RU2789630C1 - Substandard gold coal sorbent recycling method - Google Patents

Abstract

FIELD: gold-mining industry.

SUBSTANCE: invention relates to gold-mining industry, in particular to recycling of substandard gold coal sorbent separated from a gold-processing plant operating procedure. Method includes performance of the following operations that are interrelated in terms of operating procedures: desorption, saturated solution filtration, saturated solution sorption on conditioned regenerated coal. After the sorption the saturated coal is sent for processing to extract gold, and the depleted solution is returned for desorption performance forming a closed cycle of solution development.

EFFECT: invention expands the range of technical means for processing substandard coal sorbent separated from the gold-processing plant operating procedure.

4 cl, 2 tbl, 4 dwg

Description

The field of technology to which the invention belongs

The invention relates to the gold mining industry, in particular to the processing of substandard gold-containing coal sorbent (NUS), isolated from the technological process of gold recovery plants (GIF).

State of the art

In practice, many processes are known that use the process of direct elution of gold from activated carbon.

A known method for extracting gold and silver from activated carbon (invention No. RU 2064513, publ. 27.07.1996), including the treatment of saturated coal with an alkaline solution of sodium cyanide and subsequent desorption with hot water in an autoclave, the desorption is carried out at 165-175°C.

A method is known for extracting precious metals from saturated activated carbon (invention No. RU 2044085, publ. 09/20/1995), including treatment of saturated coal with an alkaline solution of sodium cyanide and subsequent desorption with hot water in an autoclave with 7-10 volumes of eluent per volume of coal, at a desorption temperature of 165 -175°C.

The disadvantages of these technical solutions is that they are not very effective in the processing of coal fines, since the use of an autoclave leads to the washing out of fine particles from the desorber.

There is a known method for extracting gold and silver from activated carbon by leaching and electrolysis (Zadra J. B. A process for the recovery of gold from activated carbon by leaching and electrolysis / / U. S. Bureau of Mines Reports of Investigations, 4672. - 1950, April. - P. 4672 –4677.). This method is based on the principle of operation of a sorption column, in which, upon heating and supplying an alkaline cyanide solution, the process switches to the desorption mode, after which gold is eluted from the sorbent and removed from the column in the form of a cyanide complex. The solution is then sent for electrolysis.

The disadvantage of this method is to obtain insufficiently rich eluates for electrolysis, since during electrolysis its efficiency depends on energy consumption, and productivity is limited by the size of the electrolysis baths, as a result of which, at a low concentration of gold, a large amount of solution has to be processed over a longer time.

As the closest analogue, taken as a prototype, a processing method was chosen, including sintering of substandard gold-containing coal sorbent in the form of waste to obtain gold-containing agglomerates, which are crushed and sent for leaching with a cyanide solution to obtain a solution saturated with gold, sorption of a saturated solution on activated carbon, including conditioned regenerated coal, after which the saturated coal is sent for processing to recover gold, and the depleted solution is returned to leaching with the formation of a closed solution movement cycle (CN 104357664 B, 22.02.2017 (available online: https://worldwide.espacenet.com/publicationDetails /biblio?DB=EPODOC&II=0&ND=3&adjacent=true&locale=en_EP&FT=D&date=20150218&CC=CN&NR=104357664A&KC=A).

The disadvantages of this method are the multi-stage process, a large number of apparatuses (furnaces, mills, main and additional tank equipment), the need for a dust collection system, the need for deeper heat treatment of the substandard sorbent with a change in its structure (ashing, sintering), the supposedly higher capital costs for organizing site and high operating costs for its maintenance.

The technical problem is to create an optimal method for processing substandard coal sorbent with simplicity of instrumentation and achieving maximum gold recovery.

The technical result of the invention is the expansion of the arsenal of technical means that allow processing substandard coal sorbent isolated from the technological process of gold recovery factories.

The technical problem is solved by a method for processing substandard gold-containing coal sorbent includes a desorption operation connected by a technological process, filtration of a saturated solution, sorption of a saturated solution on conditioned regenerated coal, after which the saturated coal is sent for processing in order to extract gold, and the depleted solution is returned to the desorption operation, forming a closed solution motion cycle.

The extraction of gold from finely dispersed off-grade coal sorbent (NSS) is an important process for gold mining companies, since different batches of NSS can contain from 0.1 to 5 kg/t of gold.

