EA039147B1 - Process, unit and precious metal extraction unit for improving the yield for precious metal extraction in a sorption-leaching process - Google Patents

Abstract

The invention relates to a process, a unit and a gold and/or silver extraction unit for improving the yield in a sorption-leaching process (10) for extracting precious metals, in which the efficiency of the process is limited in particular by the organic carbon and/or sulphide sulphur content in the raw material, such that quantitative residual amounts of precious metals remain in the sorption sludges produced during the sorption-leaching process (10); involving the steps of processing of the sorption sludges in preparation for an oxidising roasting step (80), wherein the sorption sludges are dewatered (18), dried (24) and granulated (26); oxidising roasting (80) of said processed sorption sludges; and feeding of the roasted sorption sludges to a further leaching or sorption-leaching process (10).

Description

The present invention relates to a method for increasing recovery in precious metal mining, in particular gold or silver mining, in a sorption leaching process, in which the efficiency of the process is limited, in particular, by the content of organic carbon and/or sulfide sulfur present in the feed, so that in the sorption tailings formed in the process of sorption leaching, the residual fractions of the noble metal are in significant concentrations. In addition, the method is especially suitable for gold-bearing ores, in which gold (mainly in the form of finely dispersed inclusions) in addition to sulfide minerals (for example, pyrite) is in association with arsenic-containing minerals (for example, arsenopyrite), and when the organic carbon present in the ores significantly negatively affects the extraction of gold from ores.

Although the present process is currently of commercial interest primarily for the extraction of gold, it is also fundamentally suitable for the extraction of silver or for the simultaneous recovery of gold and silver. The silver alternative will not be mentioned below every time.

In addition, the present invention relates to a method plant and a gold mining plant.

Sorptive leaching methods based on the principle of carbon in leaching solution or CIL are relatively common in gold mining. In addition, the so-called CIP, RIP, RIL methods are also used. In the CIL process, leaching and sorption occur simultaneously; in contrast to the CIP process, in which leaching occurs first and then adsorption on activated carbon. Adsorption can (more rarely) also be carried out on an ion exchange resin (RIP, RIL processes). As used below, the term sorption leaching process encompasses all of the above or well-known process variations.

The processes of leaching and sorption are based on the oxidation of gold finely disseminated in the rock with air oxygen and its dissolution in an alkaline aqueous solution containing cyanide ions.

Ores are usually crushed, crushed and sent to flotation enrichment. The flotation concentrate pulp is thickened and transported to the so-called biological leaching. During the biological leaching process, most of the arsenic and sulfide sulfur is oxidized and dissolved in the form of sulfates and arsenates. Gold particles trapped in arsenic- and sulfide-containing minerals are released. The slurry after biological leaching is thickened and fed into a countercurrent decantation wash in order to separate the aqueous phase and wash out the solid residue. The liquid phase is then neutralized, whereby arsenic precipitates in the form of iron arsenates (scorodite) and sulfates in the form of gypsum. The solid residue is also neutralized and sent to sorption leaching. During sorption leaching, the gold released by the biological leaching is dissolved and adsorbed on activated carbon. Tailings from sorption leaching are transferred for further processing.

Thus, sorption tailings or sorption sludges are formed in this process. This is a waste of the sorption leaching process in the production of primary gold from concentrates. These wastes, which are sent to storage at other plants, may still contain significant amounts of gold. This gold is not recovered in the process of leaching and sorption by traditional methods. The reasons for this are, first of all, the content of organic carbon and sulfide sulfur in the source material.

The term organic carbon should be used subsequently to distinguish it from activated carbon (with a much larger particle size) used in the sorption process.

Organic carbonaceous substances in particular are the cause of the so-called pregrobbing effect - a spontaneous and irreversible process of transition (adsorption) of dissolved gold (in the form of a cyano complex) to ore components. The sorption activity of carbonaceous matter leads to the loss of gold with the solid phase of sorption tailings.

The patent US 4919715 A is known from the state of the art.

The object of the invention is to significantly improve the recovery of gold in known sorption leaching processes by processing sorption sludges and to carry out the processes required for this in an efficient and environmentally compatible manner.

