Study on improving recovery rate of an arsenic-containing gold ore

Smelter using a gold-containing arsenic CIP Process sulphides carbonaceous gold ore. Due to the complex composition of ore and high arsenic content, the cyanidation leaching rate of gold has been hovering around 75% to 77% for many years, and the resource utilization rate is low. In order to further improve the economic benefits, the tower grinding machine fine grinding and alkaline normal temperature and pressure pretreatment process ^{[1 ~ 3]} were used to carry out research on improving the recovery rate of gold ore, and provide technical solutions for production transformation.

First, the nature of the ore

The ore is a type of polymetallic high arsenic sulfide with complex composition. In the ore: Au 16.4 g / t, Ag 16 g / t, As 2.0%, S 10.7%, C 0.3%, Fe 6.5%, Pb 0.15%, Zn 2.8%, Cu 0.1%. Metallic minerals are mainly pyrite, followed by sphalerite, galena, pyrrhotite, arsenopyrite ore and some brass, copper, blue and occasionally tetrahedrite. Non-metallic minerals are quartz, sericite and a small amount of calcite. No graphite minerals were found by carbon content test and microscopic analysis of rock and mineral light. Carbon is mainly derived from carbonate. Although there is a small amount of organic carbon, the adsorption capacity is not strong.

Gold is mainly in the form of independent gold minerals; it is divided into granular and irregular; mainly distributed in fissure gold, inclusion gold, and interstitial gold in the fissures of pyrite; secondly, inclusion gold, crystal gap gold wrapped in yellow Iron ore and the crystal gap distributed in pyrite and quartz, and some of the gold in the poisonous sand are present; the gold particles are mainly fine particles and fine particles, and most of them are distributed between 0.035 and 0.0025 mm.

Second, the test

(1) Process and equipment

The process flow used in the test is shown in Figure 1. The instruments and equipment used for the test mainly include: tower type immersion machine, enhanced alkali immersion stirring tank, thermometer, pH meter, air compressor, flow meter, cyanide and carbon adsorption tank.

Figure 1 Test process

(two) test reagents

The reagents used are mainly: NaOH (IR), NaCN (AR), CaO (IR), Ca (ClO) 2 (IR), Fe 2 (SO ₄ ) ₃ (AR). The test water is municipal tap water.

(3) Test conditions

The basic test conditions are shown in Tables 1-3.

Table 1 Grinding conditions

Table 2 Enhanced alkali leaching conditions

Table 3 Cyanidation and carbon adsorption conditions

Third, the test results and discussion

(1) Fine grinding direct cyanidation

Direct cyanide leaching of ore was carried out under the conditions of -200 mesh mass fraction of 85%, 95%, and -400 mesh mass fraction of 95%. The test results are shown in Table 4. As the fineness of grinding increases, the gold leaching rate tends to increase. Under the above three kinds of grinding fineness cyanidation for 24h, the leaching rates of gold were 75.6%, 77.4% and 86.6%, respectively. The gold leaching rate of -200 mesh mass fraction less than 95% grinding fineness is only slightly higher than the gold leaching rate of -200 mesh mass fraction less than 85% grinding fineness; but when the grinding fineness reaches -400 mesh mass fraction At 95%, the gold leaching rate increased significantly, which was 11% higher than the grinding fineness -200 mass fraction of 85%.

Table 4 Grinding fineness test

(2) Strengthening alkaline leaching pretreatment

Although the oxidation of arsenopyrite has a great thermodynamic trend, its natural oxidation reaction in water and air has a half-reaction period of 24000d, and the natural oxidation kinetics is very slow. Under the same conditions, the oxidative decomposition rate of arsenopyrite is about 4.5 times higher than that of pyrite. However, after the fine grinding and activation of the tower type grinding machine, the thermal stability of the mineral is reduced, the acid and alkali resistance is weakened, the solubility, activity, reaction speed and the like are improved, and the oxidation reaction of the arsenic sulfur mineral can be performed under high temperature and high pressure. Occurs under normal temperature and pressure. Therefore, tower grinders can strengthen and accelerate certain chemical processes. It is both a high-efficiency fine grinder and an activator, and can also be a pre-leader, pre-oxidizer ^{[1 ~ 3]} or pre-flotter ^[4] .

At room temperature of -200 mesh mass fraction of 95% and -400 mesh mass fraction of 95%, the atmospheric temperature and atmospheric pressure enhanced alkali leaching pretreatment was studied. The arsenic sulfide mineral is oxidized by alkali leaching and further converted into arsenate (iron, calcium) precipitate, calcium sulfate, iron hydroxide and ferric oxide, etc., which do not affect the cyanide leaching, so as to be encapsulated in the arsenic sulfur mineral. Gold chemical dissociation to obtain a satisfactory gold recovery rate. The results of the pretreatment test are shown in Table 5.

