Details of a small aqua regia refinery setup

[4metals]

As I slowly come to the end of my working career, I have just completed a refining operation where they wanted to set up chemical stone removal and fire assay from scratch, including the fume scrubbing and vacuum system. I thought this would be a good opportunity to photograph the equipment and give our members some detailed descriptions of the equipment and some of the finer details of operation. So here goes!

Starting with the fire assay lab, this is the split parting hood. 5 feet of the hood is a parting hood for nitric acid parting of inquarted assay beads. The remaining 3 feet of the hood is for aqua regia digestions specifically for ICP work. In an effort to prevent the HCl fumes from aqua regia effecting the parting, the exhaust for the NOx reactions is drawn off the left side of the hood so the aqua regia fumes never have to pass over the parting side which is on the right.




The hood for the cupellations is a metal hood with a heavy steel base table to support 2 vcella kiln furnaces. The exhaust passes through a bag house which the local environmental folks required because of the lead emission potential. The reason for 2 kilns is the larger kiln will handle more fusions or cupellations and the smaller kiln is for both smaller number of assays run and melting the undissolved metal from stone lots and fine gold from smaller stone lots.


The blue table to the right of the furnace hood is a down draft table specifically for mixing flux fusions for sweeps analysis. The down draft table also passes through the bag house. This facility has a large existing melting and incineration capacity, necessitating bullion fire assays and sweeps assays.


The exhaust for the assay furnaces and the down draft table is provided by the bag house.



to be continued..........

 

[4metals]

Fume scrubbing

The chemical fumes are serviced by a 625CFM fume scrubber to treat the NOx emissions, Each of the 2 hoods, which will be seen in the next post, has a series of drops to remove the emissions from the aqua regia reactions through the scrubber. The hoods also have a series of vacuum valves to tie into the vacuum generator to facilitate filtration and solution transfer. This photo is the scrubber installed. Followed by the scrubber assembled at the fabricators shop.

This is the vacuum generator installed alongside the scrubber and the vacuum generator at the fabricators shop.


The fume scrubber is a modular unit which contains up to 4 scrubbing sections, each capable of handling a 250 CFM flow rate. This unit has 2 full 250 CFM stacks and a half stack handling 125 CFM. By changing the flow rate of the scrubber liquid and the CFM of the blower, the capacity of the scrubber assembly can be increased without purchasing an entire new scrubber.

 

[4metals]

The refining hoods

This setup has 2 hoods, each 8' long. As mentioned earlier each has a vacuum manifold and a manifold of scrubbed emission drops. This is the hood as it was first set up.
If you notice, the hood on the left has about 1/4 of the base cabinet missing and a hydraulic lift cart under the overhang. If you look closely you can see a round circle on the floor of the hood, this is the cover for "the hole". I have always been wary of accidents in a refinery so I have installed a hole which has a cover in case you need to use that hood space but normally this hole is made to accommodate raising and lowering filtration setups so when you pour acid into a filter it is done at a safe height. Hopefully the following photo's will demonstrate.





A plastic cement mixing tray is placed on the platform of the lift cart to serve as a spill catch, in case you miss. The receiver vessel with the vacuum port goes into the hole with the vac hose attached and the cart is raised to accommodate putting the filter into place. Once the filter is set and ready to use the suction is turned on and the cart is lowered into a comfortable and safe height to pour your acids. Once the job is filtered, the cart is raised to disassemble the filter and raise the full vessel to table top height for ease lifting to remove the vessel and proceed to the next step. If you notice, the "hole" has a raised lip to maintain the containment for spills of the interior of the hood. This hole accommodates 5 gallon vac jugs and 32 CM Buchner funnels.

 

[4metals]

Acid on Tap

The hood on the right is equipped with 2 shelves to hold 5 gallon vacuum jugs with teflon dispensing valves to hold nitric and hydrochloric acid. The jugs are piped into drums of acid to use vacuum to suck out the acid and fill the reservoir as needed. Each drum has a vacuum trap which contains a small moat of water to contain any fumes when the drum is sitting in the shop and if the vacuum gets too strong the trap will burp to allow air into the drum to prevent collapse. This is what the mechanism to feed from the drums looks like in the hood.


