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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Automatic solution temperature control and column back pressure control are the minimum automation required. Pfocess are numerous variations to, and combinations of, the basic processes as illustrated by the following:.
When the curve flattens out, the rinsing is sufficient even if the pH is only 4. 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.
Selection of design and operating flows is made on the basis of equipment costs and time constraints. Each method has advantages and disadvantages, which should be evaluated when deciding which process to use.
In this case a two compartment column is used. The circuit shown in Figure 4 has the following advantages over that shown in Figure 3 and may become the preferred process.
Part 3 outlines in full detail every action required on the part of goldroom personnel in order to operate the plant successfully. The gold depleted solution proceds then reheated and recycled to the carbon bed for reuse see Figure 1. Heat is transferred to this solution as it passes through the heat exchanger from thermocal which is being recirculated through a heater and the heat exchanger. High temperature limits are generally constrained by pressure and temperature limitations of system components, such as vessel design pressures elutin gasket temperature peocess.
The process is still widely used today because of its simplicity. Within a few hours, the alcohol is concentrated in the overhead condenser tank. As the solution flows through the electrowinning cell, gold is plated on to the steel wool cathodes. A comparison of the increase in stripping rate with temperature is shown in Figure 3. The AARL process should definitely be considered for large projects with sophisticated operators.
Heat exchanger pressure in ……. The advantages of this are dubious in that there would be more than enough time in a twenty four hour period for both steps to be completed in one column. The solution then flows up through the bed of carbon and overflows near the top of the stripping vessel. Several different alcohols were investigated.
These samples should be analysed for Ca plus Mg and then the totals plotted versus time. The solution pH is increased to 12 by the addition prkcess sodium hydroxide and electrowinning is started.
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By this time most of the gold and silver on the carbon will have been desorbed into solution and both the carbon and the solution will have reached an optimum temperature for the subsequent elution proper. The Micron process produces a very concentrated eluant free of alcohol, with gold and silver values eluton or three times higher than those in the loaded carbon.
Additional water is forced into this line via valve AV and the carbon is forced along the line through valve AV into the elution column. Plant practice generally indicates that about deg-F is the upper limit for maximum stripping efficiency. Loose copies are available. Carbon feed grades have varied between and ppm with corresponding final eluate as high as ppm gold but averaging nearer ppm.
It is much less expensive ;rocess operate and it produces a cleaner stripped carbon. The advantage to downflow is reduced potential for binding of flow distribution screens by tramp material in the carbon. As the carbon and preconditioning solution move into the lower section of eluhion column the hot water eluate passing up the column elutes the gold from the carbon and flushes out the preconditioning solution to become the final eluate.
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. Solution is circulated through electrowinning and back to the pregnant solution tank until acceptable barren levels are achieved.
After the desorption vessel has been filled with loaded carbon and solution flow is started, the only operator attention required is periodic system checks typical of any process plant operation. Ethanol and methanol were found to perform almost equally, but were substantially better that Isopropanol. After reagent addition, valve AV closes and the elution water pump recirculates the solution in the column 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 unit is then switched to the batch distillation mode. It then flows back into the eluate tank. flution
AARL Carbon Stripping System Operation: Elution & Electrowinning
The micron eluted carbon also appears to have a somewhat higher level of activity than carbon eluted by other methods. A falling top of column temperature is the best indicator of possible trouble caused by such things as dirty heat exchanger plates, thermocal heater not operating properly or pegged elutioj screens.
High levels of gold in recycled eluant result in a reduction in stripping rate as illustrated typically by Figure 2 3. The downflowingcondensate washes the gold values from the carbon particles into the boiler section below.
The reagent addition can be controlled by altering either the pump speeds, i.
Carbon Stripping – Denver Mineral Engineers
Details of the step by step sequence controller operation for the entire stripping process are outlined in part 2. Altering of the pump speed is preferable in cases where a change in the level of one reagent only is desired on a permanent basis. Ethylene or propylene glycol are frequently used, rather than alcohol, to increase the speed of atmospheric pressure Zadra stripping 7.
The elution step may be further divided into two major stages; carbon preheat and elution proper. In any case the procses water system here does not cater for the elutiom of both steps at the same time. 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.
Eluhion major elutioj include:. The Ok Tedi plant was seldom operated under the design conditions listed above. The stripping of gold from loaded carbon here involves two basic steps; Acid Washing and Elution. To alleviate this problem, most operations routinely bleed a fraction of their strip liquor inventory and replenish with fresh solution. Bottom of column pressure ……… around kPa.
The solution is then drained from the carbon until free of excess moisture.