RU2208579C1 - Activated carbon manufacture process - Google Patents

Abstract

FIELD: carbon materials. SUBSTANCE: invention relates to manufacture of activated carbons useful in freeing water of harmful impurities and recovering precious metals (gold, silver, platinum) from solutions and pulps. Process comprises mixing, at 60-80 C, pulverized coal with phosphoric acid- containing binder at volume ratio 1:(0.22-2.35), granulation of mixture, carbonization of granules, isothermal ageing thereof at 750-850 C during 1.5-3.0 h, and steam activation until summary pore volume 0.82-0.90 cu.cm/g is reached. EFFECT: improved kinetic properties without loss in mechanical strength. 2 tbl, 3 ex

Description

 The invention relates to the field of adsorption technology and can be used in the synthesis of coal for working in liquid media (water, pulp solutions, etc.), especially in hydrometallurgical processes for the extraction of gold and other noble metals.

A known method of producing activated carbon (a.u.) for working in liquid media, including mixing a carbon-containing material with a binder, granulating the paste, carbonizing the granules at a temperature of 450-600 ^o C and activating water vapor to a total pore volume V _Σ = 0.55 -0.75 cm ³ / g, cooling of the granules, washing with hydrochloric acid, drying and sieving (US Pat. RF 2111165, class C 01 B 31/08, 05/20/98).

 The disadvantage of this method is the complexity and multi-stage process and significant environmental pollution by washing water, the relatively low strength of the obtained sorbents.

Closest to the proposed technical essence and the achieved result is a method for producing activated carbon, comprising mixing coal dust and a binder containing phosphoric acid 2.2-6.0 wt. % and heated to 60-95 ^o C, granulation of the paste, carbonization of granules in the temperature range 250-750 ^o C and their activation at 850 ± 50 ^o With water vapor or a mixture of its carbon dioxide (US Pat. RF 2156731, class C 01 V 31/08, 09/27/2000).

 This method is adopted as a prototype of the invention.

 The disadvantage of this method is the low kinetic characteristics of the process of extracting gold and silver in the hydrometallurgical industry, which is due to both the long half-life of the adsorption capacity of coal and the duration of desorption of precious metals. All this contributes to the cost of the resulting final products and the formation of unused metal residues in the pores of activated carbon.

 The aim of the invention is to increase the kinetic characteristics of activated carbon used in the processes of extraction of precious metals, while maintaining its high strength properties.

This goal is achieved by the proposed method, including mixing coal dust with a binder containing phosphoric acid, with a volume ratio of 1: 0.22-0.35, and a temperature of 60-80 ^o C, granulation of the paste, carbonization of granules, keeping them before activation at a temperature of 750-850 ^o C for 1.5-3.0 hours.

The difference of the proposed method from the known one is that coal dust (base) and a phosphorus-containing binder are taken at a volume ratio of 1: 0.22-0.35, mixing is carried out at a temperature of 60-80 ^o C, instead of 1: 0.18 -0.20 and 25-40 ^o C, respectively.

Another difference lies in carrying out an additional stage before activation - keeping carbonized granules at 750-850 ^o C for 1.5-3.0 hours.

The authors do not know a method for producing granular coals on a coal-based basis, in which carbon dust and a binder are taken in a volume ratio of 1: 0.22-0.35, and mixing is carried out at elevated temperatures of 60-80 ^o With the whole paste, and not the binder.

Unknown and the method of isothermal exposure of carbonized coal-tar granules containing phosphoric acid at a temperature of 750-850 ^o C for 1.5-3.0 hours.

In the synthesis of carbon adsorbents for noble metal hydrometallurgy, especially for pulp processes (i.e., simultaneous mixing of activated carbon and crushed ore in cyanide solutions), they tend to obtain the most dense granules with a total pore volume of not more than 0.60-0.63 cm ³ / g to ensure high strength properties of the adsorbent and to reduce its abrasion, cracking and dust.

 However, in the case of extraction of gold and silver from solutions, for example, during heap leaching, such adsorbents exhibit unsatisfactory kinetic properties, which significantly increases the cost and length of the extraction of valuable products.

 From the scientific and technical literature it is known that the kinetics of adsorption is determined by two main parameters: the half-life of the adsorption capacity of coal and the time of desorption of gold and silver into solution (see N.V. Keltsev. "Fundamentals of adsorption technology. Moscow, Chemistry, 1976, p. .179-205; V. M. Mukhin, A. V. Tarasov, V. N. Klushin. “Active Coals of Russia.” Moscow, Metallurgy, 2000, pp. 266-270.

 Numerous experiments undertaken to improve the kinetic properties of granular sorbents on a coal-based basis without reducing their strength characteristics have shown that they substantially depend on the volume ratio of the taken components-coal base (dust) and a liquid binder containing phosphoric acid, mixing temperature, speed feeding the paste to the granulator; carbonization and activation conditions.

It was found that the determining parameters when achieving the objective of the invention are: the volume ratio of coal dust and binder, which should be equal to 1: 0.22-0.35, as well as the mixing temperature of these components, which should be 60-80 ^o C. These the conditions ensure the formation of rational primary porosity (with a certain ratio of micro- and mesopores), which is fixed (fixed) during the subsequent technological stages.

Additional heat treatment of carbonized granules at 750-850 ^o C for 1.5-3.0 hours allows you to remove the residual volatile content (15-20%) and lower reactivity, which ensures the preservation of high strength properties of the obtained active carbons.

 The method is as follows.