The solution of the above problem is achieved using a method having the features of claim 1, using a plant with features of claim 12 and using a gold and/or silver mining unit according to claim 14.

Preferred embodiments of the invention are described in the relevant claims.

According to the invention, the following steps are proposed:

a) preparation of sorption tails for processing by oxidative roasting (80), in which sorption tails are subjected to dehydration (18), drying (24) and granulation (26),

b) oxidative roasting (80) of prepared sorption tailings, and

c) preparing the calcined product and feeding it into the subsequent sorption leaching process.

- 1 039147

Numerous studies using various methods in the context of the present invention have shown that the oxidative roasting method provides the highest recovery of gold from sorption tailings.

During the roasting process, sulfur sulfide or iron sulfide, in particular pyrite (typical pyrite content in the starting material is about 3.8%), as well as organic carbon, are transferred into the gas phase according to the following reaction equations and thus removed to the maximum extent possible:

3FeS ₂ + 8О ₂ = Fe ₃ O ₄ + 6SO ₂

3FeS + 5О ₂ = Fe ₃ O ₄ + 3SO ₂

4Fe ₃ O ₄ + O ₂ \u003d 6Fe ₂ O ₃

C + O ₂ = CO ₂

Due to the oxidation of sulfides during the roasting process, on the one hand, gold (usually finely dispersed) associated with sulfide minerals is released. On the other hand, due to the conversion of sulfides, a porous structure is formed that is easily accessible to cyanide solutions, which, in turn, improves the leaching of gold. In addition, this reduces the increased consumption of reagents during cyanidation, which is known to be associated with the presence of sulfide minerals.

Arsenic sulfide compounds are also oxidized during oxidative roasting, with the same effects as described above for sulfide sulfur:

12FeAsS + 29О ₂ = 4Fe ₃ O ₄ + 6As ₂ O ₃ + 12SO ₂

By oxidizing the organic carbonaceous matter, which is the cause of the adsorption activity of the material, the effect of preg-robbing during the subsequent leaching is suppressed, so that the gold associated with the organic carbon can be recovered.

Exhaust gases from the kiln are dedusted, cooled and cleaned of harmful substances to the maximum extent possible in a multi-stage gas cleaning system.

The calcined product is cooled, pulped with water and sent to a sorption leaching process where substantial high amounts of gold are adsorbed onto the activated carbon and can be recovered by known methods.

The roasting process is preferably carried out in a CFB (Circulating Fluidized Bed Furnace) because it provides the best mass and heat transfer, high chemical reaction rates and accurate temperature control. Thus, the oxidative roasting in step b) preferably takes place in a circulating or stationary fluidized bed process.

The stationary fluidized bed method or fluidized bed calcination has the advantage that the residence time of the calcined product in the process can be controlled more precisely than in the circulating fluidized bed process.

In particular, within the framework of a preferred embodiment of the invention, the stationary fluidized bed apparatus can be connected in series after firing in the CFB furnace in order to ensure the minimum required firing time.

Proposed in stage b) oxidative roasting is preferably carried out in the temperature range from 450 to 750°C, most preferably in the range from 500 to 700°C.

In addition, the residence time of the sorption tailings in the stage of oxidative roasting is preferably chosen so that the residual content of sulfide sulfur and/or organic carbon is reduced to values of less than 0.75%, preferably less than 0.5%, most preferably less than 0.1%.

The optimum residence time of the material using this method lies in the range of 20-180 minutes, preferably about 30-90 minutes, especially preferably 40-60 minutes. Optimum residence time in the calcination process is understood as the necessary processing time to achieve the above-mentioned residual concentrations of organic carbon, as well as sulfide sulfur.

The optimum air flow velocity in an empty pipe in a CFB furnace according to this method lies in the range of 2-5 m/s.

As preparation for the oxidative roasting process in step a), the sorption tails are dehydrated, dried and granulated. In these steps, the raw material is converted into a material with a uniform particle size, which is optimal for a reproducible firing process in the preferred CFB furnace.

Sorption sludge is a finely dispersed material and cannot be processed in the kiln in its original form (high dust emission, insufficient and uneven residence time in the kiln).

