Nitric acid (HNO) greatly enhance the rate of reaction. Although chromium (Cr), iron (Fe), and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal-oxide layer that protects the bulk of the metal from further oxidation. The formation of this protective layer is called passivation. Typical passivation concentrations range from 20% to 50% by volume (see ASTM A967-05). Metals that are passivated by concentrated nitric acid are iron, cobalt, chromium, nickel, and aluminium. Being a powerful oxidizing acid, nitric acid reacts violently with many organic materials and the reactions may be explosive. The hydroxyl group will typically strip
Simultaneously extracted metals and Acid-volatile sulfide the amount of HS produced by the reaction can be calculated. A few important things should be noted about this reaction: Once the quantity (in moles) of AVS has been determined in this way, it is divided by the dry mass of the sediment to obtain the AVS concentration. In addition to the gravimetric method described here, other methods, such as colorimetry, may be used. As noted above, treating metals-containing sediments with HCl liberates metal ions into the acid solution that were previously bound up with AVS. After treatment these are present in solution, along with any metals that were