Table 5 Enhanced alkali leaching pretreatment results

As the agitation enhanced alkali leaching progresses, arsenic and sulfur minerals are selectively oxidized and arsenic minerals are preferentially oxidized, and a grinding fineness ratio of -400 mesh mass fraction of 95% is -95 mesh mass fraction of 95%. The degree of pretreatment is good. The alkali leaching was strengthened for 8,16,24h. Under the grinding fineness of -400 mesh with a mass fraction of 95%, the oxidation rate of arsenic was 73.0%, 86.5%, 89.0%, and the sulfur oxidation rate was 13.2%, 19.8%. 24.5%, the corresponding 24 h cyanide leaching rate of pre-oxidation time gold was 90.9%, 93.3%, 94.2%. Under the grinding fineness of -200 mesh mass fraction of 95%, the arsenic oxidation rates corresponding to different pre-oxidation times were 65.5%, 77.0%, 85.5%, respectively; the sulfur oxidation rate was 11.3%, 17.6%, 21.8%. The 24h cyanidation leaching rates of the corresponding gold were 90.2%, 91.5% and 92.1%, respectively. The fine grinding and enhanced alkali leaching pretreatment process meets the mineralogical dissociation requirements of arsenic-containing gold ore and achieves high gold recovery. Through the comprehensive comparison of technology and economy, the gold recovery result of pre-oxidation for 16h under the grinding fineness of -400 mesh mass fraction of 95% is the best.

Figure 2 shows the kinetics of NaOH and CaO consumption and the change of slurry temperature during the enhanced alkali leaching pretreatment. The results in Figure 2 show that the temperature of the slurry rises rapidly due to the exotherm of the alkali leaching reaction. After strengthening alkali leaching for 1.5h, the pulp temperature rose from the initial 8.5 °C to the peak point of 51 °C, and the alkali consumption rate of ton was also the highest at the same time, about 15kg/h. Pre-oxidation for 1.5 to 4 hours, the temperature of the slurry is maintained at 50 ° C, and the average alkali consumption rate of the ore mine is 5.6 kg / h. Alkali leaching for 4.5-8 h, the temperature of the slurry decreased slightly and remained at the level of 48 °C. After pre-oxidation for 8 h, CaO was used and added from 10.5 h. The slurry temperature also slowly decreased and remained at 46.5 °C. Preoxidation of 10.5 ~ 13.5h and 13.5 ~ 15h, the rate of consumption of CaO per ton of mine is 2.2kg / h and 6.7kg / h. Pre-oxidation for 15 to 16 hours without addition of CaO. Pre-oxidation for 16 h, the total consumption of NaOH was 45 kg / t, CaO was 20 kg / t.

Figure 2 NaOH, CaO consumption kinetics and changes in slurry temperature

(5) Economic evaluation

Using a tower grinder with a fine grinding capacity of 50 t/d, the ore fineness of the ore is increased from 85% of the existing production of -200 mesh to 95% of -400 mesh, and the grinding classification cost is 15 yuan/t. Alkaline leaching pre-oxidation for 16h, stirring and venting power consumption of 27 yuan / t, NaOH and CaO consumption cost of 84 yuan / t, fine grinding and alkali leaching pre-treatment increased the cost of 126 yuan / t. Since the gold extraction cost of subsequent operations such as cyanidation is the same as the environmental emission control cost and the direct cyanidation method, the increased production cost is unchanged after the fine grinding classification and the enhanced alkali leaching pre-oxidation system. The equipment to be added includes a tower type immersion machine, a cyclone, a pre-oxidation agitation tank and a fan, with an investment of about 900,000 yuan.

The recovery rate of gold increased from 75.6% to 93.3%, and 2.9g of gold could be recovered per ton of ore. The price of gold was 105 yuan/g, and the output value of ton ore was 304.5 yuan. Deducted from the increased production costs, the tonnage increased by 178.5 yuan. According to the production capacity of 50t/d, 145g of gold is recovered every day, and the output value is increased by 15,525 yuan, and the profit is 8,925 yuan. The annual production time is calculated according to 300d. The annual recovery of gold is 43.5kg, the output value is 4.66 million yuan, the profit is 2.68 million yuan, and the investment is recovered in 3 and a half months.

Fourth, the conclusion

The gold ore with a mass fraction of 2% arsenic was pre-oxidized for 16 h under the grinding fineness of -400 mesh mass fraction of 95% by fine grinding with a tower grinder and alkaline normal temperature and atmospheric pressure strengthening pretreatment. The recovery rate of gold cyanide increased from 75.6% before fine-ground alkali leaching to 93.3%. The operating cost of the fine grinding and alkaline leaching pretreatment system is about 126 yuan / t. This technology is used to carry out technical transformation of the 50t/d gold smelter, which can recover 43.5kg of gold per year. The equipment investment of the fine grinding and pretreatment system can be recovered in three and a half months.

references

[1] Meng Yuqun. Study on the principle of normal-temperature and atmospheric-pressure enhanced alkaline leaching pretreatment in refractory gold ore and its key technologies in industrial application [D] . Beijing: Graduate School of Chinese Academy of Sciences, 2003.

[2] Meng Yuqun. Alkaline normal temperature and pressure pre-oxidation of refractory arsenic gold concentrate [J] . Precious Metals, 2004, 25 (3): 1~5.

[3] Meng Yuqun, Wu Minjie, Su Shaoling, et al. Study on the industrialization of alkaline normal temperature and atmospheric pressure strengthening pre-oxidation of arsenic-containing refractory gold concentrates [J] . Gold, 2004, 25 (2): 26~31.

[4] Meng Yuqun, Wu Minjie, Su Shaoling, et al. Experimental study on the new process of edge grinding[J] . Mining and Metallurgy Engineering, 2003, 23 (1): 28~30.

Author unit

Institute of Metal Research, Chinese Academy of Sciences (Meng Yuqun, Su Shaoling)

Shenyang Nonferrous Metal Research Institute (Dai Shujuan)

Other Fittings for instrumentation, refrigeration, hydraulic, pneumatic, automotive and industrial applications.