Optimization practice of a gold ore beneficiation process

Foreword

Jiujiang County Dingjiashan gold mine is a small gold mine, in 1990 formally put into production. The main production processes for the pool smelt dip and heap leaching, carbon adsorption, desorption electrolysis of cyanide gold extraction process. The previous day's processing capacity was only 58t/d, the annual output was less than 30kg, and the gold recovery rate was only 70%. From June 1998 to 2003, the ore dressing process was optimized. By reducing the crushing size, controlling the optimum amount of sodium cyanide, increasing the percolation layer and using cyanide fluxing aid, improving the adsorption system, controlling the pile height, and improving the addition. Process optimization measures such as medicine and spraying system, the recovery rate of gold beneficiation increased by 15%, and the processing volume was gradually increased, eventually reaching 200t/d, which reduced the cost and significantly improved the efficiency of the enterprise.

First, the nature of the ore

Dingjiashan gold ore metal ore minerals are limonite, hematite followed by small amount pyrite, copper ore, galena occasionally, natural copper, bornite, covellite, sphalerite and arsenopyrite , native gold, silver sulfur iron ore; non-metallic minerals are quartz, siliceous water mica, kaolinite and sericite.

The gold mineral is natural gold, which is mainly embedded in limonite (86.74%) in the state of fissure gold, intergranular gold and gold, and a small amount is embedded in gangue minerals (13.26%).

The grain size of natural gold is mainly between 0.074 and 0.01 mm (accounting for 75.58%). It is a medium-fine grain gold with a shape of long-horned granules and a horny grain. It has a small amount of branches, needles and plates, and the gold forming rate is 935.8 ‰. The particle size distribution of gold is shown in Table 1.

The main useful components in the ore are gold and symbiotic iron. The associated beneficial component is silver, and the associated harmful component is arsenic , but the content is not high. The content of gold is the highest in gold-bearing limonite, followed by gold-bearing limonite, and the lowest in gold gravel. The relationship between gold and multi-element analysis is shown in Tables 2 and 3.

Table 1 Relative content of natural gold scale

Table 2 Natural gold occurrence relationship content

Table 3 Multi-element analysis of raw ore /%

Second, cyanide process parameters small test

In order to establish the optimal parameters of the Dingjiashan gold ore beneficiation process, small-scale test comparisons were made between the on-site process parameters and the improved process parameters.

(1) Tailings particle size analysis and leaching particle size test

1. Analysis of tailings particle size

From the production site tail slag yard, the tailings comprehensive sample 1000kg after cyanidation leaching was taken, and the tailings particle size analysis was carried out. The results are shown in Table 4.

Table 4 sieve size analysis of tailings

It can be seen from the tailings sieve analysis that the tailings grade is high, and most of them are distributed above the 50mm grain size. Reducing this part of the grain-level gold loss is the key to improving the recovery rate.

2, leaching particle size test

The +50mm grain size tailings sieved out from the above tailings size were divided into three parts and crushed to -30mm, -20mm and -10mm respectively, and a small cyanide leaching test of 40kg/barrel was carried out. The test conditions are as follows, and the test results are shown in Table 5.

Fixation conditions: sodium cyanide dosage 1kg/t ore, calcium oxide 5kg/t ore, pH10～ll, liquid-solid ratio 3:1, three times leaching, the first time 72h, the second 24h, the third 12h , a total of 108h.

Changing conditions: particle size -30mm, -20mm, -10mm.

Table 5 tailings leaching particle size test

It can be seen from the test results in Table 5 that the +50mm tailings can be leached by cyanidation after re-crushing, and most of the gold can be leached, wherein the -20mm particle size leaching rate is the best, reaching 66.9%, indicating that lowering the selected particle size is to improve gold leaching. The key to the rate.

(2) Sodium cyanide dosage test

In June 1998, 1000 kg of raw ore samples were taken from the raw ore yard of the plant, and the sodium cyanide dosage comparison test and different pH values ​​were tested. The test results are shown in Table 6. Test fixed conditions: leaching time 108h, liquid-solid ratio 3:1, selected ore particle size -20mm, 40kg mine / barrel; comparison conditions: sodium cyanide dosage, lime dosage.