Once the vacuum valve is opened the vacuum is vented because the tee with the hole in it prevents vacuum from building up in the jug. By simply placing a finger over the "thumb valve" the vacuum builds and the reservoir fills up. The use of the "thumb valve" means you cannot walk away as acid fills the jug because when you remove your finger from the hole the vacuum is lost and flow stops.
View attachment acid on tap 1.mp4

 

[4metals]

The original concept when setting up this refinery was to process stone lots typically 50 oz or less. But that quickly proved to be inadequate. Fortunately the "hole" is just the right size for a 22 liter heated and condensed reactor which can process 100 ounce lots. This is the "hole" used for the 22 liter reactor.



The condenser feeds directly into the pickup for the fume scrubber. This series of photo's shows removing the reactor and sucking out the liquid by vacuum.




Now that I have seen the value of both making pouring operations safer and accommodating a 22 liter reactor for reactions, I regret not having a hole on each end!

 

[Yggdrasil]

As I slowly come to the end of my working career, I have just completed a refining operation where they wanted to set up chemical stone removal and fire assay from scratch, including the fume scrubbing and vacuum system. I thought this would be a good opportunity to photograph the equipment and give our members some detailed descriptions of the equipment and some of the finer details of operation. So here goes!

Starting with the fire assay lab, this is the split parting hood. 5 feet of the hood is a parting hood for nitric acid parting of inquarted assay beads. The remaining 3 feet of the hood is for aqua regia digestions specifically for ICP work. In an effort to prevent the HCl fumes from aqua regia effecting the parting, the exhaust for the NOx reactions is drawn off the left side of the hood so the aqua regia fumes never have to pass over the parting side which is on the right.
View attachment 63242
View attachment 63243
View attachment 63244

The hood for the cupellations is a metal hood with a heavy steel base table to support 2 vcella kiln furnaces. The exhaust passes through a bag house which the local environmental folks required because of the lead emission potential. The reason for 2 kilns is the larger kiln will handle more fusions or cupellations and the smaller kiln is for both smaller number of assays run and melting the undissolved metal from stone lots and fine gold from smaller stone lots.
View attachment 63245

The blue table to the right of the furnace hood is a down draft table specifically for mixing flux fusions for sweeps analysis. The down draft table also passes through the bag house. This facility has a large existing melting and incineration capacity, necessitating bullion fire assays and sweeps assays.
View attachment 63250
View attachment 63247
The exhaust for the assay furnaces and the down draft table is provided by the bag house.
View attachment 63248
View attachment 63249

to be continued..........

Thanks for showing us this.
The heater in picture one puzzles me though, what is the purpose on the contraption under it?
Or is it a complete assembly where the top and bottom is a part of each other?

 

[4metals]

They were in the very early stages of production when I was there to teach them some methods. The hot plate in the first picture is actually 2 hot plates. The larger one on the bottom is a 208 volt heater and there has yet to be an outlet for it. So the hot plate griddle was placed on top because there is a 110v outlet.

 

[anachronism]

I like the "hole" idea. Using large filters is cumbersome and that makes a lot of sense. How do you do the airflow calculations for when it is in use, as it's obviously leaving a much larger opening and changing the aerodynamics?

 

[anachronism]

Also what's the thick looking vacuum flexi hose that looks like it self seals and doesn't need clips please?

 

[4metals]

I like the "hole" idea. Using large filters is cumbersome and that makes a lot of sense. How do you do the airflow calculations for when it is in use, as it's obviously leaving a much larger opening and changing the aerodynamics?

When we set up the CFM for the hoods we base the flow on the full front opening of the hood. When in operation the plexiglass flaps fold down to protect the operators eyes and effectively reduce the opening by 1/3. So the flaps down when operating makes up for the “hole”.

 

[4metals]

Also what's the thick looking vacuum flexi hose that looks like it self seals and doesn't need clips please?

That is thick walled gum rubber vacuum hose with an abrasion resistant coating (actually fire hose fabric). I have been using this hose for suction for 30 years. It is quite flexible and never collapses under vacuum.
Vacuum Hose, Soft, 1/2" ID, 1-1/8" OD, Opaque Beige

https://www.mcmaster.com/5543K48

 

[BGDOCK]

I have to get my act together , seems like a really fantastic set up .

 

[4metals]

The moderators would like to thank all of the members who contributed to the original thread that this post was based on, as well as those who asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above, consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Details of a small aqua regia refinery. HERE

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