There is a system called if I remember well Micron elution that use alcohol only, After the carbon is soaked in cyanide and caustic it is eluted by distilling ethanol trough  the carbon column and on the top there is a condenser that cool the alcohol to about 75deg C then the liquid percolates through the carbon again. the condensate flows into a bottom chamber where the gold is cumulating. At the end about 6 hours the alcohol is distilled off into a separate line and condensed into a tank leaving just an highly loaded aqueous solution of gold that can be placed in an electro wining cell and recovered as metal. These process is highly efficient and it also remove the organics that may be with the carbon.

I wouldn't use this in an atmospheric zadra system due to the danger of fire.

Yves 

ALCOHOL STRIPPING

Further research at the USBM showed that the atmospheric pressure Zadra stripping cycle can be made to operate much faster by the addition of alcohol to the strip solution (6).

Figure 6 shows the dramatic laboratory results obtained by adding 20% ethyl alcohol to a Zadra solution. Several different alcohols were investigated. Methanol, ethanol, and Isopropanol were all found to increase the gold desorption rate. Ethanol and methanol were found to perform almost equally, but were substantially better that Isopropanol.

In plant operation alcohol stripping normally requires about 12 to 16 hours to strip
carbon to less than 3 oz. Au per ton of carbon. This is achieved at flow rates in the
range of 2 bed volumes per hour operating in series flow with electrowinning cells.

The main drawback to the alcohol stripping process is the potential for fires. Fires
have been reported at several alcohol stripping operations. The electrowinning section is especially vulnerable to fires because of the potential for sparks.

Ethanol is generally used rather than methanol. This is due to ethanol’s greatly lower health risks from exposure to vapors. There are, however, isolated examples of operations using methanol.

Ethylene or propylene glycol are frequently used, rather than alcohol, to increase the speed of atmospheric pressure Zadra stripping (7). Typical strip times with glycol are 24 to 36 hours.

Glycols are generally used, rather than alcohols, because they are virtually
uninflammable. The disadvantages of glycols are their inferior strip rate increase and higher costs.

A typical glycol stripping solution contains 20 to 25 wt% ethylene or propylene glycol, and 2 wt% sodium hydroxide. Sodium cyanide is sometimes added to the solution but it is frequently unnecessary. The solution is heated to about 190 deg-F and pumped through the carbon stripping vessel at a flow rate of about 2 Bed Volumes per hour. Gold and silver values are recovered from the pregnant solution by electrowinning and the barren solution is reheated and recycled through the stripping vessel. Glycol consumption is typically in the range of 20 to 40 gallons, per ton of carbon stripped.

MICRON STRIPPING

The most recently developed stripping procedure being used commercially was developed at Micron Research, in Australia (8). The Micron method involves pretreatment of loaded carbon, with a caustic cyanide solution followed by elution with an alcohol mixture.

The Micron elution procedure takes advantage of the enhanced stripping rate achieved with alcohol, but confines the alcohol to the closed stripping unit. Fire dangers are reduced quite substantially, as the pregnant eluant that is subsequently processed for gold recovery does not contain alcohol.

The elution unit is configured like a packed bed distillation tower with a heater on
the base of the column, an overhead condenser, a reflux pump and the loaded carbon functioning as the tower packing.

Loaded carbon is first presoaked with sodium cyanide/sodium hydroxide solution. The presoak solution is drained from the carbon bed and an alcohol solution is added to the vessel.

The unit is then switched to the batch distillation mode. Within a few hours, the
alcohol is concentrated in the overhead condenser tank. 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.

The Micron process consists of the following operations (See Figure 7):

(1) Presoak

The carbon is first soaked in a solution of 1 to 2 % sodium hydroxide and 5 to 10 % sodium cyanide at ambient temperature. Carbons with particularly high concentrations of gold, silver, or copper may require solutions containing up to 20% sodium cyanide. The solution is then drained from the carbon until free of excess moisture.

(2) Desorption

About 0.5 Bed Volume of alcohol is added after the carbon bed has drained. Methyl alcohol is used in the majority of applications, but ethanol is occasionally applied. Acetonitrile may be substituted for the alcohol, but its higher cost generally discourages its use.

Heat is then applied to the base of the desorption vessel. Organic vapors rise through the carbon bed and are condensed in the overhead condenser. The condensate is pumped back to the top of the carbon bed and is sprayed on the carbon. The downflowing condensate washes the gold values from the carbon particles into the boiler section below.

(3) Alcohol Recovery

When desorption is completed, as indicated by gold solution concentration reaching a constant level in the column boiler, alcohol recovery commences. The condensate recycle spray is stopped and the alcohol is allowed to boil out of the pregnant solution. The boiling is terminated when the temperature in the boiler rises to the boiling point of the water solution. The pregnant liquor is then drained from the desorption vessel. The carbon is then steam stripped to recover residual alcohol.

The Micron process produces a very concentrated eluant free of alcohol, with gold and silver values two or three times higher than those in the loaded carbon. This is in direct contrast with the Zadra and AARL procedures, which produce eluant concentrations one or two orders of magnitude lower. The high solution grades make recovery methods such as chemical precipitation and aluminum foil electro-deposition very attractive.

The micron eluted carbon also appears to have a somewhat higher level of activity than carbon eluted by other methods. This may reduce the need to reactivate carbon as frequently at some operations.

The entire stripping cycle takes about 8 hours. Over 20 licenses for this process have been issued, but none are in the United States.

VII. VARIATIONS

There are numerous variations to, and combinations of, the basic processes as
illustrated by the following:

(1) Glycol or alcohol are sometimes added to pressure strip or AARL strip operations to increase stripping rates.

(2) A caustic/cyanide presoak may be used in a Zadra system.

(3) A hot water wash is sometimes used at the end of a pressurized Zadra strip to gain some of the advantage of the water elution used in AARL stripping.

(4) In situations where large amounts of copper load onto carbon with the gold and
silver, a two stage strip may be beneficial. Copper may often be selectively eluted with a cold caustic/cyanide solution. This is then followed by one of the standard stripping methods.

(5) Carbon is normally stripped batch wise, but moving bed continuous elution systems have occasionally been used with both Zadra and AARL procedures.

(6) Electrowinning may be done under pressure to avoid repressuring solution on each pass through the carbon.

(7) Zinc precipitation may be substituted for electrowinning.

CONCLUSIONS & RECOMMENDATIONS

Each new project should be evaluated individually to determine the best procedure for the particular ore and site specific circumstances.

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. It may also be preferred for areas where extreme ease of maintenance and operability are a priority due to a lack of skilled manpower.

The pressurized Zadra system has recently been the preferred process in the United States for most medium to large sized projects. This is due to its significant cost advantage over atmospheric pressure Zadra systems.

The AARL process is the preferred process in Australia and South Africa, except where water balance or water quality problems exist. Several recent United States projects have also elected to use AARL systems. The AARL process should definitely be considered for large projects with sophisticated operators.

Alcohol stripping has generally fallen out of favor due to the flammability concerns.
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.

Source: http://www.denvermineral.com/carbon-stripping/