The processes of extracting gold from cyanide pulp or solution by activated carbon adsorption method include: carbon slurry method (CIP method for short), carbon leaching method (CIL method) and carbon column method (CIC method for short), and their processes are basically The above steps include the following steps: (1) leaching gold from activated carbon by cyanide slurry or solution to produce gold-loaded charcoal; (2) desorbing the gold-loaded charcoal to re-transfer the gold on the charcoal into the solution. In the middle, the gold is desorbed from the precious liquid; (3) the gold is recovered from the gold-containing precious liquid by various methods; (4) the depleted charcoal after the desorption is regenerated, and its activity is restored, and then returned to the adsorption operation for reuse. .
1 characteristics of activated carbon
Activated carbon is divided into powder carbon and granular carbon from the appearance. Granular carbon can be produced from a variety of carbonaceous materials such as various celluloses, wood, coconut shells, husks, fruit cores, and various coals .
The research work shows that the structure of activated carbon is similar to that of graphite . It is composed of tiny wafers. The thickness of the wafer is only a few carbon atoms thick, 2 to 10 microns in diameter, and the arrangement is very irregular. It has many molecules with a large size. The side wall of the open aperture. Therefore, activated carbon is an active material having a developed pore structure and a large adsorption surface machine, which is Au(CN)-a good adsorbent. The pore structure of activated carbon is very complicated, ranging from 10 to 100 in diameter.
The surface area of ​​activated carbon is an important indicator to determine its adsorption capacity. It can usually be expressed by the specific surface area (m 2 / gram). The surface area of ​​activated carbon is composed of the outer surface of the particle and the inner surface composed of pores. The internal surface area of ​​the structure has a large area ratio (greater than 90%), and thus has a decisive effect on the adsorption characteristics of activated carbon. The specific surface area of ​​activated carbon is determined to be large, generally 500-1400 m 2 /g, and some Even up to 2500 m 2 / g.
In the gold extraction production, the activated carbon required to have high hardness and wear resistance, and the adsorption activity and wear resistance are often contradictory. In production practice, it is often determined by experiment and experience to determine which activated carbon to use.
2 adsorption process of activated carbon
It is completed by three steps of Au(CN)-outward diffusion to the surface of the carbon particles, internal diffusion and adsorption into the interior of the carbon particles.
3. Factors affecting the adsorption of activated carbon
3.1, the type of activated carbon
The adsorption characteristics of coconut shell charcoal and apricot kernel charcoal are much better than those of coal charcoal and charcoal charcoal.
3.2, adsorption equipment structure
Common adsorption tanks have axial flow and runoff types. In comparison, the axial flow groove has less resistance, the dead zone is also small, and the carbon wear rate is also low, especially when the double impeller is used.
3.3, pulp properties
Refers to the particle size characteristics, concentration and viscosity of the slurry, the content of organic matter, the pH of the slurry, and the like.
The grain size characteristic of the slurry means that the pulp often contains some wood chips or coarse ore sand which is larger than the size of the inter-layer sieve hole, which will cause the blockage of the inter-stage sieve holes and the grade of the gold-loaded carbon. In addition, the gold-loaded charcoal containing wood chips The desorption rate is not high.
The concentration of pulp mainly affects the specific gravity and fluidity of the slurry, which will directly affect the floating and unbalanced distribution of activated carbon, which is not conducive to adsorption. It has been proved that the general control is better at 40~45%.
The viscosity of the pulp is mainly determined by the content of the fine mud. The mud is rich, the viscosity is large, and the fluidity is poor. It is easy to cause blockage of the interstage sieve, and at the same time, the adsorption effect is not good.
The organic matter in the pulp mainly refers to wood chips, oil substances, humic acid, flotation chemicals and the like. They can be adsorbed by activated carbon, affecting the adsorption rate of gold, and poisoning activated carbon, which makes it difficult to activate and regenerate carbon.
3.4, the number of adsorption sections and the concentration of bottom carbon
The number of adsorption sections and the concentration of bottom carbon are generally determined by experiments and experience. The number of adsorption faults is generally 4 to 6 segments, and the concentration of bottom carbon is controlled between 5 and 25 grams per liter. Countercurrent series carbon (intermittent and continuous) is used. ).
3.5, slurry inflating
The amount of slurry inflated is too high to reduce the leaching speed of gold and the adsorption of gold by activated carbon. The inflation method generally has two kinds of central inflation and pipeline inflation, and the time proves that the axial center inflation method is better.
4 carbon lifting equipment and process operation
4.1, carbon lifting equipment
Currently used are three types of turbo pumps, jet pumps, and air mixing chambers.
4.2, process operation
The charcoal is generally started from the first tank, then the charcoal is extracted in series by tank, and finally the charcoal is added in the last tank. The number of carbon removal is based on the test and theoretical calculation, and the shifts are unified.
Desorption of 5 gold charcoal
5.1, the principle of desorption of gold-loaded charcoal
The experimental research proves that the process of adsorption of activated carbon is actually a reversible process. When carbon adsorbs gold, the temperature, pressure, pH value and cyanide (CN-) concentration will be too high, which will reduce the amount of gold adsorption, so it can be effective. The method allows the gold on the gold-loaded charcoal to be desorbed into the solution.
