Experimental study on cyanidation leaching of low-grade refractory gold ore containing arsenic and antimony

I. Introduction

With the development of gold mining industry, easy to deal with in today's gold resources dwindling, in-depth study of refractory gold ore dressing and smelting technology, development and utilization of such resources has great practical significance.

The author of the carbon-containing arsenic, antimony somewhere northwest of refractory low-grade gold ore treatment process and the nature of a number of studies, preliminary control characteristics of the ore, and to explore the optimum conditions to process the ore by heap leaching.

Second, the nature of the ore

(1) Mineral composition of ore

The limonite ore mineralization genus, of sericite, quartz sandstone type reticulata of gold ore. Surface ore is highly oxidized, weathered and broken, and muddy is more serious. The main minerals in the ore are quartz, limonite, pyrite, arsenopyrite, stibnite and carbonaceous materials.

(2) The chemical composition of the ore

The main chemical composition of the ore is shown in Table 1.

Table 1 Analysis of main elements of ore

ingredient

Au*

Ag*

Cu

Pb

Zn

As

Sb

S

C

CO 2

Hg*

/10 -2

2.02

50.0

0.003

0.008

0.06

0.35

0.48

0.17

0.43

1.56

0.40

* /10 -6

It can be seen from the results in Table 1 that the content of the impurity elements As, Sb, and C which affect the gold cyanide leaching in the ore is high.

(3) Granularity characteristics of ore

The ore sample having a particle size of -40 mm and a grade of 2.05 g/t was sieved, wherein the yield of the -200 mesh fraction was 10.76%, the gold grade was 6.57 g/t, and the gold distribution was 34.42%. The yield of -0.9mm grade is 37.20%, the gold grade is 3.52g/t, and the gold distribution rate is 63.78%. This shows that after the ore is broken, gold is enriched in the fine fraction. The ore content in the ore is high, which affects the permeability of the heap during heap leaching.

(4) Leaching characteristics of gold in ore

The original ore sample of -200 mesh was calcined with aqua regia and the gold grade was measured to be 2.02 g/t. The original ore sample of -200 mesh was directly immersed in aqua regia for 1 h without calcination. The leaching rate of gold was 58.42%, and the gold grade of tailings was 0.84 g/t. When the -200 target ore sample was directly immersed in reverse aqua regia for 1 h without calcination, the gold leaching rate was 78.71%, and the tail slag gold grade was 0.43 g/t.

The above leaching results indicate that the ore is of a difficult dip type. When the -200 mesh unbaked material is leached with hot aqua regia, the gold leaching rate is only 58.42%, and 41.58% of the gold is either encapsulated in the arsenopyrite and stibnite or adsorbed by the carbon in the ore, leaving at the end In the slag. When the anti-king water leaching, the gold leaching rate was only 78.71%, indicating that 20.29% of the gold-coated sulphide was leached, and 21.29% of the gold was still not leached due to carbon and other factors in the ore. From this point of view, the conventional cyanide leaching rate of the ore is difficult to exceed 58%.

(5) Effects of arsenopyrite, stibnite and carbon on gold leaching

The arsenopyrite can be oxidized to form Fe 2 (SO 4 ) 3 , As(OH) 3 , As 2 O 3 , etc., and As 2 O 3 can react with cyanide to form HCN to consume cyanide.

As 2 O 3 +6NaCN+3H 2 0==2Na 3 AsO 3 +6HCN↑

In addition, the sulfides of arsenic and antimony are well soluble in alkali to form arsenite, thioarsenite, tellurite and thioarsinate, such as:

Sb 2 S3+6NaOH==Na 3 SbS 3 +Na 3 SbO 3 +3H 2 0

2Na 3 SbS 3 +3NaCN+3H 2 0+1.5O 2 ==Sb 2 S 3 +3NaCNS+6NaOH

These reaction products all form a film on the surface of the gold mineral, which seriously hinders the interaction between gold and O 2 and CN - ions, making the gold cyanide reaction difficult.

Third, the whole mud cyanide leaching test of ore

For the original ore sample with the grade of 2.02g/t and the fineness of -200 mesh with a mass fraction of 95%, after the different pretreatment, the whole mud cyanide leaching test was carried out. The conditions and results of the test are shown in Table 2.

