We performed a new refining operation and applied some of the recommendations mentioned in this forum.
Obviously we could not implement all the recommendations due to device problems (until they are fixed soon)
I try to explain the process step by step, with the changes applied in each step
We prepared a reliable feed with the following analysis:
Au:755.4
Ag:57.4
Cu:164
Zn:11.2
Fe:0.6
Ni:4.8
Cd:6.4
Feed weight 2859.8 gr. equivalent to 750 carat.
Melting and Flaking :
We melted all the scrap in one step (for the homogeneity of the percentage of silver in the gold beads), then we emptied the melt into water at 2 ° C and flake it well. Then we dried and weighed. 2.2 grams of gold was not obtained after smelting and flaking operations. I must say that we used boric acid before melting to cover the graphite crusible.
Scrap digestion , Gas purification with scrubbers:
According to the calculations, we should add 2.4 lit nitric acid and 9.8 lit hydrochloric acid.
First we added 8 liters of HCl and 1 liter of HNo3. After about an hour, we added another 1 liter of nitric. After one hour, we added 0.5 liters of HNo3 and 1.8 liters of HCl.
We did not use hydrogen peroxide in this reaction, but in the past we added it using a dosing pump.
After an hour of reaction, we turned on the Tumbler rotating.
The reaction subsided after about 4 hours and 30 minutes. The amount of undissolved seeds was 23.15 gr.
Scrubbers:
Fortunately, we have removed ammonia from the scrubbers. It was great.
We have four scrubber towers that pump water from two tanks to purify gases. We set the pH in the first tank to 10.5 with a dosing pump and a concentrated caustic soda solution. We also manually set the second tank of scrubbers to ph 10.5.
At the beginning of the reaction we had some fume at the end of the chimney, but by adjusting the airfan flow with driver, all the fumes was removed completely. When the airfan motor frequency was between 9 and 15, we had no odor or fumes in the chimney.
When the frequency was set above 25, we had some odor and steam at the end of the chimney.
When the frequency was less than 8, gas was released into the room.
We set the frequency at 18 at the peak of the reaction and 10 when the reaction calmed down.
Diluting, Cooling and Filtering AgCl:
After the reaction subsided, we added 3 liters of ice and allowed the solution to cool. We did not add extra water at this stage. (In the past we used to add water).
Unfortunately we could not modify the previous filters here. But we used a fabric filter and two paper filters to cover the gaps.
(In the case of gold filtration, we did better, we filtered with the italimpianti filter, I will explain later)
We filtered the solution and the silver chloride remained. We washed the Tumbler and valves completely.
Rinse the silver chloride with cold water until the soluble stannous chloride test is negative.
We have not removed the cylindrical filter yet, the stannous test was negative, the color of the filter was not gray, ie the silver chloride was filtered.
We also collected unresolved gold beads.
23,15 gr.
We wash the silver chloride filter and store it in gallons of chloride with some water.
DeNOxx:
(we could not heat the solution, so we could not use sulfamic acid)
After the clear golden green solution was transferred to the first tank, we added a little water. Then we slowly added the urea and stir it.
We added about 600 gr.of urea.
At first it was completely reactive and solvable. Finally, the urea seeds reached the bottom of the tank, so that it felt unresolved in the bottom of the tank. (But we still have doubts about the amount of urea seen by the reaction)
Precipitation:
We know the best precipitator is so2 gas, and the next option is smb. We prepared ourselves to use SMB, unfortunately we did not use it in this process for two reasons, first, our tanks do not have a chimney for 24-hour ventilation, our first tank does not have a mixer with shaft and propeller. After making the changes, we will definitely use smb.
Unfortunately we had to use hydrazine. But this time we used much less. We dissolved one liter of hydrazine in one liter of distilled water.
First, we added 500 cc to the solution and mixed it well. After a few minutes, we added another 500 cc and mixed well. We took a sample from the solution and performed a stannous test. The sample became completely dark. Then we added another 400 cc and mixed, even moving the settled gold particles. After 15 minutes and the particles settle. We tested the solution again, this time it darkened less but it was positive again. The color of the solution had changed from golden green to blue-green, but we were not sure. We added some precipitate again, it did not react when added, but reacted by stirring a small amount. We did the stannous test again, it was as dark as the previous test but like a semi-dark cloud, not black and purple.
(We have doubts about the diagnosis of Stanus chloride test. Because the sample is blue and green. When we add a drop of Stanus chloride, a semi-dark cloud forms after a few seconds, but the blue color is still visible)
Add a little flocculant, mix well and leave for 30 minutes.
Gold Filtering :
At this point we did not use incomplete filters. We applied the italimpianti filter according to the photo. We used two paper filters and closed the filter with a rubber band around it.
First we drained the salt solution of the base metals. When the gold sponge appeared, we started rinsing with hot pressed water in the tank. The gold sponge was drained slowly and hot water was passed over the gold several times. We kept the diaphragm pump on for about 30 minutes. The gold sponge dried a bit. (According to photo)
XRF Pure Gold:
We took some samples of gold sponge to test with Xrf .
The result of the analysis:
Au:998.8
Pt:1.1
Ag:0.0
Cu:0.0
(We did not have platinum in the initial feed analysis.)
Drying and melting:
This time we dried the gold sponge with tow induction furnace. Fill the tow graphite crucible , after drying, turn off the furnace, add again, turn on the furnace, dry , and so on.
We did not add any flux.
One of the crucible was new. Another used.
We performed several XRF tests after melting.
1) XRF sample of new crucible:
Au:999.4
Ag:0.6
2)XRF sample of used crucible:
Au:999.3
Ag:0.4
Cu:0.1
Fe:0.23
3) When I focused with XRF on the surface contaminated areas of the molten sample:
Au:968
Fe:29.6 !!!!!!
Cr: 1.9
W:4.9
Ru: 0.3
Zn:0.4
The discovery of iron surprised me. We did not dry the sponge with a steel container. Pure gold contact before melting was only with a steel spoon to fill the crucible.
Is iron used in the production of graphite crucible?
We melted the gold again with some silver, to the 999 carat. A very small amount of impurity was observed on the molten surface during melting. It was shiny but not perfect. When draining the melt, add as much pinch of potassium nitrate and borax.
Accounting:
Total gold obtained without gold trapped in silver chloride and soluble cement:
Finally we have 2122.65 gr (999)
We have undissolved 23.15 gr (755)
Gold recovered : 2850.67 gr (750)
Starting weight : 2859.8 gr (750)
Gold Not obtained: 9.13
Yield without AgCl and cementation:99.68
Cementation:
We are preparing the second and third tanks for solution cementing with copper plates and air flow (according to 4metal recommendations). After finishing a few refining operations, we want to use them.
Before the hydroxide tank, we had two cylindrical tanks and two waste water tanks. We want to make cement with copper plates in the cylindrical tanks.
Also cement with atomize copper powder in tanks with mixers and air pipes.
We are equipping them.
Obviously, the cement report is completed after a few operations to increase the solution.
Our solution has not yet reached the filter press stage, but we have adjusted the pressure of the hydraulic filter jack until no liquid escapes.
We connected the filter press to the air for drying the hydroxides.
The waste water report will be completed.