Uniform optimal size distribution of the sludge particles is achieved through the granulation process. In this case, thin solid particles due to wetting with a liquid under the action of capillary as well as adhesive forces bind to each other. In order to achieve this bond, the parent substances must move in a direction opposite to each other.

Particularly when granulating in intensive mixers with fast rotating

- 2 039147 mixing tools form relatively fine granules of high density, which are suitable for the subsequent firing process in the predominantly used CFB furnace. In order to ensure satisfactory mechanical and thermal strength, binders, preferably bentonite, must be dosed into the granulation process.

In addition, other inorganic and organic binders such as burnt lime or lignosulfonate can be used. The optimization of the volumes of dosed binders is carried out after analyzing the mass flows of the subsequent firing process (primarily the removal of dust from the kiln).

In order to obtain a suitable granular material, other incremental or wet granulation methods can be used, such as granulation in mixers as well as plate granulators, provided that the subsequent firing process in the CFB kiln runs optimally, i.e. with the lowest possible dust emission and the achievement of optimal residual concentrations of organic carbon and sulfide sulfur in the roasting products.

In principle, the term granulation can also include compaction methods such as, for example, briquetting.

The preferred particle sizes of the granular material are in the range of 80-90% below 2 mm (d50 value in the range of 800-1000 µm). The granular material can also be coarser or finer, provided that the subsequent firing process in the CFB kiln proceeds optimally.

After dewatering, a washing of the filter cake is preferably carried out in order to flush out the aqueous phase cyanides that would otherwise enter the off-gas, especially during drying, resulting in complex off-gas treatment.

The cyanide-containing liquid phase obtained from washing can be returned to the sorption leaching process in the same way as the cyanide-containing wastewater from the previous dewatering stage, which reduces the need for cyanide and the impact of cyanide on the environment.

In order to feed the calcined sorption tailings to the subsequent sorption leaching stage in step c), the cinder is preferably cooled and mixed with water. Due to the very good mixing of the solids inside the predominantly used CFG oven, attrition and destruction of the granules occurs. However, in order for the subsequent cyanidation process to work efficiently (ie, in order for the gold recovery to be high), a certain uniform particle size distribution of the solids must be achieved. Therefore, depending on the desired particle size distribution for the subsequent sorption leaching process, it may also be appropriate to further grind the cinder in a mill.

The pre-treatment of the material in the mill additionally leads to the fact that, due to the mechanical action, the surfaces of the particles are released and thus become available for leaching.

The leaching and sorption of the roasted sorption tailings preferably takes place in a separate sorption leaching process.

Off-gases containing harmful substances generated during roasting are preferably fed into a multi-stage off-gas purification process. In this case, for example, dust collection can be carried out using cyclones (coarse dust) and dry electrostatic precipitators (fine dust), and the precipitated gold-containing dust can be again fed to granulation or directly to the leaching and sorption process. After the dry electrostatic precipitator, several wet cleaning stages and, if necessary, a wet electrostatic precipitator can be connected.

The dust from the kiln gas dedusting system is cooled and preferably sent to granulation and partly directly to sorption leaching. Due to the addition of dust for granulation, the required humidity value can be adjusted.

After removing the dust, the flue gases are cooled down to about 80°C so that the arsenic trioxide they contain can condense and be washed out.

Wastewater containing arsenic is returned to the biological leaching process, where arsenic compounds are oxidized so that arsenic can be precipitated as iron arsenate in a subsequent neutralization step. Residual arsenic and dust are separated in wet electrostatic precipitators.

Subsequently, the flue gas is desulfurized, for example in a scrubber, by dosing a suspension of milk of lime.

The calcined product is cooled, pulped with water, crushed and sent to the subsequent sorption leaching process, due to which a much larger amount of gold can be extracted from the raw material on activated carbon than with other known processes.

The invention is explained in more detail and exemplarily in the drawings. The drawings show:

fig. 1 is a schematic block diagram of the pre-treatment of sorption tailings;

fig. 2 is a more detailed block diagram of the general sequence of process steps in accordance with the invention;

- 3 039147 fig. 3 is a block diagram of oxidative roasting and subsequent process steps.