Table 2 Test conditions and results of all mud cyanidation test

Test content

Test conditions

gold

Leaching

rate/%

Remarks

Pulp

concentration

/%

pH value

(NaC

N)/%

Leaching time / h

Direct cyanidation

Roasting cyanide

Cyanide carbon immersion

Addition of lead nitrate cyanide

Cyanide after pretreatment with sodium hydroxide

Cyanidation after diesel pretreatment

Add cyanogen bromide (BrCN) soaked in hydrogen peroxide pretreated co

28.6

40.0

40.0

40.0

40.0

28.6

28.6

28.6

11

11

11

10.5

13

11

10.5

11

0.08

0.13

0.13

0.13

0.13

0.08

0.08

0.08

20

21.5

12

18

12

twenty one

20

20

45.54

70.30

60.38

55.94

54.46

50.50

50.00

47.52

600 ° C, roasting for 1 h

The density of charcoal is 35g/L

Add 0.5kg/t lead nitrate and cyanide after stirring for 3h

Cyanidation after 2h NaOH pretreatment for 12h

240g/t diesel, 50% pulp concentration, cyanidation after 2h stirring

The amount of cyanogen bromide is 0.5kg/t

H 2 O 2 was added in an amount of 2 ml/L, pre-oxidized for 13 h.

The results in Table 2 show that after the cyanidation and carbon leaching of the ore sample, the leaching rate of gold is greatly improved, which is increased by 24.76% and 14.84% respectively; the ore sample is added with lead nitrate or cyanogen bromide or After cyanidation with sodium hydroxide, the leaching index of gold was improved; but in general, the index of stirring cyanide leaching was not high.

Fourth, ore column leaching test

For the original ore sample with a particle size of -40 mm and a grade of 2.02 g/t, a column immersion test with cement granulation and lime addition was carried out. The test conditions and results are shown in Table 3.

Table 3 Column immersion test conditions and results

Test number

Test conditions

test results

Cement consumption / (kg · t -1 )

Lime consumption / (kg·t -1 )

Sodium cyanide consumption / (g·t -1 )

Leaching time / d

Penetration velocity / (L·m -2 h -1 )

Original gold grade / (g·t -1 )

Tail gold grade / (g·t -1 )

Gold leaching rate /%

1

2

3

4

5

5

8

5

3

5

84.7

42.5

50.7

66.8

80.8

16

18

twenty two

17

18/

5084

15729

497

385

678

2.09

2.02

2.12

2.06

1.47

0.81

0.82

0.85

0.86

0.60

61.24

59.41

59.91

58.25

59.18

Note: After the test, the column ore sample is washed with an aqueous solution of 0.01% NaOH and H 2 0 2 in an amount of 2 ml/L.

Whether it is cement granulation or lime as a protective base for column leaching, the leaching rate of gold is between 58% and 61%, which is higher than the result of stirring cyanide leaching.

V. Discussion of test results

After cyanidation and carbon leaching after ore roasting, the leaching rate of gold is greatly increased because the carbon robbing in the ore is eliminated or weakened. The sodium hydroxide solution pretreats the ore to dissolve the surface of the arsenic and antimony sulfides, and some of the encapsulated gold is exposed, thereby increasing the gold leaching rate. The addition of lead salt to the cyanide solution not only eliminates the adverse effects of S 2- on the gold leaching in the slurry, but also accelerates the oxidation of films such as thioarsenite and thioarsenite formed on the gold surface. The surface of the passivated gold particles is restored to activity. The addition of diesel fuel forms a protective film on the surface of the carbon to alleviate its "golden" effect.

The test results show that the column leaching index is significantly higher than the conventional total mud cyanidation. The main reason is that during the column leaching process, the contact time between the gold-containing solution and the carbon in the ore is short, and the phenomenon of carbon “robbery” is not so serious. In addition, hydrogen peroxide was added to the column immersion and subjected to alkaline washing. Hydrogen peroxide also oxidizes the thioarsenite and thionitrite films formed on the gold surface.

For low-grade gold ore with a small amount of carbon, a low-cost heap leaching process is suitable. In order to increase the leaching rate of gold, the contact time of the noble liquid with carbon in the ore should be reduced as much as possible. In the heap leaching production, the following measures can be taken: the ore is granulated to improve its permeability; during the pile-up process, the pile-up machinery is prevented from compacting the pile; and the bottom pad of the yard is laid 0.2-0.3 m thick. The coarse ore is made into a permeable layer, and a collecting pipe is laid under the heap to reduce the residence time of the precious liquid in the heap; reducing the gold grade of the cyanide solution of the spray heap, and also reducing the carbon in the ore. The role of robbery. The “secondary adsorption” process for leaching precious liquid can not only improve the grade of gold-loaded carbon, but also provide low-grade gold cyanide solution for spraying operation.

For ore with high content of arsenic and antimony, during the leaching period, appropriately increasing the alkali washing operation and adding an appropriate amount of hydrogen peroxide also have a certain effect on increasing the leaching rate of gold.

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