Q: What is an APT Elu-X?
A: APT’s Elu-X is a carbon elution system that compliments other APT processes, such as the APT TriTank Carbon In Leach or CIP systems. These systems are continuous in that ore is fed into the CIL continuously, but the loaded carbon is harvested once a day. The loaded carbon is then treated in batches and then discharged before being fed back into the CIL or CIP.
Q: What is an Elu-X used for?
A: The Elu-X is used to remove the gold from activated carbon which has been loaded with the gold in a cyanidation system like CIP or CIL. So first the gold is dissolved in the cyanide slurry, then it is adsorbed onto the activated carbon and the final stage is getting the gold off the activated carbon. That is called elution.
Q: How does elution work?
A: The carbon with the gold adsorbed on it is placed into a vessel called an elution column. A solution of hot sodium hydroxide and cyanide in water is then pumped through the carbon in the column and as it rises through the column, it dissolves or de-sorbes some of the gold. The solution, now with the gold dissolved in it, then passes through an electrowinning cell. An electric current is applied to the cell between the anode and the cathode which causes the gold to plate out onto the cathode. The solution, now with the gold removed, is reheated between being pumped through the column to dissolve off more gold. The whole process is continued for about two days by which time the gold has been removed from the carbon and deposited onto the cathode. The final step is to remove the cathode, which is normally made from steel wool, and dissolve it in acid to give gold sludge. This is then dried and smelted with borax to get the gold bullion. The carbon, now stripped of the gold, is returned to the CIL system to load more gold from the slurry.
The spent cyanide and sodium hydroxide solution will still have a little gold in it and also some value due to the cyanide and alkalinity value. It is therefore fed back into the first sector or tank of the CIL train.
Q: Can elution be used to recover any other metals like silver and copper?
A: No, elution as applied in the APT Elu-X is for gold only.
Q: Are there different types of elution systems?
A: Yes, the three most common ones are Atmospheric or Open Zadra, Pressurised or Closed Zadra and AARL. The Pressurised Zadra is the fastest, but being at high temperatures and pressure it is more sophisticated and also more dangerous if there was a leak. The pressurized Zadra system typically takes one day to complete a cycle. Open Zadra is what is used in the APT Elu-X and although slower, taking typically two days to complete a cycle, it is less sophisticated, easier to use and less dangerous.
Q: Does the spent carbon need need any further treatment before being put back into the CIL tanks?
A: If your ore or your process requires a lot of lime, then it is useful to acid wash the carbon to get this off before putting the carbon back into the leach train. To do this, the carbon is dipped into a solution of about 5% hydrochloric acid and left there until the effervescent reaction stops. Alternatively the carbon can be placed into an acid washing column and the dilute acid then pumped into the column to cover it. The process normally only takes less than an hour. *CAUTION – mixing acid with cyanide produces a lethal gas. The carbon must therefore be thoroughly washed with water to remove all cyanide before it is contacted with acid. The wash water should be placed back into the CIL train. After acid washing the carbon must again be thoroughly washed with water to remove the acid, but this time the acidic wash water needs to be neutralized with sodium hydroxide to pH 8 before being discarded.
When the carbon activity, or its ability to adsorb gold falls to a low level it needs to be thermally re-activated or regenerated. This happens in a carbon regen kiln that is a separate supply item and process. The carbon to be regenerated must be acid washed first. Because regen kilns are expensive and only need to be used periodically, most smaller operators will outsource this service to a custom regen centre.
Q: What sort of capacities do Elu-X systems come in?
A: The smallest is the Elu-X270, it has a capacity of 270kg of carbon and is used for cyanidation systems treating up to 3 tonnes of ore per hour.
Then comes the Elu-X540, with a capacity of 540kg of carbon and used for cyanidation systems treating up to 6 tonnes of ore per hour.
Then Elu-X750 for cyanidation systems treating up to 10 tonnes of ore per hour.
Finally the Elu-X1500 with a capacity of 1500kg of carbon suitable for cyanidation systems treating up to 20 tonnes of ore per hour.
Beyond that APT recommends more sophisticated Pressurised Zadra systems which are sourced outhouse.
Q: Do I need special skills to operate APT’s Elu-X?
A: The system is fairly simple and the manual can be used to guide you, but because it is a cyanidation system it is potentially dangerous if not operated properly. Also, each batch of carbon contains high gold value and incorrect operation could lose some gold. Therefore only persons with experience in operation elution systems and preferably qualified in cyanidation systems should operate the Elu-X.