The main equipment of the gold processing plant for desorption-electrolysis, which is usually used to work with coarser conditioned coal in the autoclave mode and is under a pressure of 5-6 atm. desorber under pressure, which leads to clogging of existing filter systems, stopping circulation, and contamination of the cathode deposit. The passage of the desorption process at atmospheric pressure, a temperature below the boiling point and at a certain speed creates the necessary conditions for conducting the desorption process without washing out the material. According to the invention, the desorption process is combined with the parallel sorption of the material onto conditioned coal. After the end of the desorption process, saturated conditioned coal can be involved in the main desorption process of the gold processing plant in the normal mode.

In the proposed method, the desorption process proceeds at a solution circulation rate through the NUS layer within 0.8-1.2 solution volume per 1 coal volume per hour (0.8-1.2 m ³ /hour: 1 m ³ ) and at atmospheric pressure, while there is no washing out of the fine fraction of NUS from the desorption column, as when working under pressure in a closed autoclave. Under pressure, the flow of fluid movement becomes turbulent even at low flow rates, and the resulting turbulence lifts small NUS particles, and when operating at atmospheric pressure, the flow movement is in a calmer laminar regime. In addition, the instrumental simplicity of operating at atmospheric pressure significantly reduces the cost of equipment and the requirements for personnel in terms of safety. The use of a solution circulation rate (0.8-1.2 volume of solution per 1 volume of coal per hour (0.8-1.2 m ³ /h: 1 m ³ ) ensures that there is no effect of washing out fine particles of NUS. To further eliminate the possibility of washing out fine particles of NUS, a control filter is used at the outlet of the desorption column.The desorption temperature is maintained below the boiling point at a level of 85-90 ° C and is achieved through the use of a heating jacket, which is an isolated environment around the reactor with a heated coolant, as well as the use of thermal insulation of the column. The optimum temperature of the desorption process is 85-90 ° C. When the desorption temperature is set below 80 ° C, the duration of desorption increases, and the concentration of gold in the saturated solution at the outlet of the column decreases. When the desorption temperature is set above 90-95 ° C, there is a risk of solution boiling which will wash out the NSS from the desorption column. solution, for example, solutions of the following compositions can be used:

- cyanide-alkaline (NaCN not less than 15 g/l, NaOH not less than 20 g/l);

- alkaline (NaOH not less than 20 g/l);

- alkali cyanide with other concentrations,

- cyanide-alkaline solutions with the addition of organic substances (eg with methanol).

These desorption regimes are characterized by a long process time (up to 3 days depending on the initial gold content at NSS) and a low gold content in the solution after desorption, so it is not advisable to use electrolysis for gold deposition. In the claimed method, it is proposed to use cooling of the desorption solution and redeposition of gold in a sorption column according to the CIC type - (Carbon In Columns (the solution is supplied from the bottom of the column through a fixed layer of carbon sorbent)), and the de-gold solution is sent back to the desorption process, due to which a closed cycle of movement is realized alkaline cyanide solution. When implementing this method of NUS processing, the processes of desorption and sorption are carried out in parallel.

The proposed method makes it possible to obtain a low residual gold content of <50 g/t per NSS, and the gold content on standard coal in the sorption column can be obtained higher than on the original NSS before desorption by varying the amount of loading. The proposed method makes it possible to process NUS with a low gold content, which is inexpedient to be processed, using methods that use joint agitation of standard and substandard coal sorbent in an alkaline cyanide medium. The proposed method allows the use of a simpler instrumentation compared to pyrometallurgical methods, which require roasting in special furnaces and under certain conditions, followed by hydrometallurgical extraction of gold from the cinder. The proposed method is recommended for implementation directly at the gold processing plant where NUS is formed and saturated coal is processed.

The use of this method makes it possible to carry out the process of processing NUS without changing the main technological scheme of the gold mill due to the independent process of processing NUS and the return of conditioned coal with redeposited gold to the existing technological process of the gold mill.

The scheme of implementation of the claimed invention is shown in Fig. 1

To implement the claimed method, a device is proposed that consists of a gold desorption column into which NUS is loaded. The desorption column has a heating jacket, thermal insulation and an outlet filter. The device has a saturated solution tank, where the solution is accumulated and cooled to ambient temperature (for faster cooling of the solution, it is recommended to use a cooling circuit with recycled water from the mill). Also, the device consists of a sorption column for gold reprecipitation, a depleted solution tank, pipelines connecting all elements according to the scheme through which the solution moves, pumps that feed the sorption column with a solution from a saturated solution tank and a desorption column with a solution from a depleted solution tank.