5.2. Desorption method and process conditions of gold-loaded carbon
5.2.1, atmospheric pressure heating desorption method (also known as Zhadra desorption method)
This is the simpler method that first appeared. At a temperature of 85-95 ° C, a mixed aqueous solution prepared with 0.1% NaCN and 1.0% NaOH is passed through a gold-loaded carbon bed, and the desorption requirement is about 28 to 70 hours.
5.2..2, pressure desorption method
The temperature is 150~1700C, the pressure is 0.3432Mpa, the mixed aqueous solution is prepared by 0.1% NaCN and 0.4~1.0% NaOH. Desorption of 4~6 hours can make the decarbonization gold content lower than 50~70g/ton. The cycle of this law is not long, but the equipment costs are high, and the desorption of the noble liquid must be cooled before it is sent to the electricity.
5.2.3, alcohol desorption method
With a mixture of 1.0% NaCN and 1.0% NaOH, 20% by volume of alcohol was added, and desorption was carried out at 800 C under normal pressure. The desorption time was 5-6 hours, but alcohol was flammable and volatile, and it was difficult to control.
5.2.4, the United States and Britain desorption method
The method was initiated by the Anglo-American Institute of South Africa. The gold-loaded charcoal was pretreated with 0.5 5% and 1.0% mixed volume of gold-loaded carbon for 0.5 to 1 hour, and then heated with 5 volumes of gold-loaded deionized water. Desorption at a flow rate of 3 loaded gold bed volumes per hour, operating temperature 1100 C, operating pressure 0.5-1.0 kg/cm 2 , desorption time (including acidity) approximately 9 hours.
5.3, desorption equipment and operation precautions
The gold-loaded desorption equipment is usually associated with an electrolytic deposition apparatus to form a production cycle unit.
The prepared gold-loaded charcoal is charged into the desorption column (column), and the prepared desorbed liquid is pumped into the desorption electrowinning system, and the specific operation mode depends on the equipment and process used.
5.4, ​​matters needing attention in desorption of gold charcoal
5.4.1. When the aspect ratio of the desorption tower is greater than 6, the desorption effect is better, the operation is convenient, and the desorption time is shortened. Therefore, a desorption tower having a length to diameter ratio of more than 6 is generally used.
5.4.2. The flow state of the desorbed liquid in the tower should be as uniform as possible in the inner section of the tower and fully in contact with the gold-loaded charcoal.
5.4.3. Select the appropriate desorption time by experiment. In general, the longer the desorption time, the higher the desorption rate, but if it is too long, the equipment utilization rate will be reduced and the production cost will increase.
5.4.4. Strictly control the desorption temperature according to the requirements of the regulations.
5.4.5, to ensure that the composition of the desorbent meets the requirements
5.4.6, pay attention to the flow rate of desorbent, generally 1 to 5 carbon bed volume in 1 hour.
5.4.7. Pay attention to the impurity-containing conditions and pore characteristics of gold-loaded carbon. Pre-exclusion of impurities in wood (wood chips, plastics, coarse ore, etc.) will contribute to the improvement of desorption rate.
6, regeneration of gold removal
The activity of activated carbon is obviously expressed after adsorption, desorption and regeneration. After acid regeneration, the activity of decarbonized carbon is not significantly improved, and only half of the activity can be restored. Only by thermal regeneration, the activity can be restored to 80. %the above.
The main reasons for the decrease in the adsorption activity of activated carbon are as follows;
First, the pores of carbon are blocked by inorganic substances, such as Ca(OH)2, Mg(OH)2 quartz sand particles in the slurry, clay clay mud, etc., which are easily adsorbed by activated carbon and enter the pores of the carbon to produce channels. Blockage, in addition to the excessive amount of complex ions in the slurry and copper and other base metals, will also be caused by the adsorption of carbon particles to cause micropore poisoning, reducing activity.
Second, organic matter such as lubricating oil, detergent, flotation reagent, humic acid, etc. are all adsorbed by activated carbon, which greatly affects the activity of carbon.
Third, the degradation of active sites in activated carbon and the formation of pores in carbon are also responsible for the decrease in activity.
Practice has proved that after deamination of gold, its activity can be restored to 50-60%, and its activity can be restored to more than 85% after thermal regeneration, and some even better than the activity of new carbon. The acid can be diluted with hydrochloric acid or dilute nitric acid (concentration 1~5%) at a normal temperature in a special pickling tank. After 2~4 hours of washing, the compound such as calcium and zinc on the carbon can be removed, and the hot acid at 90~93 °C is used. The solution removes calcium, zinc, nickel compounds and most of the silicon. If the pores of the charcoal are severely clogged with silicate, only hydrofluoric acid (HF) aqueous solution can be used.
The thermal regeneration of the de-carbonized carbon is usually completed in an external thermal rotary furnace. The process includes several stages of drying, carbonization and gasification, which can play the following roles:
First, the organic adsorbate is desorbed and volatilized during the heating phase;
Second, the organic pollutants are carbonized at 600~700 °C;
Third, carbon forms new micropores and increases the specific surface area;
Fourth, a new activation point is formed in the pores of the carbon to increase the activity.
Toothbrush Sterilizer,Uv Toothbrush Sterilizer,Smart Toothbrush Sterilizer,Electric Toothbrush Sterilizer
Yiwu Waterfilter Industry And Trade Co.,ltd , https://www.aqua-water-filter.com