Common desorption method for gold-loaded carbon - alkaline ethanol solution desorption method
The alkaline ethanol solution desorption method is to add 20% ethanol (or propanol) in a mixed solution of 1% NaOH and 0.1% to 0.2% NaCN, and desorb at 64 ° C under normal pressure desorption within 6-8 hours. The volume of the desorbent and the washing liquid is only 7 to 10 times the bed volume. Practice has shown that desorption with an alkaline ethanol solution can reduce the number of carbon regenerations. However, ethanol is flammable and explosive, and strict safety measures should be considered. Increasing the recovery of alcohols is critical to reducing the cost of the alcohol solution desorption process.
The alkaline ethanol solution desorption method successfully studied by the nuclear industry uses 40% to 50% ethanol, the temperature is 78-80 ° C, NaOH 1% to 2%, NaCN 0.5% to 1.0%, and desorption at atmospheric pressure. Soak the gold- loaded charcoal with the above solution for 1 to 2 hours, and then soak it once with 30% to 35% of the ethanol solution. The solutions of these two operations were successively placed in a distillation still for distillation. The distilled steam passes through the desorbed carbon layer, and the ethanol vapor is cooled by the condenser into an alcohol solution and flows into the alcohol storage tank. The distilled alcohol recovered by the pump is pumped to the desorption dome and flows through the carbon layer from top to bottom. Repeated distillation 3 to 4 times to complete a desorption cycle, generally 8 ~ 10h. The desorption rate is greater than 98% and the recovery of ethanol is greater than 90%. The concentration of the rich liquid gold obtained by this method can reach 5-8 g ∕L (the gold grade of the char). Therefore, the current efficiency during electrolysis is also higher than other methods. Since the alcohol vapor repeatedly passes through the carbon layer during desorption, it is beneficial to restore the activity of the carbon, and the desorbed carbon can be reused without high-temperature regeneration.
In recent years, Caps-Kahid United has successfully developed a mobile adsorption desorption device suitable for small and medium-sized heap leaching operations, as shown in Figure 1. The main equipment consists of six carbon adsorption/rinsing towers, power supply and various storage tanks. It is packed in two containers for easy on-site movement and installation. Its greatest feature is that both adsorption and desorption are carried out in the same equipment, without the need to transfer charcoal. The left side of the figure is a schematic diagram of the four-column series adsorption, and the right side is a schematic diagram of the two towers desorption.
Figure 1 Six towers process and equipment
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