Implementation of the method

The claimed method is carried out as follows: substandard gold-containing coal sorbent (NUS) is loaded into the desorption column through the top of the desorption column (loading hopper), then the desorption solution is supplied using a pump (sodium cyanide 15 g/l, sodium hydroxide 20 g/l, or solution of a different composition) and in parallel the heating of the column begins, for example, using a heating jacket, to a temperature below the boiling point of water (85-90°C). The solution is fed from the bottom of the column. The optimal flow rate of the solution in the column is set in the proportion of 0.8-1.2 volume of solution per 1 volume of coal per hour (0.8-1.2 m³ / hour: 1 m³). The time of the process of extracting gold from NUS varies from 1 to 4 days and depends both on the stability of the regime parameters and on the initial grade at NUS, the higher the initial grade, the more time is required for maximum gold recovery. Further, the saturated solution leaving the column passes through the control filter through the overflow and then flows through the pipeline into the receiving tank (saturated solution tank) where it is cooled to 20-30 °C (for faster cooling, it is recommended to use a cooling circuit in the saturated solution collection tank with circulating water of the mill or use a cooling jacket for the sorption column). The depleted NUS is discharged from the column at the end of the cycle. The criterion for the end of the cycle is the absence of gold in the solution after desorption, i.e. its content is less than the detection limit <0.10 mg/l, while the extraction from the NUS is considered to be the maximum possible. During desorption, washing out of small NUS particles from the column does not occur due to the solution flow rate of 0.8-1.2 solution volume per 1 volume of coal per hour (0.8-1.2 m³/h: 1 m³) and the presence of a control filter . Further, the saturated solution is pumped through the pipeline from the saturated solution tank to the sorption column, into which the conditioned regenerated coal from the main process of the gold processing plant (after the thermal reactivation operation) is preliminarily loaded, on which gold is deposited from the saturated solution due to the physicochemical mechanism of interaction of the cyanide complex gold and active surface of coal. The temperature in the sorption column should be close to the temperature of the working zone of 15-30 °C to suppress desorption processes, which is achieved by natural cooling of the solution after desorption or forced, if necessary, by using the cooling jacket of the sorption column. If the sorption temperature is set to less than 15 °C, the efficiency of gold sorption on coal will decrease due to the slowdown of the physicochemical sorption processes. If the sorption temperature is set to more than 30 °C, then the efficiency of sorption will also decrease due to the occurrence of a desorption process that competes with the sorption process. Further, after sorption, the depleted solution overflows through the drain pipeline into the tank for the depleted solution, from where it is pumped through the pipeline back to the desorption column and thus the solution moves in a closed cycle. Saturated coal is also unloaded from the sorption column at the end of the desorption cycle with NUS, it is also possible to reuse saturated coal until gold is found in a depleted solution at the outlet of the sorption column, thereby achieving maximum saturation of conditioned coal with gold. If necessary, the level of the solution in the intermediate tanks is replenished with water, the concentration of alkali and sodium cyanide is maintained by adding the necessary reagents (eg NaOH, NaCN) to the circulating solution. The efficiency of the process is controlled by periodic determination of the gold content in the liquid phase at the outlet of the desorption column and at the outlet of the sorption column. The process goes on continuously until it is completed. The process is considered completed when, at the exit from the desorption column, the gold content in the solution is below the limit of analytical determination, after which the circulation of the solution is stopped, the NUS in the desorption column is washed from alkali, sodium cyanide and other desorbing reagents with clean / process water, after which the NUS is unloaded from the column, while taking a control sample of depleted NUS for the analytical determination of gold, the result is compared with the original content and the recovery is calculated. In turn, saturated conditioned coal is also washed from desorbing reagents and removed from the sorption column, an analytical determination of the gold content on coal is carried out, and then the coal is sent for processing, for example, to the process of the main desorption of the gold processing plant. Washing solutions of sorption and desorption columns are sent to the site of sorption or neutralization of the gold processing plant.

Ultimately, the washing solutions of the desorption and sorption columns are sent for neutralization and disposal, the depleted NUS is sent for disposal, and the saturated conditioned coal is sent for further processing.