The method presented below should be understood as an example only. Where appropriate, one skilled in the art may omit some steps, add additional process steps, or perform the steps in a different order.

In FIG. 1, the sorption leaching process is designated by the general reference number 10. With regard to the specific implementation of this process, reference is made to the literature. The source material (12) is supplied to the sorption process (10).

The product of step 10 is an enriched concentrate in which gold cyanide is bound to activated carbon. In further steps 16, these bound gold cyanide complexes are isolated and removed from the activated charcoal.

Further, sorption sludges are formed in process 10, which are usually waste, but often contain a significant amount of gold, especially if the leaching/sorption process has a negative impact on the efficiency of high contents of organic carbonaceous matter and/or sulfide sulfur in the source material. Often the content of gold remaining in the sorption tailings can be several times higher than 5% of the total amount of gold in the raw material.

Therefore, according to FIG. 1, the sorption sludges (or at least a portion thereof) are prepared for the roasting process in a circulating fluidized bed furnace. For this purpose, it is advantageous for the sludge to be as uniform as possible in terms of composition, moisture content, shape and surface and particle sizes.

To do this, the sorption sludge is first dehydrated at stage 18, and then pressed to obtain a filter cake (stage 20), which is washed, stored in the filter cake intermediate storage (stage 22) and dried in drum dryers at stage 24.

Of course, it is also possible to omit intermediate storage or to carry out intermediate storage of the product after drying.

The intermediate warehouse serves as a store for the period of repair at subsequent installations or for averaging the source material.

In the next step 26, the dried filter cake is produced into a granular material with the most uniform shape and optimal particle size for the fluidized bed furnace process. The mechanical and thermal stability of the pellets can be ensured by the controlled addition of a binder, preferably bentonite.

This granular material is then sent to oxidative calcination at step 28, which is illustrated schematically in FIG. 3.

In FIG. 2 shows a block diagram of the general process flow in accordance with the invention, including the sorption leach process and the biological leach step. The feed ore (100) is crushed and ground in step 102. In step 104, flotation occurs with a thickening step, the respective tailings (106) are treated separately.

The concentrate (108) is then fed to the so-called bioleaching stage 110. In stage 114, thickening is carried out with countercurrent decantation washing of the solids. The resulting liquid phase (116) contains relatively high concentrations of arsenic. In the neutralization step (118), this arsenic is precipitated in the form of iron arsenate.

The bioleachate (120) is subjected to neutralization and sorption leaching using cyanide (step 122), and activated carbon (124) is used to recover the gold.

In this case, sorption tails (126) are formed, in which significant gold contents may still remain.

For this reason, the sorption tails (126) are prepared for the roasting process, in that they are first dehydrated (stage 128), and the resulting liquid cyanide-containing phase according to stage 130 can be returned to the sorption leaching process.

The filter cake (142) obtained from the dewatering step (128) is then washed (step 132), which has proven to be a very effective measure to reduce its cyanide content; in this way, it is subsequently possible to either omit the more costly off-gas purification steps or simplify them. The cyanide-containing effluent generated during filter cake washing may also be returned to the sorption leaching process (step 134). The washed filter cakes (142) are placed in temporary storage as needed (step 144).

The filter cake is then dried at stage 136. The exhaust gas of the dryers (138) is dedusted (stage 140), and this dust can be fed to subsequent granulation (146). Next, at step 146, granulation is carried out to obtain the optimal grain size for the subsequent firing process (step 150), in which, for example, 80-90% of the particles of the granular material may have particle sizes of less than 2 mm, or the d50 value for the granular material may be in the range from 800 to 1000 microns.

Roasting (step 150) is preferably carried out by means of a circulating fluidized bed process in which off-gases (152) are dedusted in step 154 and the dust (156) is returned to granulation (146). Off-gases from the dedusting process (162)

- 4 039147 at stage 154, are purified from arsenic at stage 164, and wastewater containing arsenic (112) can again be sent to biological leaching (110).