 Coal (or a mixture of it with a semicoke is crushed in a ball mill and dosed by volume into a granulator-mixer, a resin binder is poured there, representing a composition of wood-chemical (coal) resin (96-97%) and phosphoric acid (3-4%) .

The volume ratio of coal dust and resin is taken equal to 1: 0.22-0.35. The resulting paste mixture is heated to 60-80 ^o C and, after thorough mixing, granulated through filters with a hole diameter of 1.8-2.8 mm The obtained "raw" granules are sent to the oven and heated to 750-850 ^o With a lifting speed of 25-40 ^o C / min, at a temperature of 750-850 ^o With carbonized granules incubated for 1.5-3.0 hours, after which activated with steam for 6-8 hours to a total pore volume of 0.82-0.87 cm ³ / g

 The following examples illustrate the invention.

Example 1. Take 10 liters of coal dust ("CC", GOST 10355-84), which is poured into a mixer-granulator having a steam jacket, 2.2 liters of coal tar containing 3% phosphoric acid are poured there, then served in the shirt water vapor and the mixture with stirring (2 min) are heated to 60 ^° C. Then they are granulated through nozzles having a diameter of 1.8 mm.

The obtained granules are placed in a stationary vertical furnace and carbonized, raising the temperature from room temperature to 750 ^o With a speed of 25-40 ^o C / min At 750 ^{° C., the} carbonate is held for 1.5 hours and the temperature is raised to 850 ^{° C.} , steam (5-6 kg / kg) is supplied and activated for 6 hours to a total pore volume of 0.82 cm ³ / g. Then activated carbon is discharged, cooled and its mechanical strength and kinetic characteristics are measured, namely, the half-life of coal and the time of gold desorption into solution under standard conditions:
- the volume of the solution is 0.5 l / min;
- mass of coal - 0.5 g;
- temperature - 20 ^o C;
- initial concentration C ref. - 10 mg / dm ³ ;
- saturation of coal with gold - 20 mg / g.

Activated carbon obtained by the method described in example 1 is characterized by the following indicators:
- half-life - 4.5 hours;
- complete desorption - 14 hours;
- mechanical strength - 95%.

The kinetic characteristics of activated carbon obtained by the prototype (US Pat. RF 2156731, class C 01 In 31/08, 09/27/2000), have the following values:
- half-life - 6.5 hours;
- complete desorption - 18.5 hours.

 Mechanical strength - 95%.

Example 2. Analogously to example 1, except that the ratio of coal dust and binder is: 10 liters of dust 3.5 liters of resin (1: 0.35), a stirring temperature of 80 ^o C. The carbonate is heated to 850 ^o C and kept at this temperature is 3.0 hours, activation is carried out to a total pore volume of 0.87 cm ³ / g.

Kinetic characteristics of coal:
- half-life of coal - 4.0 hours;
- the time of complete desorption of gold in solution is 11 hours.

 The mechanical strength of coal is 94.9%.

Example 3. Analogously to example 1, except that 2.9 liters of resin are taken (the ratio is 1: 0.29), the stirring temperature is maintained at 70 ^{° C.} , the isothermal exposure time at 800 ^{° C.} is 2.2 hours. Coal is activated to a total pore volume of 0.85 cm ³ / g.

Unloaded activated carbon has the following indicators:
- half-life - 4.2 hours;
- the time of complete desorption of gold in solution - 11.5 hours;
- mechanical strength 95%.

In the table. 1 presents examples obtained analogously to example 1 on the influence of the volume ratio of coal dust and binder on the quality of the obtained coals. In these examples, the stirring temperature was 60 ^o C.

 As follows from the above data, the ratio of the coal base and the binder, equal to 1: 0.22-0.35, leads to an improvement in the kinetic characteristics of the resulting coals. A decrease in the volume of the binder below 22% (by volume) or an increase above 35% does not lead to the achievement of the goal.

Table 2 presents the results of the influence of the isothermal exposure time of carbonized granules at 750 ^o С on the quality of the obtained coals. All other parameters are similar to example 1.

 From the data table. 2 it follows that the isothermal exposure time equal to 1.5-3.0 hours, contributes to a significant improvement in the kinetic properties of the obtained coals while maintaining their high mechanical strength. Reducing the exposure time (below 1.5 hours) worsens the strength of the products obtained, and increasing the exposure time (more than 3.0 hours) causes an increase in the time of desorption of gold into the solution.

 The experiments also showed that the quality of the coal is significantly affected by the mixing time (2-5 minutes), the rate of rise of the pores of the coal and the degree of burning.

It follows from the foregoing that each of the features of the claimed combination to a greater or lesser extent affects the achievement of the goal, namely, the improvement of the kinetic properties used in the extraction of gold, silver and other noble metals, while maintaining their high mechanical strength. And the whole set: the volume ratio of coal dust and binder as 1: 0.22-0.35, the mixing of components at an elevated temperature of 60-80 ^o C and isothermal exposure of carbonized granules at 750-850 ^o C for 1.5-3, 0 hours is sufficient to characterize the claimed technical solution.

Claims (1)

A method for producing activated carbon, comprising mixing coal dust with a binder containing phosphoric acid, granulating the mixture, carbonizing the granules and activating them, characterized in that the mixing of dust with a binder is carried out in a volume ratio of 1: 0.22-0.35, and a temperature of 60-80 ^o C, and before activation, carbonized granules are kept at a temperature of 750-850 ^o C for 1.5-3.0 hours

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