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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By L D Michaud T Most columns are operated with upflow of solution, but some plants have selected to elute by downflow. The gold depleted solution is then reheated and recycled to the carbon bed for reuse see Figure 1.
The AARL process should definitely be considered for large projects with sophisticated operators. The elution step may be further divided into two major stages; carbon preheat and elution proper. Loose copies are available. High pressure operation is accomplished by means of a high pressure solution pump and a stripping column pressure control regulator. Acid washing has been shown to typically increase the efficiency of AARL stripping.
AARL Carbon Stripping System Operation: Elution & Electrowinning
Au per ton of carbon. This can be confirmed by visual inspection at the pump or valve. Again do not risk flooding the kiln by over flushing the line.
Each method has advantages and disadvantages, which should be evaluated when deciding which process to use. The stripping efficiency is virtually independent of eluant water flow rate in the range of 1 to 5 bed volumes per hour. The Micron elution procedure takes advantage of the enhanced stripping rate achieved with alcohol, but confines the alcohol to the closed stripping unit.
Atmospheric pressure Zadra stripping was the first commercially successful process developed for stripping gold from carbon. Acetonitrile may be substituted for the alcohol, but its higher cost generally discourages its use.
Gold is elutoin from the pregnant eluant by electrowinning and the barren eluant is discarded See Figure 3. To determine the optimum time it is necessary to take samples every fifteen minutes from the rinse discharge line sampling point at the top of the acid wash column.
Methanol, ethanol, and Isopropanol were all found to increase the gold desorption elutikn.
Due to the timed cyclical nature of the procedure, a programmable logic controller PLCautomatic pump starting and automatic valves are generally used to time and sequence the system. After acid injection and soaking, water is pumped into the bottom of the column via valve AV and as it rises through the column to exit via valve AVit rinses out the acid. Denver Mineral Engineers, Inc. Many methods are used commercially for recovering gold and silver from loaded activated carbon.
It then flows back into the eluate tank. The mere following of the instructions given in that section will not ensure effective stripping results as there are many extraneous factors which need to be taken into account.
Carbon Stripping – Denver Mineral Engineers
Displaced water flows out of the top of the column through valve AV to the tailings hopper. At the end of the carbon cool stage, water is pumped into the column via valve AV so as to maintain pressure within it and force the barren carbon out of the column via valve AV into the carbon transfer line.
Changes in the duration of soaking time, for most carbons, has little effect on stripping efficiency. To operate at higher temperatures, the process must operate at pressures higher than the vapor pressure of the solution.
In practice the feed system to each column had a limit of 36 tonnes per day. Sodium cyanide is sometimes added to the solution but it is frequently unnecessary. When desorption is completed, as indicated by gold solution concentration reaching a eluhion level in the column boiler, alcohol recovery commences.
Selection of design and operating flows is made on the basis of equipment costs and time constraints. Changing of the dosing time in the stripping sequence step procews results in the changing of the levels of both NaCN and NaOH as the same timer controls both pumps.
In plant operation alcohol stripping normally requires about 12 to 16 hours to strip carbon to less than 3 oz. Electrowinning One bed volume thirty minutes after the commencement of the elution step 06 the electrowinning cell may be put into operation.
Buildup of miscellaneous ions in solution after continued recycling also reduces stripping efficiency.
AARL Carbon Stripping System Operation: Elution & Electrowinning
With the AARL process, elution is normally proceeded by acid washing the carbon. The following calculated results were obtained from the computer simulation of the elution column using Ok Tedi plant design data. The advantages and disadvantages of each procedure are discussed.
The solution then flows up through the bed of carbon and overflows near the top of the stripping vessel. The final eluate exits just below the top compartment as shown in Figure 5.
The main drawback to the alcohol stripping process is the potential for fires. The process was developed by J. The pregnant liquor is then drained from the desorption vessel.
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The majority of pressure strip vessels are constructed from stainless steel, but many carbon steel vessels are providing satisfactory service. One bed volume thirty minutes into the elution stage the eluate pump is started and pregnant solution from the eluate tank, is pumped up into the electrowinning cell on the first floor of the goldroom.
It is interesting to note that the Zadra stripping procedures researched by the USBM, originally envisioned presoaking carbon with a caustic cyanide solution followed by elution with deionized water. The major processes include:. As the solution flows through the electrowinning cell, gold is plated on to the steel wool cathodes.
After rinsing the carbon is pressure transferred to the elution column. Acid washing is used with all of the other stripping systems, but it is mentioned specifically with the AARL procedure, because AARL systems generally use the stripping vessel to acid wash and acid washing is, therefore, controlled as part of the stripping sequence.
Electrowinning of gold from the pregnant solution is done on a batch basis. Should any difficulties occur during the stripping process, possible faults with remedial action have been detailed in part 4 of this manual. Fluctuations in flow and temperatures can reduce stripping efficiency but the only adverse effect is an extension of the required stripping cycle time.