Table 6 Sodium cyanide dosage and pH test

Before the process optimization, the amount of sodium cyanide and the amount of lime in the field were basically the same as the test of Y2 ^{# in this} test. From the above test results, it can be seen that after reducing the crushing size, the high cyano-high pH (>12) gold leaching rate is only 82.98. %, no low alkali and low cyanide process leaching rate. Under the condition of lime dosage 10kg/t (pH10～11) and sodium cyanide dosage 1.1kg/t, the leaching rate is up to 87%, indicating that the cyanide and pH process parameters must be adjusted and reduced, which can save cost and can be saved. Increase the Au leaching rate.

The results of the multi-element analysis of the test tailings are shown in Table 7.

Table 7 Multi-element analysis of tailings /%

(III) Activated carbon small adsorption test

The adsorption process passes through 3 to 4 adsorption columns equipped with activated carbon ( 50×100) After the series connection, the gold-containing solution is fed from the bottom of the first adsorption column, and the third and fourth adsorption columns are discharged at the top. Test fixed conditions: 700 mL of cyanide precious liquid; varying conditions: the number of adsorption columns connected in series. The test results are shown in Table 8. The analysis of the adsorbed noble liquid and the lean liquid after adsorption with 4 columns is shown in Table 9.

Table 8 Activated carbon adsorption test results

Table 9 Multi-element analysis of cyanide precious liquid and poor liquid g/m

It can be seen from the adsorption test that the adsorption rate of the 3-column adsorption column is only 98%, the adsorption rate of the 4-column adsorption column is 99.6%, the amount of carbon loading is increased, and the grade of gold-loaded carbon is decreased. It can be seen from this test that the adsorption rate should be increased at the site, and the number of adsorption columns should be appropriately increased.

Third, the leaching process optimization practice

(1) Optimization of pool dip process

1. Reduce the crushing size and increase the gold leaching rate

The Dingjiashan Gold Mine had two work areas before June 1998. The crushing process was only broken for a period of time, namely the PE250×400 crusher , which had a coarse crushing particle size. After the tooth plate is worn and not replaced in time, the crushing particle size is obviously coarse, the particle size is mostly below 50mm, and the coarse particle size is up to 80mm. It has been seen from the previous small test that the particle size is the main factor affecting the gold leaching rate. A piece of crushing can not meet the requirements of beneficiation, and it is imperative to make technical changes to the crushing. The author carried out a one-month crushing technical reform in the main gold production section-work area. The one-stage crushing was changed to the second-stage crushing process. It was put into production at the end of July 1998. The particle size of the original ore pool can be controlled below 15mm. After two months of trial production, the sodium cyanide dosage and lime dosage test are carried out. In October 1998, it entered formal production. In the original gold grade of 2.5, the gold grade of tailings produced in the pool dipping was reduced to 0.3-0.35g/t, and the gold leaching rate was over 86%. Compared with the crushing technology, the gold leaching rate increased by 15%, which significantly improved the mineral processing technical indicators. The annual profit for the enterprise was about 720,000 yuan.

2, reduce the amount of sodium cyanide and lime

Before June 1998, the amount of sodium cyanide in gold mine was as high as 2.0kg/t ore and 20kg/t in lime. The concentration of sodium cyanide in the precious liquid was 2‰～3‰, pH>12, sodium cyanide concentration and The pH is significantly higher. Pass the aforementioned small test. The amount of sodium cyanide and lime can be reduced by half, and the technical indicators can be improved. In August-September 1998, trial production of sodium cyanide and lime was carried out. According to production statistics, the ore grade is 2.5, the treated amount is nearly 3000t, the actual amount of sodium cyanide is 0.9kg/t ore, and the amount of lime is 9.3k. The concentration of sodium cyanide in the noble liquid can be controlled at 1.5 ‰ to 0.6 各 in each leaching. Left and right, and the concentration of sodium cyanide in lean liquid is about 0.6‰~0.8‰. Through the tracking test of the gold content of the noble liquid, the concentration of sodium cyanide and the gold grade of the tailings, the dosage of sodium cyanide and lime was reduced, and the leaching speed and the leaching rate were not affected. After the above-mentioned reduction of the crushing particle size, at the same leaching time (the leaching time is still 108 h), the tail slag gold grade is 0.3-0.35 g/t ore, and the leaching rate is 86%, which is consistent with the small test results. After reducing the amount of sodium cyanide, it can save the company about 40 tons of sodium cyanide every year and save the production cost of 360,000 yuan.

