Heating nitric acid passivation solution

First of two simultaneous responses --

A. You will need a good quality heater intended to live in nitric acid for a reasonable time. I would suggest a derated or even a double derated heater if you can stand the loss of tank space. It costs more to start, but will last a long time relative to a straight heater.

You will need a good, well designed exhaust hood that includes a fume scrubber, preferably with a neutralization solution.

Second of two simultaneous responses --

A. Ed,

There are no special problems to consider when heating a nitric acid solution. I use an immersion heater with an stainless steel element to heat a 200 gallon tank of 30% nitric to 120-140 °F. Good ventilation is necessary as well as a cover to prevent evaporation. The fumes are very corrosive. Hot acid is more dangerous than ambient temperature acid but both should be handled with great care. I would recommend a respirator, goggles ⇦ this on eBay or Amazon [affil links] , shoulder length gloves, face shield ⇦ this on eBay or Amazon [affil links] , goggles or acid suit. You didn't mention the volume you need to heat but the hazards increase when you have large open tanks. If you are going for a one-time deal and a relatively small volume, you will probably be ok. Any setup that will be used for an extended period would need some planning and most likely require you to employ a company that specializes in ventilation systems. Others options for small setups: immerse a smaller container in a larger one and circulate hot water around the smaller vessel, or heat the water for the solution first and then add the acid and allow the temp to fall (one shot deal though).

A. There are several alternatives such as teflon or exotic metal heaters that could be used. But, you could also heat it indirectly, that is through a double wall tank and hot water. Are you going to mix your nitric after it's heated? If so, you should investigate for possible exothermic reactions depending on your mixture.

A. Quartz heaters are a bad idea in any tank. They are expensive, easily broken and can present an electrical hazard when they do so.
Most passivation tanks I have seen are stainless steel.
A very popular solution to the heating problem is clamp on external heaters. They do not have to be chemical, or even water, resistant and are consequently cheap. They are also outside the tank, increasing working space and they can be changed without exposing the maintenance guy to chemicals.
A lid on the tank to keep it clean is good but at these concentrations and temperatures fume is not usually considered a problem. Monitor it and install fume extraction if it is necessary or save a lot of money and maintenance if it is not. Note: this applies to passivation only; electropolish and pickle tanks almost always need extraction.