METHOD FOR METAL LEACHING

TECHNICAL FIELD

This invention relates to a method for metal leaching of metal-containing materials such as ores, concentrates, industrial waste, and semi-finished products by subjecting them to ultrasonic field energy.

BACKGROUND OF THE INVENTION

Hydrometallurgical methods are known that are used for extraction of metals by treating the metal-containing material with water-based solutions of chemical reagents, subjecting it to ultrasonic intensity. Such a method is described in BG 64159 where at each stage of an extraction countercurrent multistage scheme, the pulp is subjected to treatment with ultrasonic field of frequency 10 - 60 kHz for 3 to 15 minutes.

WO 02/20151 describes a method of performing a chemical reaction between a first material and a reagent, the reaction being carried out between the first material in particulate form and a liquid that comprises the reagent, one reaction product being a solid material, the particles of the first material being of such a size that formation of a surface layer of the said solid material suppresses the reaction, the method comprising a contact between the first material and the reagent in a plant, the plant comprising at least one reaction vessel with a multiplicity of ultrasonic transducers attached to a wall of the vessel so as to irradiate ultrasonic waves into the vessel, the vessel being large enough that each transducer irradiates into fluid at least 0.1 m thick, each transducer irradiating no more than 3 W/cm ² , and the transducers being sufficiently close to each other and the number of transducers being sufficiently high that the power dissipation within the vessel is at least 10 W/litre but no more than 200 W/litre, stirring the contents of the reaction vessel, and energizing the transducers.

The known methods do not ensure exposure of the treated material to ultrasonic intensity throughout the entire volume of the reactor which leads to a

reduction in the efficiency of material disintegration and the degree of extraction of precious components.

DESCRIPTION OF THE INVENTION

This invention refers to a method for metal leaching which ensures subjecting to ultrasonic intensity throughout the entire reactor volume and increase in the speed and the degree of extraction from the metal-containing materials in the metal phase.

According to the invention, a method for metal leaching comprises a contact of granulated metal-containing material with an aqueous solution of chemical reagents in a pipe reactor, the metal-containing material and the aqueous solution of chemical reagents being delivered to the pipe reactor from its bottom in a continuous direct flow. The resultant pulp from the metal- containing material and the aqueous solution of chemical reagents is passed through the pipe reactor from the bottom upwards, simultaneously being subjected to ultrasonic field treatment. The ultrasonic field is created by a multiplicity of ultrasonic wave sources, located in the pipe reactor in a helical line with an axis coinciding with the pipe reactor axis, and the said ultrasonic wave sources are in equal distances from each other, thus ensuring an average ultrasound specific volume power W/Q of 1 to 10 kW/m ³ . The pulp is passed through the pipe reactor with such a speed that ensures sufficient time for the material to contact the chemical reagents, being simultaneously under the action of the ultrasonic field for 2 to 8 minutes.

The number of the ultrasonic wave sources is between 3 and 40 depending on the pipe reactor height and diameter, the power capacity of the individual ultrasonic field sources, and the type of the metal-containing material to be processed.

The number of turns in the helical line is determined depending on the number of the ultrasonic wave sources. More than one ultrasonic wave sources can be located equidistantly on a turn.

In a preferred invention embodiment the processed metal-containing material is passed from below upwards through an ultrasonic field with an increasing frequency, the ultrasonic wave source attached to the bottom section of the pipe reactor being operating with a frequency of 15 kHz to 18 kHz, and the ultrasonic wave source attached to the top section of the pipe reactor being operating with a frequency of 30 IcHz to 40 IcHz.

The helical line pitch is between 1/4 and 1/6 of the diameter D of the reactor.

The diameter d of the helical line is 0.6 to 0.9 of the diameter D of the reactor which ensures a sufficient distance between the ultrasonic wave sources and the reactor walls, and prevents from wall erosion.

If necessary, the pulp, comprising a chemical reagent solution and metal- containing material particles, is homogenized by mixing through a mixer, mounted along the pipe reactor axis, the mixing element of the mixer being positioned underneath the bottom ultrasonic wave source.

The size of particles of the metal-containing material to be leached depends on the type of material, and most often is below 1.0-0.5 mm.

The term "Average ultrasound specific volume power W/Q" means the ultrasonic energy, created by all ultrasonic wave sources, relevant to a unit of pulp volume.

The method for metal leaching according to the invention has the following advantages: original location of the ultrasonic wave sources, i.e. in a helical line; and the usage of average ultrasound specific volume power within the specified range increases repeatedly the mass-exchange in the reactor volume, and prevents from formation of 'dead' zones wherein lack of ultrasonic intensity over the material can be observed. Thus the material is prevented from passivation in the reaction zone at the boundary of the solid/liquid phase. As a result, the speed of the chemical reaction increases, and the time that the processed material stays in the reactor significantly decreases at an increased degree of precious component extraction. On usage of an ultrasonic field with an increasing frequency a most efficient degree of extraction process activation is

achieved due to the occurrence of defects in the material crystal lattice. This leads to fine crushing of the particles, and also to removal of the particle surface layers, and to a continuous renewal of the reaction surface of the particles.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a schematic representation of an alternative of a pipe reactor embodiment in accordance with the invention.

