Use of oxidizers

[nickvc]

Having watched quite a lot of YouTube videos over the last few weeks one thing seems to stand out to me.
Many of the videos show the maker adding HCl to their scrap and then slowly adding the oxidizer , which is the way we advise , but after an addition of their chosen oxidizer and there’s no reaction they assume the dissolution is complete but they never add a little more HCl to check whether that’s the missing ingredient , the point I’m trying to make is that the HCl will decompose/ dissipate especially if hot fairly quickly so adding more oxidizer will not reactivate the solution , adding a little HCl will cause no problems with precipitation unlike the oxidizers so always finish your processes with a dash of HCl and watch for any reaction..

 

[4metals]

Excellent observation, one way around this is to use Hydrochloric Acid at it's azeotrope strength which is about 20%. Because concentrated reagent at 36% boils off so easily and quickly reduces the available Hydrochloric Acid which can put you in the situation Nick is describing. If you simply cut your Hydrochloric Acid in half with water and double the quantity it will not volatilize away so quickly. The down side to this is excessive waste volume.

Home hobby refiners I would encourage Nick's solution, possibly in a condensed reactor to eliminate the volatilizing of Hydrochloric Acid. Commercial refiners with waste treatment often choose to dilute.

 

[orvi]

You always want to minimize vapor losses of HCL as it is not only wasteful money-wise, but also it wrecks your equipment/ducting/fan/hood more. I use 30-32 % tech grade acid, and my aim with say AR is to shoot the oxidant for the first addition to kickstart the rolling reaction, but never exceed 75-80 °C - as 30% HCl emit significant gas HCl at temps over this. After around 1/3 of the material is consumed, so is the 1/3 of the HCl. And you are at that 20 % sweet spot and then you can heat it as you wish, loss of HCl is minimal