The arsenic-free effluent gas is then desulfurized at step 170 and may be discharged to the environment at step 180, whereby the desulphurization produces landfillable gypsum (178).

The resulting calcination (150) calcine (158) is first cooled in step 160, crushed in step 166, and then subjected to a second neutralization/sorption leaching process in step 172, which is preferably a separate process from step 122.

Also here, gold recovery can ultimately be accomplished with activated carbon (step 174) or with one of the other leaching and sorption options described above.

Sorption tailings 176 from the second sorption leaching process are finally sent to landfill.

In FIG. 3, the circulating fluidized bed furnace is indicated at 50. The circulation of material in this fluidized bed furnace 50 is effected by means of a series-connected cyclone 52 and an air lock 56 located downstream. To do this, preheated compressed air is supplied to the furnace 50 or the air lock 56 at points 58 and 66 (the bottom of the air lock). The loading of granular sorption tailings takes place at point 64 between the air lock 56 and the material return pipeline to the fluidized bed furnace 50. The resulting exhaust gases are removed at point 54 and subjected to multi-stage purification (not shown in detail), while the settled dust can be returned to the granulation process or directly directed to the process of leaching and sorption (also not shown in detail).

The material is unloaded from the circulation circuit in the fluidized bed from the pneumatic lock 56 with the supply to the fluidized bed afterburner 68. A small part of the product settles on the bottom of the fluidized bed furnace (50) and is regularly removed from there through point 62, and periodically fed in portions manually for further processing, preferably at a point before the mill 74 mentioned below.

The actual firing process takes place continuously at a temperature of 450 to 750° C., preferably 500 to 700° C., maintained by power supply (if necessary) from a natural gas burner (60) (an additional existing starter burner is not shown in Fig. 3).

The amount of loaded and unloaded materials is set in such a way that the fired material stays in the furnace on average for a specified minimum time.

To ensure the minimum actual holding time (and not just the average), the calcined product is continuously and in a controlled manner sent to the afterburner KS 68, where the calcination process continues for a specified period of time with the supply of hot compressed air in a specified temperature range.

Thus, in general, oxidative roasting of sorption sludge occurs in the apparatuses of the section designated by number 80.

In the further course of the process, the calcined material is sent to the next pneumolock 70 and to the cinder cooler 72. Further, in the mill 74 with one or more hydrocyclones located downstream (the latter are not shown), the optimal distribution of the particle size of the calcined product for the subsequent sorption leaching process is ensured.

The crushed calcine is further sent in the form of a suspension (76) to a repeated or subsequent sorption leaching process (78), and the necessary pulping to obtain a suspension 76 is carried out before grinding and before hydrocyclone.

Below is a more detailed explanation of the invention using examples.

Example 1 (Granulation).

A sample of sorption tailings was dehydrated and dried (the residual moisture content was about 5%). Approximately 30 kg of dried sludge was loaded into a large-scale intensive laboratory mixer. Next, 8.2 kg of water was dosed into the mixer. From the dried material and water, a plastic mass was made, similar to a partially dried filter cake. Approximately 1.4 kg (3% dry weight) of bentonite was then added to the resulting mass, as well as an additional 20 kg of dry material. Subsequently, the granulation process was carried out in an intensive mixer. The moisture content of the granulation was about 18%, the duration of the granulation was approx. 4 min. The particle sizes of the resulting granular material were 80-90% below 2 mm.

Example 2

A sample of sorption tailings (sorption leach I) was dehydrated, dried and granulated as described in Example 1, and then fired in a CFB pilot furnace at various temperatures. Air was used as the fluidizing medium. Subsequently, the cinder was crushed (80% below 0.044 mm) and sent to sorption leaching (II). Activated carbon was used as a sorbent. Also fine dust from the hot filter was subjected to sorption leaching (II).

The table below shows the thus obtained residual Au content in the tailings of sorption leaching (II) carried out under the same process conditions, the initial Au content in the cinder and dust samples taken in the roasting experiments at temperatures of 600 and 650°C, as well as the calculated values gold recovery rate during sorption leaching (II).

As can be seen from the table below, by processing sorption tailings (waste that usually has to be disposed of), it is possible to recover approximately 70% of Au additionally.