3. Improve adsorption rate and gold-bearing charcoal grade

There is only three-stage adsorption on the production site, and the gold content in the poor liquid is between 0.05 and 0.1 g/m ³ , and the adsorption rate is only 97% to 98%. It can be seen from the previous small test that the adsorption time of the 3 column is short. In October 1998, the pool dipping column was changed to 5 columns per stage, and the heap leaching was changed to 4 columns per stage. After the improvement, the gold content of the lean liquid falls below 0.0 lg/m ³ , and the adsorption rate is over 99%.

In order to improve the grade of gold-loaded charcoal. In 2000, the pool leaching was increased by the diafiltration layer, so that the amount of silt discharged from the noble liquid was significantly reduced, thereby reducing the amount of gold-bearing charcoal sand inclusions. After all the pools were immersed to increase the percolation layer, the annual production statistics were obtained. The gold-bearing grade of gold-bearing charcoal has been increased by O.7g/kg, and the grade of gold-loaded charcoal is as high as 6g/kg.

4, use the infusion agent to speed up the leaching rate and increase the leaching rate

The Dingjiashan gold deposit is a discontinuous chicken nest, which is relatively scattered and the ore grade changes very much. From January to February 1999, the ore grade of the 284 mining site contained gold as high as 40-100g/t. During the production period from 1999 to 2003, there were more than 8g/t high-grade ore. Production of high-grade raw ore conventional leaching, when the original ore contains gold grade more than 20, the leaching time needs 12d, when the original ore grade 8g / t or more takes 7d, the leaching time is significantly longer, seriously affecting the mining and production progress.

According to the gold monograph. Adding hydrogen peroxide can effectively increase the gold leaching rate and leaching speed. The author passed the on-site industrial test to increase the amount of the infusion agent - "Cyanide Fast Net" (produced by Henan Luoyang Old Town Gold Reagent Factory, 0.1kg/t ore) and hydrogen peroxide (0.3~0.5kg/t ore). The crystallization rate is obviously accelerated, the leaching time is shortened by about 30% compared with the conventional one, and the gold leaching rate is 3 to 5 percentage points higher than the conventional one.

In winter, when the temperature is 0 °C, the cyanide leaching speed is obviously slowed down, and the conventional pool leaching is extended from the usual 4.5d to 7d, and the tail slag grade can reach the standard. In the first month of January 2000, the H ₂ O ₂ immersion agent on-site industrial test was carried out. After the addition of H ₂ O ₂ (0.4-0.5 kg/t), the consumption of sodium cyanide was significantly accelerated during leaching. The gold-containing grade increased from 1.3g/m ³ to 2.2g/m, the tail slag gold grade decreased from 0.59g/t to 0.4g/t, the leaching time was shortened from 7d to 5d, and the gold leaching rate reached 84%. It is 7.6 percentage points higher than the conventional leaching rate. Through this industrial test, when the winter temperature reaches below 0 °C, H ₂ O ₂ leaching agent is added to the production to accelerate leaching and increase the leaching rate.

(II) Optimization of heap leaching process

There are 4 yards in the Dingjiashan Gold Mine. The total area of ​​the yard is 3000m ² , and the annual processing capacity of the yard is more than 10,000 tons of ore. The ore grade contains gold ore below lg/t for heap leaching. Before the technical transformation, the heap leaching rate was only 65%, and the tailings contained gold up to 0.4g/t. The main problems in heap leaching production are: coarse grain size of the heap, up to 100mm: spray can not effectively cover the yard; there are certain problems in spraying lime and dosing; carbon adsorption is only secondary; poor, noble no Separate; the entire leaching period is too long (50 to 60d). From June 1999 to 2001, reasonable improvements were made to the facilities and process problems in the yard.

1. Optimization of heap leaching process

(1) The activated carbon adsorption system was changed from the original secondary adsorption to the tertiary adsorption, from one adsorption series in the past to three adsorption series. Before the adsorption, the gold-containing precious liquid is separated from the adsorbed lean liquid. The noble liquid is adsorbed by the carbon to the lean liquid pool, and the sodium cyanide agent is pumped to the storage yard, thereby reducing the circulation loss of gold in the solution.

(2) The sprinkler system is changed from a fixed shower head to a rotary sprinkler, which is effectively distributed from the stack surface to the stack side, so that the entire yard is completely covered.

