AARL process as applied at SDGM. • Identify the key elution circuit components. • Demonstrate an understanding of carbon reactivation theory. • Demonstrate an. Request PDF on ResearchGate | Modelling of the AARL elution process | The influence of temperature on the equilibrium adsorption of gold and hydroxide ion . successful methods is the carbon-in-pulp (CIP) process. In CIP processing elution rig was commissioned to simulate industrial Zadra and AARL carbon elution.
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It was not, however, until methods for chemically desorbing gold from loaded carbon were developed, that the process came into widespread use for gold recovery from ore. The major processes include: Most columns are operated with upflow of solution, but some plants have selected to elute by downflow. Control of the amount of solution purged from the system is done either on a routine scheduled basis or by monitoring stripping efficiency and bleeding as efficiency drops. Displaced water flows out of that column through the inline filter, via valve AV into the potable water tank.
To alleviate this problem, most operations routinely bleed a fraction of their strip liquor inventory and replenish with fresh solution. Top of column temperature ………. Operating temperature limits of deg-F procses widely specified because of temperature limitations of the butyl rubber lining material utilized to line the strip vessel.
This information is displayed on the control cubicle. We have a metallurgical test for every possible mineral type and treatment.
In any case the potable water system here does not cater for the running of both steps at the same time. Continued research at the USBM revealed that the Zadra process stripping rate could be increased greatly by stripping at higher temperatures 4.
Gold is recovered from the pregnant eluant by electrowinning and the barren eluant is discarded See Figure 3. When desorption is completed, as indicated by gold solution concentration reaching a constant level in the column boiler, alcohol recovery commences. Disadvantages of the AARL process include the requirement for high quality water, high water consumption, the potential elutoin mixing acid with cyanide, and the necessity for automated controls.
During eluton elution cyclewater is drawn from the potable water tank and pumped through the heat exchanger via valve AV into the column.
The startup and operation at Ok Tedi are discussed in some detail in the Reference A. The high solution grades make recovery methods such as chemical precipitation and aluminum foil electro-deposition very attractive. The reagent addition can be controlled by altering either the pump speeds, i.
The process generally takes about 48 to 72 hours.
AARL Carbon Stripping System Operation: Elution & Electrowinning
By this time most of the gold will have been liberated from the carbon back into solution form. The major processes include:. It is much less expensive to operate and it produces a cleaner stripped carbon. The Ok Tedi plant was seldom operated under the design conditions listed above.
The solution pH is increased to 12 by the addition of sodium hydroxide and electrowinning is started. After reagent addition, valve AV closes and the elution water pump recirculates the solution in the elktion by pumping it via the heat exchanger and valve AV up through the column and out through valve AV back to the water pump.
The quality of water used has a substantial effect on stripping efficiency with the AARL procedure. Ethanol is generally used rather than methanol. The advantage to downflow is reduced potential for binding of flow distribution screens by tramp material in the carbon. The following calculated results were obtained from the computer simulation of the elution column using Ok Tedi plant design data.
The entire stripping cycle takes about 8 hours. Internal solution distributors and collectors are used to provide even flow of solution throughout the carbon bed. Solution bleeding is required to prevent the buildup of contaminants, which reduce stripping efficiency. Today, many options are available to the recovery plant designer and operator for the stripping of gold from carbon.
In general atmospheric pressure Zadra stripping is favored for smaller projects where processs increased size of equipment can be justified by a simplification of the system. Should any difficulties occur eljtion the stripping process, possible faults with remedial action have been detailed in part 4 of this manual.
Methanol, ethanol, and Isopropanol were all found to increase the gold desorption rate. This idea was discarded in practice, in favor of the simpler one step caustic cyanide elution.
High levels of gold in recycled eluant result in a reduction in stripping rate as illustrated typically by Figure 2 3. The micron eluted carbon also appears to have a somewhat higher level of activity than carbon eluted by other methods. Based on the Pilot plant test results these columns would each have an eluting capacity of 60 tonnes of carbon per day. The solution then flows up through the bed of carbon and overflows near the top of the stripping vessel.
Barren strip solution is typically pumped through a heat recovery heat exchanger and a solution heater. This is due to its significant cost advantage over atmospheric pressure Zadra systems. This stage continues until five bed volumes of water have passed through the column 2.
Potable water then continues to flow through the system as per the elution stage for another twenty minutes, this taking some of the heat out of the carbon and the thermocal. The advantages and disadvantages of each procedure are discussed.