Try Products Gold content, g/t Gold recovery, % Firing temperature 600°C cinder Extraction of gold to coal 71.31 Cyanidation tailings 1.03 28.69 Sample before cyanidation 3.59 100.00 Firing temperature 600°C dust Extraction of gold to coal - 54.52 Cyanidation tailings 1.86 45.48 Sample before cyanidation 4.09 100.00 Firing temperature 650°C cinder Extraction of gold to coal - 72.49 Cyanidation tailings 1.07 27.51 Sample before cyanidation 3.89 100.00 Firing temperature 650°C dust Extraction of gold to coal 68.58 Cyanidation tailings 1.48 31.42 Sample before cyanidation 4.71 100.00

CLAIM

Claims (13)

1. A method for increasing recovery in the extraction of gold and/or silver in a sorption leaching process (10), in which the efficiency of the process is limited by the content of organic carbon and/or sulfide sulfur present in the feedstock, so that significant residual residues remain in the sorption tailings. gold and/or silver content, with the following stages: a) processing of sorption tailings as preparation for oxidative roasting (80) by dewatering (18), drying (24) and pelletizing (26), b) oxidative roasting (80) of the prepared sorption sludge, and c) preparation of roasted sorption tailings and feeding them to the subsequent sorption leaching process. 2. Method according to claim 1, characterized in that the oxidative roasting (80) in step b) takes place in a circulating fluidized bed process. 3. Process according to one of claims 1 or 2, characterized in that the oxidative roasting (80) in step b) takes place at temperatures between 450 and 750°C. 4. The method according to one of claims 1 to 3, characterized in that the residence time of the sorption tails in the oxidative roasting (80) is chosen so that the residual content of sulfide and/or organic carbon is reduced to less than 0.75%, preferably less than than 0.1%, and the residence time is at the level of 20-180 minutes, preferably 30-90 minutes and especially preferably at the level of 40-60 minutes. 5. Method according to one of claims 1 to 4, characterized in that the particle size of the granular material obtained after the granulation step (26) is 80-90% below 2 mm and/or the particle size of the granular material is indicator d50 in the range of 800-1000 microns. 6. Method according to one of claims 2 to 5, characterized in that after the oxidative roasting in the circulating fluidized bed process, an afterburning process is carried out in a stationary fluidized bed (68). 7. The method according to claim 6, characterized in that after dehydration, the filter cake is washed in order to wash the aqueous phase from cyanides, and the cyanide-containing liquid phase obtained during washing and / or wastewater formed during dehydration is returned to the process sorption leaching. 8. The method according to one of claims 1 to 7, characterized in that before feeding the calcined sorption tailings to the stage of subsequent sorption leaching, the cinder is cooled, optionally crushed and pulped with water in stage c). 9. The method according to one of claims 1 to 8, characterized in that the exhaust gases formed during oxidative roasting (80) are sent to a multi-stage purification stage (54), including dedusting - 6 039147 10. The method according to claim 9, characterized in that the dust from the dedusting stage of the roasting gases is sent to granulation to control the required moisture content and / or directly to the subsequent sorption leaching. 11. The method according to claim 9 or 10, characterized in that, after removing the dust, the flue gases are cooled in such a way that the arsenic trioxide contained in the flue gas is condensed and washed out, and the arsenic-containing wastewater resulting from this washing is sent back to the biological process. leaching, so that the arsenic is oxidized during the biological leaching process and can be precipitated in the form of iron arsenate in a subsequent neutralization step. 12. Installation for the extraction of gold and silver for implementing the method according to any one of claims 1-11, containing: dehydration unit for dehydration of sorption tailings; a drying unit for drying dehydrated sorption tailings; granulation unit for granulation of dried sorption tailings; a roaster (80) for oxidative roasting of granular sorption tailings; and a sorption leach unit, which is supplied with calcined and suitably prepared sorption tailings in order to recover a significant proportion of the gold and/or silver. 13. An installation for the extraction of gold and/or silver, including: the first stage of the sorption leaching process with the stage of biological leaching and the installation according to paragraph 12.