(3) Ensure the addition of lime in the yard. The ore of the Dingjiashan Gold Mine is acidic. In order to make up for the lack of pH, the site often adds lime to the precious or poor liquid pool, resulting in calcification of the surface of the gold-loaded carbon, no gold, often blocked during spraying, and low yield. To this end, the management of lime addition has been strengthened to ensure that the amount of lime in the pile is controlled at about 7 to 10 kg/t ore. The pH of the washing operation before spraying is between 1O and l1. If the pH value is insufficient, the lime is added to the heap surface and re-stacked once, and the spraying is started at the pH level.

(4) Reduce the particle size of the pile. In order to ensure the size of the ore entering the yard, a PE250×400 crusher was added to the processing of large ore, and the size of the ore was controlled to be less than 50mm.

(5) Improve heap leaching permeability. The original ore of the Dingjiashan gold deposit contains more ore and has certain clayey gangue. -0.074mm powder mine reached 33.4%, the permeability was very poor, the treatment was not good, and the channel flow phenomenon often occurred during the spraying process. The agent could not effectively penetrate into the heap and affect the leaching rate. To this end, the following measures have been taken in production:

a. The bottom of the yard is covered with a layer of 30cm thick crushed slag ore (having a particle size of about 50mm). After heap immersion for a period of time, it is often replaced at the bottom according to the bottom condition.

b. Strictly control the heap leaching height to be less than 3m.

c. In the process of entering the pile, the fine ore and crushed slag ore are mixed into the pile, and the amount of fine ore into the pile is controlled from the stope.

d. After the completion of the heap. A layer of 30 cm thick crushed slag ore is laid on the pile surface to ensure uniform penetration of the spray liquid.

After the above improvement, coupled with the use of the rotating nozzle, the problem of poor heap leaching is completely solved. The spray strength is calculated to be 10 to 16 L/(h·m ² ).

(6) Improve the dosing system. The heap leaching process is carried out in three stages, and the heap is washed first, to pH l0~l1, about ld; then enters the leaching of the drug, the first stage leaching time is 7d, continuous spraying, CN ^- 0.5 ‰; the second stage 15d, Even spray, CN ^- 0.3‰; third stage, 10d, spray one stop, CN ^- 0.1‰ ~ 0.2‰. The consumption of sodium cyanide is 0.4-0.5 kg/t ore (only half of the pool dip).

(7) Increase the amount of leaching agent to speed up the leaching. The gold content of the ore into the ore is sometimes higher than ls/t, even as high as 1.5g/t. In order to shorten the leaching time, H ₂ O ₂ (0.3-0.5 kg/t ore) was added in the first stage of heap leaching. After adding the infusion agent, the gold content in the leaching peak is as high as 2-3g/m ³ , which is 1 times higher than that of the unfilled H ₂ O ₂ heap leaching solution. The leaching time can also be completed at 30 to 35 days, shortening by 10 days. about.

2, heap leaching process optimization effect

After the above process optimization, from 2001 to the end of 2003. The technical index of heap leaching process has been greatly improved. The gold content of tailings has dropped to 0.2g/t for the whole year, and the gold leaching rate has reached 79%~81%, which is about 14% higher than that before process optimization.

Before the process optimization, the gold ore recovery rate was only 70%. Through the above process optimization practice, the ore recovery rate was increased by about 15 percentage points before the process optimization. The mineral production indicators for the past years are shown in Table 10.

Table 10 Dingjiashan gold mine over the years

Fourth, the conclusion

(1) The particle size of the infiltration is a key factor affecting the leaching rate of the Dingjiashan gold deposit. Through years of process optimization practice, the gold leaching rate is increased by 15 percentage points by reducing the crushing size and low cyanide and low alkali process. Each year, it has created more than 1 million yuan of benefits for the company.

(2) For high-grade gold ore containing more than 8g/t of ore in the original ore, use the infusion agent and “cyanide fast net”. The leaching speed is increased by 30%, and the gold leaching rate is increased by 3 to 5 percentage points.

(3) By optimizing the heap leaching process, reducing the crushing size, controlling the amount of lime, improving the adsorption system, controlling the heap height, and improving the dosing and spraying system, the heap leaching rate is increased from 65% to 79% to 81%. Effectively solve the problem of low heap leaching index of clay-bearing gold ore, and obtain better heap leaching ore dressing indicators.

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