Sulfuric cell TRA setup: need your help!

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Martijn

Well-known member
Joined
Aug 3, 2014
Messages
2,468
Location
Netherlands, Zeeland
Gents, I need your input to write my final paper to become a certified safety advisor, and with it, contribute to the safety section of this great site.

My goal is make an assessment of the risks involved with the Sulfuric cell processs. It will be put in the safety section after completion.

I tried to put all the steps in order, with the help of the post on this site, mainly steve's great tutorials and comments, thanks again steve!
to get a complete picture, I would like you to fire away about anything relevant you can come up with. All info is welcome; from small insignificant things to the biggest hazards and epic fails encountered by our members.
I will check all risks we come up with against Dutch law and regulations, where I will be presenting the paper. I will incorporate the relevant items in the TRA for this forum.

Below my description of the process steps:
Gather materials like acid, glass oven dish, copper mesh and wire, lead for the cathode, power supply, capable of delivering sufficient voltage and amperage. (dependent on size of set-up.)
And some cleaned gilded material to strip. Plastic strainer and rinse water bucket, stripped material dump bucket.

Basic safety related items and measures:
Safe work place with fume hood, goggles or full face screen, acid resistant gloves and apron, spill container under process, MSDS of all chemicals used.

Preparation: make a copper basket, cast or make lead cathode, install fume hood, clean solder from gilded parts before stripping.

Set-up process:
place dish in spill container, put lead cathode in, connect leads and clamps, fill basket, pour in acid, lower basket in dish and turn on the power. set voltage limit to ....V and current limit to max.

During process:
Shake or stir the content of the basket when current drops to expose covered parts to acid.
monitor: foam build- up, black layer build-up on the bottom and electrical short-curcuits in acid.
Temperature should not go over ... degrees C?

When done:
turn off power supply, lift basket out acid and let drip out for some time.
empty contents of basket in strainer to spray-rinse, catch rinse water in bucket, and dupm the rinsed parts in a bucket.
Refill the basket, do not let the copper basket come in contact with water to prevent dilution of the acid or worse like exothermal reaction upon contact with water.
Repeat until you run out of stripped material, or the sludge makes the electrodes short-out.

Siphon off the clear acid for re-use, empty metal sludge with acid in container with water to dilute the acid to filter it with paper filter.

Dispose of waste and chemicals.
Store materials and chemicals.

After the risks are inventoried, they will be evaluated and categorized according a risk assessment matrix based on likelihood of occurrence and impact of an accident.
So the effect and likelihood of an accident is info I would also like some info about.
Control measures to prevent or reduce the risk to an acceptable level will be put in the TRA.

Please try to describe the accident or risk and what could be done to prevent it.
Also the effect of (near)accidents are very helpful.

I really don't expect to predict all the risks, so I need your input here. everything is open for debate, but the emphasis should be on the risks and control measures you can think of.
If someone should ever read the TRA, it would immediately highlite the risks and force one to think twice about rushing head first into something that can go irreversibly wrong.

Hope you will al jump on it!! Be safe, Martijn.
 
lower basket in dish and turn on the power. set voltage limit to ....V and current limit to max.
I would think both voltage and current will depend on the cell design, size of electrodes and amount of material. A voltage (maybe 2 - 5 V??) is required to initiate the current flowing across the cell, and it's that current which creates the persulfuric zone around the anode that does the stripping.

It is therefore the current that you would be better to regulate, if you can. If you have a variable lab power supply that can regulate in either voltage or current mode, choose current mode. You will find a large increase in current will cause only a small voltage rise. Alternatively for a variable constant voltage source, once you hit the voltage trigger level (something of a knee in the V/A curve), increasing the voltage a small amount over that level will cause a large increase in current.

Temperature should not go over ... degrees C?
The electrolyte heating is caused by the input power; Watts = Volts x Amps. But the greater the dissipation surface area, or other active cooling methods, the greater power you can supply without overheating. Opinions vary, but consensus is that 30 - 35°C is a reasonably conservative upper end for temperature.
 
I got a left over piece of roofing lead from at the local metal recycling company for one euro per kilo. I melted it in a stainless steel pan on the normal cooking furnace. (With the suction fan on, of course) Impurities and so (I believe oxides) will float to the top, I would try to keep these out of my cathode. I came across some very informative bullet casting video's for tips on how to pour lead. It melts at 327 degrees C or 621F. Keep your mold very dry, the lead tends to splatter up and over the edge if there's moist left in the mold. Mine was made with cement.
 
Jason, thanks for your reply. FYI: The TRA will be describing a 1 to 1,5 liter cell setup. The power supply is in my case a lab supply with independent V and I limit control to max. 24 Volt and 3 Ampere, I expect the voltage to be as low as a couple of volt, depending on the specific element potential of gold (electron volt) in this specific acid. To prevent impurities going into solution or the black powder I will be keeping the voltage as low as possible by experimenting with current. I will experiment with current limit to keep acid temperatures low.

Persulfuric zone you say?.. I've got some more reading to do.
 
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