HNO3 Waste Treatment
Q. Recently we have problem in treating the HNO3 in our customer waste treatment facility. The HNO3 content is lesser 30% from the inlet compare to the outlet. We need more than 90%. This is a alkaline Sn immertion plating plant.
Thank you for your prompt advice.
A. HNO3 does not exist as HNO3 in alkaline solutions, it exists primarily as the salts of the various cation metals, like NaNO3. The problem you have is that almost all nitrates are soluble in water. It is very difficult to remove.
a few exceptions are:
"Even Pb(NO3)2 is soluble to 38 ppm in "cold" water and 130 ppm in "hot" water, while Ba(NO3)2 is soluble to 5 ppm in "cold" water and 34.2 ppm in "hot" water, and Sr(NO3)2 is soluble to 40 ppm in "cold" water and 100 ppm in "hot" water where "cold" water is generally 3 degrees C and "hot" water is generally 95 degrees C."
Unfortunately Pb is worse than NO3 in the discharge and Ba and Sr are not much help either.
Reverse Osmosis, Distillation, Ion Exchange, Electro Dialysis, and Biological waste water treatment systems are the primary ways to remove nitrates (NO3). In many cases it is more cost effective to keep the NO3 out of the waste water by recycling the acid and or the first rinse back the acid or plating bath thus minimizing the amount of NO3, nitrate in the waste water to begin with.