Fig. 2 shows a schematic representation of a second alternative of a pipe reactor embodiment in accordance with the invention.

EXAMPLES OF INVENTION EMBODIMENTS Example 1. The method according to the invention was used for processing of flotation waste, containing 5 to 10 % metal sulphides, 50 to 55 % quartz and sericite, 30 % carbonates, 10 % bitumen, Cu 1.5, Fe 1.7 %, Zn 0.12 %, Pb 0.076 %.

The flotation waste is crushed to a particle size of 0.1 mm after which it is subjected to leaching in the pipe reactor 1, shown on Fig.l . Using a transportation means 7, the material is delivered to a collecting vessel 5, and using pipe 6 a solution of chemical reagent, being in this Example a 10 % sulphuric acid solution, is delivered to the same collecting vessel 5. The weight ratio of the flotation waste to the sulphuric acid solution in the pulp is 1 :1. Using a slime pump 4 and a pipeline 8, the resultant pulp of the flotation waste and the sulphuric acid solution is continuously fed into the reactor 1 from its bottom.

The reactor 1 has the following dimensions: height 3 m, diameter 2.5 m. The reactor 1 is equipped with three ultrasonic transducers 2, located in an imaginary helical line 3 with the following characteristics: diameter d 2.1 m, height h 1.5 m, pitch 0.5 m, and number of turns 3. The inclination angle of the helical line is determined experimentally depending on the reactor 1 dimensions, the number of turns, and the number of ultrasonic transducers. In this Example, there is one ultrasonic transducer 2 located at each turn, the imaginary centre of the irradiating surface of each transducer 2 laying on the helical line.

Each ultrasonic transducer 2 is connected to the relevant ultrasonic generator (not shown on the drawing), which is controlled separately. The ultrasonic transducers 2 operate with different frequencies, the one located at the bottom level operates with 15 kHz, the one at the middle level with 20 IcHz, and the one at the top level with 40 IcHz. The total power of the ultrasound in the reactor 1 is 21 IcW, and the average ultrasound specific volume power W/Q = 1.75 kW/m ³ .

The speed of pulp delivery ensures a downtime of about 5 minutes in the reactor 1 during which the material contacts the chemical reagents, and is processed through ultrasonic field. The processed pulp leaves reactor 1 via overflow pipe 10.

A sulphuric acid solution with concentration of copper ions of 10.9 - 12.0 g/1 is obtained upon separation of the liquid from the solid phase. The solid residue is washed, dewatered, and deposited or used for extraction of other precious components through other known methods.

Table 1 shows the results obtained.

The degree of copper extraction is 87.3 %.

In the other alternative of the invention embodiment, shown on Fig. 2, the reactor 1 is equipped with a mixer 11, mounted along the reactor 1 axis, the mixing element of the mixer 11 being positioned underneath the bottom ultrasonic transducer 2. All items from 1 to 10 are the same as in Fig. 1. Mixing the pulp which is fed from the reactor 1 bottom, results in higher homogeneity and in intensification of the chemical reaction occurrence.

Example 2. The method according to the invention was used for processing of flotation waste, containing 5 to 10 % metal sulphides, 50 to 60 % quartz, up to 27 % carbonates; Cu 0.15, Fe 10-13 %, Zn 0.07 %, Ti 0.63 %.

The flotation waste is crushed to a particle size of 0.1 mm after which it is subjected to leaching. The obtained material is processed in a pipe reactor with the following dimensions: height 3 m, diameter 2.5 m. The reactor is equipped with nine ultrasonic transducers, located in a helical line with the following characteristics: diameter d 2.1.m, height h 1.5 m, pitch 0.5 m, number of turns 3, three ultrasonic transducers being located at each turn. The ultrasonic transducers operate with different frequencies (from the bottom to the top level of the reactor): 15 IcHz; 18 IcHz; 20 IcHz; 20 IcHz; 25 IcHz; 30 IcHz; 30 kHz; 35 IcHz; 40

IcHz. The average ultrasound specific volume power W/Q in this Example is 5.3 kW/m ³ .

The chemical reagent used for extraction of the precious components is a 10 % solution of sulphuric acid. The processed material and the sulphuric acid solution are fed in a direct flow from the bottom upwards and pass through ultrasonic field with increasing frequency. The speed of material delivery ensures a downtime of about 4 minutes in the reactor.

A sulphuric acid solution with concentration of copper ions of 0.76 - 0.82 g/1 is obtained upon separation of the liquid from the solid phase. The solid residue is washed, dewatered, and deposited or used for extraction of other precious components through other known methods. Table 2 shows the results obtained.

Table 2

The degree of copper extraction is in average 79 - 81 %.