At present, there are many methods for desorbing gold from gold- loaded carbon commonly used in industry at home and abroad. According to different formulation and technical conditions, it can be divided into the following six types:
1. Atmospheric alkali-cyanide desorption method The desorption agent of the method is NaOH, NaCN aqueous solution, and its concentration is generally NaOH: 1 to 1.5%; NaCN: 0.2 to 0.3%. The desorption temperature is controlled at 85-90 ° C, the volume ratio of the desorbed liquid to the gold-loaded carbon is 8-15, and the speed of the desorbed solution is generally 1 to 2 bed volume/hour, which is operated by means of desorption and electrolyte circulation. . The desorption time is 50 to 72 hours.
The advantage of this method is that the equipment is relatively simple, the operation is convenient, and the cost of the medicine is low. The disadvantages are slow desorption and low equipment productivity.
2. Atmospheric alkali-ethanol (methanol)-cyanide desorption method This method uses sodium hydroxide, sodium cyanide and ethanol (methanol) aqueous solution as a desorbent, the concentration of which is 1-2%, 10%, 15-20 % (volume percent). The desorption temperature is controlled to be 82 to 85 °C. The volume ratio of the desorbed liquid to the gold-loaded carbon is about 8. The desorption time is 12 hours.
The advantage of this method is that the desorption rate is fast and it is not necessary to use high voltage equipment. The disadvantage is that the alcohol consumption is large, and the alcohol is easily volatilized during the desorption process of the activated carbon, so that the cost is increased. At the same time, it is easy to cause burning, which is not conducive to safe production. Furthermore, activated carbon desorbed with ethanol has a reduced activity.
3. Pretreatment with high concentration alkali-sodium cyanide aqueous solution, deionized water or demineralized water washing and desorption method using high concentration alkali and sodium cyanide aqueous solution, the concentration is 1 ~ 5%, 1-2%, at 90 ° C Soak for 30 minutes at a temperature, the volume ratio of the pretreatment liquid to the gold-loaded carbon is 1, then the pretreatment liquid is discharged, and then deionized water or demineralized water at a temperature of 100 to 200 ° C is used for 0.5 to 2 beds of carbon volume per hour. The gold-loaded charcoal is washed at a speed, and the amount of the washing liquid is 3 to 5 bed carbon volumes. The desorption time is 3 to 12 hours, and the washed precious liquid is combined with the discharged pretreatment liquid for electrolysis.
The method can be operated by a pressurizing operation or a normal pressure, but the desorption speed of the former is fast.
The advantage of this method is that the desorption rate of gold is fast, the amount of desorption liquid (including pretreatment liquid and washing water) is small, and the gold concentration of the noble liquid is high. The disadvantage is that the pretreatment liquid and the washing liquid must be combined for electrolysis and cannot be continuously operated.
4. Pressurized alkali-cyanide desorption method The sodium hydroxide and sodium cyanide used in the method have a concentration of 0.5 to 1%, 0.1 to 0.2% in an aqueous solution, a desorption temperature of 130 to 140 ° C, and a pressure of 3 to 4, respectively. In kilograms/cm ² , the volume ratio of desorbed liquid to gold-loaded carbon is 8-15. The desorption time is related to the temperature and pressure of the operation. When the temperature is 140 ° C, the desorption time is about 6 hours, and the low temperature takes a little longer.
The advantage of this method is that the desorption rate is fast, the dosage of the medicament is small, and the utilization rate of the equipment is high. The disadvantage is that the use of pressurized equipment increases the cost and investment, and the operation is complicated and the security is poor.
5. Pre-acid washing, then alkali-cyanide desorption method. The method is to pre-wash the gold-loaded carbon with hydrochloric acid, remove the calcium carbonate and iron on the gold-loaded carbon, and then wash the acid and impurities with water, then use sodium hydroxide. The sodium cyanide aqueous solution desorbs gold. The method can be desorbed under normal pressure or pressure. First, it was immersed in hydrochloric acid for 1.5 hours, and then washed with 5 times of gold-loaded carbon water, and desorbed by various desorption methods described above.
The advantage of this method is that, due to the removal of calcium and iron ions in advance, a relatively pure desorbed noble liquid can be produced, and gold is completely desorbed. At the same time, since the impurities are removed, the regenerated charcoal having higher activity can be obtained. The disadvantage is that the equipment needs to be preserved, hydrochloric acid is consumed, and the operation is complicated.
6. Non-cyanide desorption method There are many researches in this area, such as the solution of Na ₂ CO ₃ + NaOH or the solution of Na ₂ S + NaOH as a desorbent, which is widely used in industry. Desorption was carried out for 12 hours at a temperature of 83 ° C with 1% strength NaOH plus 20% by volume of ethanol as a desorption solution, which has been used industrially. Although the method does not use cyanide to achieve non-toxic desorption, but due to the use of ethanol, it will inevitably bring a series of problems.

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