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 may also be preferred for areas where extreme ease of maintenance and operability are a priority due to a lack of skilled manpower. During the elution cyclewater is drawn from the potable water tank and pumped through the heat exchanger via valve AV into the eluution.
Solution bleeding is required to prevent the buildup of contaminants, which reduce stripping efficiency. Continued research at the USBM revealed that the Zadra process stripping rate could be increased greatly by stripping at higher temperatures 4.
Likewise it should be remembered that the controllers will not operate if a local stop switch is depressed. The quality of water used has a substantial effect on stripping efficiency with the AARL procedure. This pump would replace the transfer vessels in the Ok Tedi design and could be located near the top of the column using the configuration shown in Figure 3 or near the bottom of the column if used with a eluate transfer pump as shown in Figure 4.
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The sequence controller time for step 06 should then be reset to the time indicated by the graph. Alcohol stripping has generally fallen out of favor due to the flammability concerns. Acid washing is used with all of the other stripping elutlon, 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.
The last bed elutioh of eluant water is generally introduced at ambient temperature to cool the carbon for transfer out of the column. Electrowinning of gold from the pregnant solution is done on a batch basis. The process is still widely used today because of its simplicity.
The advantages and disadvantages of each procedure are discussed. Details of the step by step sequence controller operation for the entire stripping process are outlined in part 2. The presoak solution is drained from the carbon bed and an alcohol solution is added to the vessel.
This necessitates larger carbon inventories and larger equipment than other faster processes. High temperature limits are generally constrained by pressure and temperature limitations of system components, such as vessel design pressures and gasket temperature limits. The design solution flow rate is generally based on a compromise between reduced elution time and increased equipment costs at higher flow rates. Several different alcohols were investigated.
The implementation of a hot acid wash step has been shown to reduce water quality requirements to a certain degree. 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. It is however very reliant upon the availability of an abundant supply of good quality water and its water usage is far greater than that of either the Zadra system or the more recently developed solvent stripping system.
Internal solution distributors and collectors are used to provide even flow of solution throughout the carbon bed. The loaded carbon and hot preconditioning solution move down the top section of the column together.
Glycol stripping frequently is used to increase capacity in existing Zadra operations, but economics usually favor conversion to pressure stripping if continuing operation is planned.
The circuit shown in Figure 4 has the following advantages over that shown in Figure 3 and proceas become the preferred process. The stripping of gold from loaded carbon here involves two basic steps; Acid Washing and Elution.
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 Micron elution procedure takes advantage of the enhanced stripping rate achieved with alcohol, but confines the alcohol to the closed stripping unit. Ethylene or propylene glycol are frequently used, rather than alcohol, to increase the speed of atmospheric pressure Zadra stripping 7.
The Micron method involves pretreatment of loaded carbon, with a caustic cyanide solution followed by elution with an alcohol mixture. Changing of the dosing time in the stripping sequence step 02 results in the changing of the levels of both NaCN and NaOH as the same timer controls both pumps. The following calculated results were obtained from the computer simulation of the elution column using Ok Tedi plant design data.
The elution step may be further divided into two major stages; carbon preheat and elution proper. The stripping efficiency is virtually independent of eluant water flow rate in the range of 1 to 5 bed volumes per hour. This is in direct contrast with the Zadra and AARL procedures, which produce eluant concentrations one or two orders of magnitude lower.
AARL Carbon Stripping System Operation: Elution & Electrowinning
Gold ExtractionGold Refining Tags: After stopping the elution water pump locally, reset the switch and then reset the sequence controller by: Each column was mm diameter by 10 metres high which for 24 tonnes per day of carbon per column was equivalent to the pilot plant operating at 1 tonne per day. The process generally takes about 48 to 72 hours. Disadvantages of the AARL process include the requirement for high quality water, high water consumption, the potential for mixing acid with cyanide, and the necessity for automated controls.
The efficiency of the electrowinning cells is also procfss to stripping efficiency. The major processes include:.
Carbon Stripping – Denver Mineral Engineers
Upflow operation means that the carbon bed is always flooded, and insures that the carbon is continually contacted by strip solution. This stage continues until five bed volumes of water have passed through the column 2. By this time most of the gold will have been liberated from the carbon back into solution form. Gold is recovered from the pregnant strip solution by electrowinning onto steel wool. This prrocess reduce the proceas to reactivate carbon as frequently at some operations.
Automatic solution temperature control and column back pressure control are the minimum automation required. The acid rinse step 05 is currently set for 2. Sodium cyanide is sometimes added to the solution but elutiom is frequently unnecessary. Ethanol and methanol were found to perform almost equally, but were substantially better that Isopropanol.
Within a few hours, the alcohol is concentrated in the overhead condenser tank. Altering of the pump speed is preferable in cases where a change in the level ptocess one reagent only is desired on a permanent basis.