Activated carbon regeneration technology (2)

Since the minimum pore size can be measured iodine value is about 10 angstroms, and a pore size adsorbing gold cyanide complex required similar, so iodine value can reflect the performance of the activated carbon adsorption of gold cyanide complex. However, the national standard for determining the iodine value requires that the activated carbon be ground into a -200 mesh powder before it can be measured, which is quite different from the conditions for adsorbing gold. The adsorbed gold is made of granular activated carbon, and its particle size is generally 6 to 16 mesh, which is quite different from -200 mesh. In other words, the performance that can be reflected by the measured iodine value is actually not due to kinetic reasons. All of them are actually used, only 25 to 50% are used . This explains that although the iodine value of regenerated carbon is often lower than 800 mg/g , its adsorption performance is not worse than that of new carbon or even more than new carbon.

    In addition to having a high surface area, a large pore volume and a small pore size, the gold-added activated carbon requires a higher strength to facilitate the use in the slurry for a long period of time with less wear.

4 adsorption mechanism of activated carbon [ 1 ]

    The adsorption properties of activated carbon depend mainly on the large internal surface area and pore distribution of activated carbon. Its outer surface area and surface oxidation state are less effective, and the outer surface merely provides a channel that communicates with the inner cavity. The primary role of surface oxides is to render the hydrophobic carbon backbone hydrophilic, giving the activated carbon an affinity for many polar and non-polar compounds. Activated carbon, like many porous objects, is caused by an unbalanced force on the carbon atoms that make up the surface of the pore wall. Thereby adsorbing certain substances. The larger the surface area having such an effect, the better the adsorption performance.

    There are two adsorption processes: physical adsorption and adsorption. Physical adsorption is related to the interaction between dipoles and weak van der Waals forces dominated by hydrogen bonds, which are reversible. Chemical adsorption is irreversible and it is combined by valence bonds. Adsorption is an exothermic process. In most cases, the adsorption of activated carbon is a type of physical adsorption.

    The adsorption kinetics are controlled by diffusion. It is necessary for the adsorbed molecules or ions to reach the inner surface of the micropores by diffusion, and therefore, the reaction time is controlled by the length of the diffusion path. Since the pores of the gold-added activated carbon are generally around angstrom, and the volume of the gold-cyanide complex ions is large, the diffusion to the inner surface of the activated carbon undergoes a tortuous and slow diffusion process.

    The adsorption mechanism of gold cyanide ion in activated carbon has the following types of hypotheses:

a adsorbing its ion pair;

b decomposition to produce insoluble AuCN ;

c is adsorbed by the electric double layer on the charged surface and partially reduced to the cluster component.

    During the adsorption of gold cyanide ions, a large number of other metal (complex) ions, anions (such as arsenate ), organic matter (such as engine oil) are adsorbed in the activated carbon, affecting the adsorption equilibrium of gold; The deposition of substances such as calcium carbonate, calcium silicate, and calcium sulfate blocks the pores of the activated carbon and hinders the diffusion of gold into the pores. These substances are desorbed or partially desorbed during the desorption of gold activated carbon (heavy metal complexes, silicates), which reduces the adsorption rate and adsorption capacity of the gold cyanide complex when the activated carbon is reused. Therefore, the activated carbon must be regenerated to ensure the performance of the activated carbon adsorption gold.

5 selection of gold extraction activated carbon [ 1 ], [ 3 ]

    First, it is necessary to have good characteristics of gold adsorption, and second, it requires good wear resistance of carbon particles. The former is necessary to effectively extract gold from the solution, which is necessary to adsorb gold in the slurry. In the pulp, the activated carbon wear not only loses the activated carbon but also carries away the adsorbed gold on the lost char. It is worth emphasizing that most of the charcoal that is rubbed in the carbon slurry is charcoal on the surface of the activated carbon, and the gold grade is high, so the amount of gold loss is large.

The requirements for adsorbing gold activated carbon are as follows:

Gold grade: kg/t . Carbon ( measured in a 1 mg/L gold cyano complex ion solution for 24 hours)

Gold adsorption rate: 60% gold adsorption in 1 hour (measured by stirring adsorption conditions in 10 mg/L gold cyanide ion solution)

Abrasion resistance: less than 2% (measured by the roller bottle method within 24 hours)

Carbon particle size: 6 to 16 mesh.

    Activated carbon produced by different manufacturers and produced in different batches has certain differences in properties. Only from the desorption time, the desorption time of apricot nuclear charcoal is only 18 hours; the desorption time of coconut shell charcoal in a professional factory is 24 to 28 hours; Some coconut shell charcoal desorption time is up to 42 hours.

    The length of the desorption time reflects the difference in the size of the pores in the activated carbon, and also reflects the large difference in the length of the pores (when the gold-loaded carbon is seriously polluted, the desorption rate is also reduced).

6 regeneration method of activated carbon

a acid dipping method [ 1 ], [ 4 ], [ 5 ]

    It is mainly used for the inorganic substances such as carbonates on activated carbon, which are dissolved by pickling to achieve the purpose of regeneration. It is usually soaked in 3 to 5% hydrochloric acid and then washed to neutrality. An example of regeneration with nitric acid is also used, the effect of which is similar to that of hydrochloric acid.

b high temperature regeneration method [ 1 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ]

    The organic matter on the charcoal cannot be washed away with acid and alkali. The activated carbon must be heated at a high temperature under the condition of insulating air. It is generally considered that: 650 °C ~ 850 °C The heating can be achieved by heating for 30 minutes. The regeneration process can also be activated by steam, but it is also activated without steam. Due to different regeneration methods, it is impossible to compare the effects of different temperatures and times.

7 types of activated carbon regenerator

    Since the application of activated carbon in the gold industry, the regeneration of activated carbon has been an urgent problem to be solved. Foreign countries have developed rotary tubular regenerative furnaces using electricity or coal as heat sources, and vertical thermal regeneration using coal or coke as fuel. Furnace, electric regenerative furnace that relies on the resistance of activated carbon to heat it, and multi-tube regeneration equipment that uses gas or fuel as heat source [ 10 ]. These devices are widely used in the United States, South Africa, Canada and Australia, and have achieved good technical and economic results.

In China, the old electric heating rotary furnace has high power consumption (4 kwh / kg carbon), excessive carbon loss (more than 15%), unstable regeneration effect, small processing capacity and easy equipment damage, and now rarely used; The intermittently produced vibrating regenerative equipment with self-resistance and heat generation is complicated, unstable in operation, easy to damage, and difficult to maintain, and the power consumption is 1.5kwh/kg . Although the gold mine currently has a quantitative advantage, the user's satisfaction is poor; another continuously operating equipment cannot enter the market on a large scale for similar reasons; the patent for a new type of regenerative furnace using resistance heating is applied by a unit in the south. The structure is more complicated and still can not meet the needs of the market; and the vertical regenerative furnace developed by using the self-resistance heating of activated carbon in 1997 also has complicated automatic control equipment, vulnerable parts, unstable operation and high price (25Kg). /h processing capacity of the furnace each 50,000 yuan or more) shortcomings, did not occupy the market. The regenerative furnace of vertical coal or coke fuel used by activated carbon manufacturers is not suitable for use in gold mines due to its large volume and difficult transportation of manufactured materials.

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