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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In general atmospheric pressure Zadra stripping is favored for smaller projects where the increased size of equipment can be justified by a simplification of the system.
This could be excessive and wasting potable water. The reagent addition can be controlled by altering either the pump speeds, i. The carbon is then steam stripped to leution residual alcohol. It is much less expensive to operate and it produces a cleaner stripped carbon.
Prcess Ok Tedi plant see Figure 2 differed from the pilot plant in a number of significant ways, elutjon main one being the carbon feed system which comprised two sets of transfer tanks and vessels which were alternately filled with carbon and the vessels pressurised with hot final eluate to drive the carbon into the column. The barren solution is then pumped out of the eluate tank into the process water tank.
This had two advantages, firstly it allowed fast on line adjustment of the composition of the barren eluate based on free NaCN in the final eluate, and secondly it minimised provess problem of fouling of the barren eluate heater. Thermocal temperature in ………. This offers the potential of either designing for multiple stripping cycles each day and reducing equipment sizes in new plant design, or increasing daily capacity in existing mills by stripping on additional shifts each day.
This is due to its significant cost advantage over atmospheric pressure Zadra systems. After rinsing the carbon is pressure transferred to the elution column. The downflowingcondensate elutionn the gold values from the carbon particles into the boiler section below.
The main disadvantage of the original Zadra process is its low rate of desorption. Potable water then continues to flow through the system as per the elution stage procezs another twenty minutes, this taking some of the heat out of the carbon and the thermocal.
The last aal volume of eluant water is generally introduced at ambient temperature to cool the carbon for transfer out of the column. Each method has advantages and disadvantages, which should be evaluated when deciding which process to use. Pressure stripping columns are normally sized with a height to diameter ratio of about 4 to 1. Details of the step by step sequence controller operation for the entire stripping process are outlined in part 2.
As the solution flows through the electrowinning cell, gold is plated on to the steel wool cathodes. Fluctuations in flow and temperatures can reduce stripping efficiency but the only adverse effect is an extension of the required stripping cycle time. In any case the potable water system here does not cater for the running of both steps at the same time.
Barren strip solution is typically pumped through a heat recovery heat exchanger and a solution heater. The process involves a series of procedures generally starting with an acid wash followed by a water wash to remove residual acid.
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Plant practice generally indicates that about deg-F is the upper limit for maximum stripping efficiency. High pressure operation is accomplished by means of a high pressure solution pump and a stripping column pressure control regulator. High temperature limits are generally constrained by pressure and temperature limitations of system components, such as vessel design pressures and gasket temperature limits. The eluiton solution is drained from aark carbon bed and an alcohol solution is added to the vessel.
AARL Carbon Stripping System Operation: Elution & Electrowinning
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 inline screens.
The tower bottoms solution is then free of alcohol and loaded with gold solution which has been stripped by the refluxing action in the column. With the AARL process, elution is normally proceeded by acid washing the carbon. The AARL process should definitely be considered for large projects with sophisticated operators.
There are, however, isolated examples of operations using methanol. Acetonitrile may be substituted for the alcohol, but its higher cost generally discourages its use.
The process generally takes about 48 to 72 hours.
Barren solution is then returned to the barren solution tank for recycle see Figure 4. At the end of the elution stage the thermocal heater elutin and an additional amount of NaOH is pumped into the eluate tank via valve AVthis bringing the pH of the eluate solution up to the desired level. Above deg-F cyanide was decomposed and aaarl gold precipitated in the carbon.
The condensate recycle spray is stopped and the alcohol is allowed to boil out of the pregnant solution. Operation at deg-F requires operating pressures of 10 to 15 PSIG to prevent flashing steam in the system.
Carbon Stripping – Denver Mineral Engineers
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. The Micron method involves pretreatment pricess loaded carbon, with a caustic cyanide solution followed by elution with an alcohol mixture.
The micron eluted carbon also appears to have a somewhat higher level of activity than carbon eluted by other methods.
The pregnant liquor is then drained from the desorption vessel. The solution is cooled by exchanging heat with barren solution and flows through a back pressure control valve, to the pregnant solution holding tank. Procese circuit shown in Figure 4 has the following advantages over that shown in Figure 3 and may become the preferred process.