows counter-currently through the shell side; in this way, free ammonia is irreversibly absorbed by the membrane. If the pH of the wastewater remains above 11.5 throughout, 99% or even 99.5% of the (total) ammonia can be removed and concentrated in the absorption phase (resulting in an aqueous solution of 25% sulfuric acid, which represents a concentration of ammonia over 50 times higher). Sulfuric acid an can be treated with a base and then ammonia can be distilled off to obtain high-concentration ammonia water or liquid ammonia for reuse, or it can be sold as a fertilizer. If information is available on other impurities in the wastewater, such as volatile organic solvents, there are corresponding recovery techniques available. This wastewater, with COD reduced to below 50 ppm and total ammonia nitrogen below 1 ppm, can be used for the production of chlor-alkali. We provide large-scale polypropylene hydrophobic microporous hollow fiber membrane modules and related engineering services. For interest, please contact yjqin1@yahoo.com or yqin@chembrane.com

Treatment can be carried out using stripping and ammonia vaporization processes! ! !

Vapor ammonia + electrolysis should be able to handle it! ! !

For the two students upstairs, using steam requires at least 15 yuan per ton of wastewater to be treated, while the membrane method incurs costs of less than 4.3 yuan per ton for acid and alkali treatment. As for power consumption, the membrane method is below 2 degrees, while the ammonia distillation method is at least 2 degrees or higher. Using the ammonia distillation method in a tower, the concentration of ammonia at the tower top is very low; whereas with the membrane method, the concentrated sulfuric acid byproduct can be treated with alkali and then simply stripped to obtain an ammonia concentration of nearly 30%.

The pH value of the wastewater effluent is between 3 and 4; in addition, the wastewater may contain sodium formate. We have tried to use membrane treatment methods, but some membrane suppliers rejected this approach due to the high concentration of sodium chloride in the water. I’m not sure what requirements the membranes mentioned by the experts have regarding salt corrosion – whether they can be used for water like ours. If you are interested, you can send me an email at ykwd24@126.com

“The pH value of the wastewater effluent is between 3 and 4. That’s great; HCN can be removed easily using support gas membrane technology (membrane desorption-chemical absorption). Within this pH range, it is not difficult to reduce HCN to 10 ppm, or even below 1 ppm. “The pH value of the wastewater effluent is between 3 and 4; furthermore, the wastewater may contain formic acid. The pKa of formic acid is 3.75; that is, when pH=3.75, 50% of the formic acid exists in its free form ； The lower the pH, the more formic acid exists in its free form. Therefore, although the relative volatility of formic acid in dilute aqueous solutions is much lower than that of hydrogen cyanide, the aforementioned support gas film technique can still remove a small amount of formic acid, thereby reducing the COD to some extent. It is certain that 18% sodium chloride has a strong salting-out effect on HCN and NH3 (which will **reduce equipment investment and operating costs**); it also has a salting-out effect on HCOOH, but this effect is not significant. In short, the presence of high concentrations of sodium chloride has no adverse effect on the removal of HCN, HCOOH, and NH3 using the supported gas membrane technique. Furthermore, our polypropylene hydrophobic microporous hollow fiber membrane modules can handle salt solutions below the saturation concentration (27% NaCl), 35% hydrochloric acid, 40% sulfuric acid, and 30% sodium hydroxide without any problems, even at temperatures just below 60 degrees. However, membrane modules are not resistant to oxidizing agents, surfactants, emulsified oils, and suspended solids, which must be removed in advance. I’m not sure about the level of these impurities in your wastewater. The removed HCN and HCOOH exist in the form of concentrated salts, and can be treated using advanced oxidation processes. The wastewater from which the vast majority of HCN has been removed has its pH adjusted to above 11.3, after which the support gas film technology can be used again to remove, separate, recover, purify, and concentrate it to obtain ammonium salts. If the conditions are suitable, we can go to the site to demonstrate the process after the New Year.

yiqin1: We would be very happy if it were possible to recover HCN, as I need 15% NCN in my production process; therefore, using alkali for absorption is completely feasible. Could you send me the detailed information about your company via email? I will get in touch with you as soon as possible; our company is very eager to carry out this task.

At the initial pH value, it is possible to remove HCN to levels of 10 ppm or even below 1 ppm using the membrane-permeation desorption-chemical absorption technique. After raising the pH to 11.5, it is possible to remove NH3 to levels of 10 ppm or even below 1 ppm using membrane-permeable desorption-chemical absorption technology. I need to conduct experiments to find out exactly how much formic acid can be removed when removing HCN. Some information I have at hand suggests that 18% sodium chloride has a quite significant salting-out effect on formic acid. It will depend on the test results at that time.

Hello yjqin: When using membrane desorption-chemical absorption technology to remove HCN, where does the HCN go? Does the entire process need to be carried out in a sealed environment? Please explain it.

Please note that the pKa of hydrogen cyanide is 9.21; this means that at a pH of 9.21, half of it is dissociated. Therefore, at pH values of 3–4, it exists almost entirely in its molecular form. If the original wastewater is passed through the tube side of a polypropylene hydrophobic microporous hollow fiber membrane module, while a dilute sodium hydroxide solution (with a pH greater than 11) flows counter-currently through the shell side, then hydrogen cyanide is irreversibly absorbed across the membrane. If the pH of the wastewater remains at 8, or even below 7, throughout the process, 99% or even 99.9% of the cyanide can be removed and concentrated in the absorption phase (by dozens or even hundreds of times). It should be noted that the standard procedure involves stripping HCN using gas, and then absorbing it with an alkaline solution; this requires two towers. But if I use a polypropylene hydrophobic microporous hollow fiber membrane module (membrane contactor), one membrane module can serve the function of two towers, increasing the mass transfer driving force, reducing the mass transfer resistance, lowering investment costs and energy consumption, and preventing gas leakage contamination. As for HCN, it naturally turns into sodium cyanide. Didn’t the original poster say that this is their raw material for production? The entire process is similar to the indirect heat exchange in shell-and-tube exchangers; as long as there are no leaks in the wastewater, it isn’t necessary for the whole process to be airtight.