Table 1. Regime parameters of the process

Parameter Unit ism Value Desorption temperature ⁰С 85-95 Sorption temperature ⁰С 15-30 Ratio of solution flow rate to NUS volume m ³ / hour: m ³ eleven NaOH concentration g/l 20 NaCN concentration g/l 15 The ratio of the mass reg. coal : NUS t : t variable Au content at NUS initial g/t actual Au content at NUS is final g/t < 50 Au content on standard coal initial g/kg actual The content of Au on standard coal is final g/kg proportional to load Average content of Au in the solution after the end of desorption mg/l <0.10 Average content of Au in solution after sorption mg/l <0.10 Recovery of gold from NUS % depending on original content
>95% at initial grade of 1000 g/t Total time of the desorption process days 14
depending on original content

In laboratory conditions, the proposed scheme of the invention was implemented. For desorption and sorption, laboratory glass columns with a volume of 20 ml each were used, in which NUS and regenerated carbon were placed, respectively, the desorption column was heated using a jacket with a connected liquid thermostat, and water was used as a heat carrier. A control filter is installed at the outlet of the desorption column to prevent washing out of the NUS. The movement of the alkali-cyanide solution was carried out by peristaltic pumps. The conditions and results of the experiment are presented in table 2 and in figures 2,3,4. The figure 2 shows the dependence of the extraction of gold from NUS and the gold content in the desorption solution on the process time. The figure 3 shows the dependence of the extraction of gold from the NUS and the content of gold in the NUS from the time of the process. The figure 4 shows the dependence of the gold content on NUS and conditioned coal from the time of the process.

Table 2. Regime parameters and main results of desorption-sorption processes in a closed cycle

Parameter Unit ism Value Desorption temperature ⁰С 85-90 Sorption temperature ⁰С 15-30 Ratio of solution flow rate to NUS volume ml/h : ml eleven NaOH concentration g/l 20 NaCN concentration g/l 15 The ratio of the mass reg. coal : NUS g : g 12 Au content at NUS initial g/kg 0.498 Au content at NUS is final g/kg <0.050 Au content on reg. initial angle g/kg 0.160 Au content on reg. coal final g/kg 1,100 Maximum content of Au in the desorption solution mg/l 15.3 Average content of Au in the desorption solution mg/l 5.4 Average content of Au in solution after sorption mg/l <0.10 Extraction of gold from NUS (according to coal analysis) % > 90 Time to reach 90% gold recovery h 32-34 Total process time* h 56

* - by the end of the process, the gold content in the desorption drain is <0.10 g/kg

Based on the results obtained, it can be concluded that the process of gold desorption at 85-90°C and the ratio of solution rate (ml/h) and coal volume (ml) 1:1 was highly efficient, extraction from NUS with an initial content of 0.498 g/kg was >90% (residual content on NUS <0.050 g/kg). The entire saturated solution was passed through the sorption column in parallel with the desorption process, the solution after sorption was returned to the beginning of the cycle. The content on the conditioned regenerated coal in the sorption column increased from 0.160 g/kg to 1.112 g/kg. Taking into account the fact that the ratio of the mass of regenerated coal to the mass of NUS was 1:2, it was possible to concentrate gold and obtain more saturated conditioned coal from less saturated NUS. The volume loss of the circulating solution due to natural evaporation in the columns and buffer tanks was compensated by adding a fresh solution of NaCN and NaOH. Washout of NUS from the desorption column at a rate of 1:1 did not occur.

The maximum recovery rate at the highest concentration of gold in the solution after desorption at the outlet of the desorption column (15.3 mg/l) was achieved in 7 hours with the recovery of gold from NUS 22.1%. Subsequently, the desorption rate decreased, 42.7% recovery was achieved in 12 hours, 80.0% recovery was achieved in 24 hours, 90% recovery was achieved in 31-34 hours, the process was carried out 56 hours until the gold content in the solution after desorption <0, 10 mg/l until the estimated gold recovery from NUS is 95.6%.

Thus, the proposed closed scheme for the processing of NUS in columns with a clamped layer of carbon sorbent "desorption-sorption" in laboratory conditions showed high recovery rates >90%. By varying the value of the ratio of loading NUS to regenerated coal, the method is suitable for obtaining conditioned coal more saturated than the original NUS. Additional studies with a decrease in the desorption temperature below 80°C showed a decrease in the desorption rate, and at a temperature above 90–95°C, the solution begins to boil, which leads to the leaching of NUS from the desorption column.

Claims (4)

1. A method for processing substandard gold-containing coal sorbent, including a desorption operation connected to each other in the technological process, filtration of a saturated solution, sorption of a saturated solution on conditioned regenerated coal, after which the saturated coal is sent for processing to extract gold, and the depleted solution is returned to the desorption operation with the formation of a closed cycle of motion of the solution. 2. The method according to claim 1, wherein the desorption is carried out at atmospheric pressure. 3. The method according to claim 1, in which the desorption is carried out at a temperature of 85-90°C. 4. The method according to claim 1, in which the desorption is carried out with the circulation of the solution at a rate of 0.8-1.2 volume of solution per 1 volume of coal per hour.

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