Henan gold ore to occur in porphyry, granite rocks sheet addiction sulfide ores, because of disseminated gold fine particle size, and the portion of the carrier of iron ore Golden affected local alteration and weathering is oxidized to Limonite is therefore difficult to handle gold ore. In this study, the ore was subjected to flotation test and full mud cyanide leaching test, and the way to rationally develop and utilize the ore was sought.

First, the nature of the ore

The metal minerals of a gold ore in Henan mainly include pyrite, magnetite, limonite, hematite, etc. The gangue minerals are mainly feldspar , quartz , chlorite and calcite . The results of multi-element analysis of ore chemistry are shown in Table 1.

Table 1 Multi-element analysis results of ore chemistry

Note: The content of Au and Ag is g/t.

There are three main forms of gold in the ore: one is visible gold in the form of natural gold and silver gold ore. This part of the gold is generally finer and is filled along the ore hole or distributed along with other detrital minerals. In the silicate; the second is in the form of carrier in pyrite, limonite; the third is in the gangue, this part of the gold content is less, mainly in the form of fine-grained gangue wrapped gold and continuum . The calculation results of gold distribution and balance are shown in Table 2.

Table 2 Gold distribution and balance calculation results

It can be seen that the ore has the characteristics of low gold grade, high pyrite content, partial oxidation of gold sulfide to limonite, and fine grain size of gold embedding (<10 μm).

Second, flotation test

(1) Test of rough selection conditions

The rough selection condition test was carried out according to the flow of Fig. 1.

Figure 1 rough selection test procedure

1. Flotation grinding fineness test

The effective monomer dissociation of natural gold and gold-bearing minerals is the basic condition for ensuring concentrate quality and gold recovery. According to the relevant literature and experience, according to the flow of Figure 1, under the condition that the adjusting agent is sodium carbonate 1 000 g/t and the collector is 100 g/t + butyl ammonium black drug 30 g/t, the different grinding fines are investigated. The effect of degree on flotation index, the test results are shown in Table 3.

Table 3 Flotation grinding fineness test results %

Note: The Au grade unit is g/t.

It can be seen from Table 3 that as the grinding fineness becomes finer, the yield of coarse concentrate increases significantly, and the grade of tailings decreases. The recovery rate of coarse concentrate begins to increase more, but when the grinding fineness exceeds -200 mesh 80% After that, the increase is not obvious. This is because the grinding fineness is too fine, the ore is muddy and affects the flotation effect. Therefore, it is determined that the grinding fineness is - 0.074 mm, which accounts for 80%.

2. Adjusting agent type and dosage test

The natural pH of the pulp is about 6, which is weakly acidic. Since most of the gold in the ore is distributed in pyrite and in the form of natural gold, it should be collected in neutral or alkaline media. Sodium carbonate can not only adjust the pH value of the slurry, but also have a certain activation effect on the sulfide minerals, and can disperse the slime and improve the mineralization effect. Therefore, according to the flow of Fig. 1, under the condition that the grinding fineness is -0.074 mm, 80%, and the collector is 100 g/t + butyl ammonium black drug 30 g/t, sodium carbonate is used as a regulator. The impact on the flotation indicator. The test results are shown in Table 4.

Table 4 Test results of sodium carbonate dosage

It can be seen from Table 4 that the flotation index is improved by adding an appropriate amount of sodium carbonate. With the increase of the amount of sodium carbonate, the recovery rate of coarse concentrate increased, and the grade of tailings decreased. However, when the amount of sodium carbonate exceeded 1000g/t, the recovery rate of coarse concentrate was limited. Therefore, the amount of crude sodium carbonate selected was 1000 g/t.

The test results show that the use of sodium carbonate can effectively disperse the slime and have a certain activation effect on the sulfide minerals, thus obtaining a better flotation index. However, considering that sodium carbonate is much more expensive than lime, the flotation effect using lime as a modifier is compared. The test results are shown in Table 5.

Table 5 Comparison test results of lime and sodium carbonate

Table 5 shows that when lime is used to adjust the pH value, the flotation foam layer becomes thinner, the amount of foam is greatly reduced, and the crude concentrate yield and recovery rate are significantly reduced. Therefore, it was determined to use sodium carbonate as a regulator.

3, collector type and dosage test

According to the flow of Fig. 1, under the condition that the grinding fineness is -0.774 mm, 80%, and the adjusting agent is sodium carbonate 1 000 g/t, the influence of the type and amount of the collector on the flotation index is investigated. See Table 6.

Table 6 Test results of collector types and dosages

It can be seen from the test results that the combination of Dinghuang and butyl ammonium has a good harvesting effect. With the increase of the dosage of the combination of butyl sulphate and butyl ammonium black drug, the recovery rate of rough selection is improved, but after the dosage of butyl xanthate + butyl ammonium black reaches 100 + 30 g / t, the recovery rate of coarse concentrate is no longer Significantly improved. Therefore, it was determined that the combination of Dinghuang and D-ammonium black drug was used as a collector, and the crude selection amount was 100 + 30 g/t.

