Question

I am managing an HSE project to dispose of an expired NaHS solution. There was approximately 500 gallons of liquid in two tanks. Both tanks have been pumped down, and there is little residual liquid with ~ 100lbs of solid in the bottom of the tanks. The H2S readings in the tank are approaching IDLH conditions. I am assuming that over time, the pH of the NaHS solution decreased due to exposure to air which is causing the high concentration of H2S in the tank. We want to suppress the H2S vapors so that when the solids are placed in drums for disposal, there won't be any off gassing in the headspace of the drum. Would adding solid sodium carbonate to the solid in the bottom have any adverse reaction?

Answer 1

Adding sodium carbonate to the residual NaHS to mitigate hydrogen sulfide emissions is an effective approach. The reaction of sodium carbonate with hydrogen sulfide produces sodium sulfide, water, and carbon dioxide, helping to reduce hazardous off-gassing.

Step-by-step explanation:

The question deals with the mitigation of hazardous H2S gas generated from the decomposition of an expired NaHS solution. If the pH of the NaHS solution has decreased, it would indeed contribute to the release of more H2S gas, which is potentially very dangerous as it can reach immediately dangerous to life or health (IDLH) conditions.

Adding solid sodium carbonate to the solid NaHS in the tank could help neutralize the remaining acid, thus reducing the generation of H2S.

The sodium carbonate (Na2CO3) would react with any hydrogen sulfide (H2S) present to produce water (H2O), carbon dioxide (CO2), and sodium sulfide (Na2S), which is less volatile and therefore reduces the risk of off-gassing:

Na2CO3(s) + 2H2S(g) → 2Na2S(s) + CO2(g) + H2O(l)

This reaction should not pose any adverse effects if managed properly, with the correct stoichiometric proportions, under controlled conditions, and with adherence to safety protocols.