Precipitate formed that melts at ambient temperature

Hi all

Quick question in case anyone can provide some insight regarding the following:

We have a tank located on surface level with ambient temperature approx. 90 degF. In this tank, we normally neutralize acid. The acid consists of Hydrochloric Acid + Corrosion Inhibitor + some degree of dissolved iron (acid is used to clean rust inside of carbon steel pipe). Once the acid is collected in the tank, it is then neutralized using a liquid solution of Soda Ash.

The tank is pumped out, but you do have remnant neutralized acid solution remaining in the tank as dead volume. Additionally, at points, calcium chloride brine and/or seawater may be added and pumped out from the tank. This means there is the pontential for all fluids to have some degree of contact with each other.

Recently, we found one of our valves "caked" with a hard crystalline precipitate. Colour is clear to light brown. No odour. A hammer and crowbar were used to break the crystalline structure from around the valve insert. It broke away like ice, but please note the crystalline precipitate was not cold (was ambient temperature). It was placed in the back of a truck bed and after appros. 15-20 mins, when we returned, the precipitate had melted (no trace of solids seen). All that was left was a water-like substance on the truck bed which was basically colourless and odourless. No external heat was added other than probably that from sunlight.

Any help or insight as to what precipitate it was would be much appreciated. I do thank you for your time and assistance with this. Feel free to message me at [email protected] with responses also.

Rgds
Al