(2) Sweeping sodium sulfide dosage test

In view of the fact that some pyrite in the ore is oxidized into colloidal pyrite and limonite, and in order to avoid the suppression of the easy-floating pyrite and not affect the concentrate grade during the selection, it is considered to add an appropriate amount of sodium sulfide during the sweeping. To improve the gold recovery rate. According to the flow of Figure 2, the sodium sulfide dosage test was carried out. The test results are shown in Table 7.

Figure 2 sweeping sodium sulfide dosage test process

Table 7 Results of sweeping sodium sulfide dosage test

It can be seen from the test results that the recovery rate of the middle mine is increased when 200 g/t sodium sulfide is added by sweeping; the amount of sodium sulfide is continuously increased, and the sweeping index is worse. Therefore, the amount of sodium sulfide added was selected to be 200 g/t.

(3) Closed circuit test

On the basis of the previous conditional test, a closed circuit test was carried out according to the flow of Fig. 3, and the test results are shown in Table 8.

Figure 3 closed circuit test process

Table 8 Closed circuit test results

The results in Table 8 show that under the optimal process conditions, the gold grade of the concentrate obtained by flotation is only 18.72 g/t, and the index is not ideal. This is due to the high pyrite content and low gold enrichment. Therefore, it is necessary to further study the effect of the whole mud cyanide leaching process on the recovery of gold.

Third, the original mud cyanide leaching test

The effects of main processing conditions such as fineness of grinding, sodium cyanide and cyanide leaching time on gold leaching rate were investigated.

(1) Cyanide leaching grinding fineness test

In the ratio of slurry to solids ratio of 2:1, the pH of the slurry was controlled to about 11.5 with the protection of soda lime, the amount of NaCN was 5 kg/t, and the agitation of the gold was leached for 24 h. The effect is shown in Table 9.

Table 9 Cyanide Leaching Grinding Fineness Test Results

From the test results, as the fineness of the grinding becomes fine, the gold leaching rate continues to increase. Although the grinding fineness is -0.045 mm, accounting for 97 010, the gold leaching rate can reach 88.89%, but compared with -0.074 mm, which accounts for 90% of the grinding fineness, the grinding cost will be greatly increased. Therefore, considering the comprehensive consideration, it is determined that the grinding fineness is -0.074 mm and accounts for 90%.

(2) Protection of alkali lime dosage test

In the process of cyanidation, the addition of a certain amount of alkali can prevent the hydrolysis of cyanide and increase the utilization of cyanide. However, if the alkalinity is too high, the dissolution rate of gold will be reduced. Therefore, the effect of the amount of protective soda lime on the gold leaching rate is investigated. . The test conditions were grinding fineness -0.074mm, 90%, slurry ratio: 2:1, sodium cyanide 5 kg/t, leaching time 24 h, test results are shown in Table 10.

Table 10 Test results of protecting alkali lime

The test results show that the gold leaching rate is higher when the amount of soda lime is 4 kg/t, and the leaching rate is affected by too high and too low lime. Therefore, the amount of protective soda lime is 4 kg/t, and the corresponding pulp pH is 11.5.

(III) Sodium cyanide dosage and leaching time test

In the grinding fineness of -0.074 mm accounted for 90%, the slurry solids were 2:1, and the lime slurry was adjusted for 5h to stabilize the pulp pH at 11.5 right. The initial concentration of sodium cyanide and the leaching time were observed for gold leaching. The impact of the rate. The test results are shown in Table 11.

Table 11 Test results of sodium cyanide dosage and leaching time

From the test results, when the addition of 1kg / t sodium cyanide, cyanide leaching for 72 h, the leaching rate of gold is the same as the leaching rate of adding 2 kg / t sodium cyanide, cyanide leaching for 24 h, are 81. 11%, while the former consumption of sodium cyanide is only 0.64 kg / t, the latter consumption of sodium cyanide reached 1.08 kg / t. Therefore, by using a lower cyanide concentration and prolonging the cyanide leaching time, sodium cyanide consumption can be reduced without affecting the leaching rate.

Fourth, the conclusion

(1) Some pyrite in a gold ore in Henan is oxidized into limonite. Gold is mainly present in pyrite, limonite and gangue in microscopic and ultramicroscopic state, and occasionally there is about 10μm. Micro-visible gold is a difficult gold ore.

(2) On the basis of the research of process mineralogy, a detailed flotation test was carried out on the ore, and a coarse and two fine two-sweeping process was adopted. The obtained process index was concentrate gold grade 18.72 g/t, gold recovery. The rate is 72. 55%.

(3) The results of the whole mud cyanide leaching test show that the use of lower cyanide concentration and prolonged cyanide leaching time can reduce the consumption of sodium cyanide. The grinding fineness is -0.074mm, 90%, the slurry solid ratio is 2:1, and the lime slurry is adjusted for 5h to stabilize the pulp pH at about 11.5, and 1 kg/t sodium cyanide is added to cyanide leaching. At 72h, the gold leaching rate was 81.11%.

(4) It can be seen from the comparison that the flotation process is adopted for a gold ore in Henan, and the technical index of the gold concentrate obtained is lower, and the full leaching effect can be obtained by using the whole mud cyanide leaching process. Therefore, it is recommended to use the whole mud cyanide. The ore is processed by a leaching process.

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