Industrial Test 1 for Separation of Arsenic from Gold-containing Flotation Concentrate by Vacuum Pyrolysis

Gold-containing arsenic sulphide concentrate arsenic is present mainly pyrite form. It has many adverse effects on the recovery of gold. When the concentrate containing high arsenic is directly cyanated, the recovery rate of gold is only 60-80% . These refining copper concentrate with a lead smelting plants and plant when charge from a pyrometallurgical process, all the products will be contaminated with arsenic melting and refractory and can generate toxic arsenic trioxide. Therefore, the effect of the fire treatment is not ideal.

In order to remove arsenic from the gold concentrate, it is necessary to oxidize the concentrate. However, since non-volatile arsenate and arsenide can be formed, arsenic can not be completely removed by oxidative roasting, and highly toxic arsenic trioxide which is difficult to collect and fusible iron and arsenic which oxidize gold particles are formed. Compound passivation. When cyanidation of iron-containing calcine is carried out, the recovery rate of gold is not high. In order to dissolve the passivation film, it must additionally be - or acid leaching some alkali leaching, and then grinding, flotation auxiliary working.    

Vacuum fumed effective method is one kind of arsenic from gold-bearing ores and concentrates in advance decomposition. The main advantage of this method is that regardless of the amount of arsenic contained in the original concentrate, a high volatilization rate and a non-toxic mixed sublimate of metal arsenic and arsenic sulfide can be obtained.

The laboratory and expanded test results show that when heated in a vacuum, the arsenopyrite will decompose, precipitate elemental arsenic and form pyrrhotite in the residue. Under this condition, the pyrite dissociates, which in turn produces elemental sulfur and pyrrhotite.

When a mixture of arsenic pyrite and pyrite is treated by vacuum pyrolysis, arsenic sulfide is formed due to the interaction of vapor arsenic and sulfur. They are easily precipitated completely in a less large condensing unit.

The gold can then be recovered from the low arsenic containing slag by methods well known. After the removal of gold, the concentrate slag containing non-ferrous metals after vacuum pyrolysis treatment is suitable for smelting in steelworks or lead smelters.

Laboratory and semi-industrial tests have been carried out on gold - arsenic concentrates of various deposits . These concentrates contain: As 2-33% ; Fe 9-36% ; S 6-33% ; SiO ₂ 5-42% ; C 0-23% ; Al ₂ O ₃ 2-15% , CaO 0.2- 3% ; MgO 0.2-3% ; Cu 0-0.6% ; Au 20 -280 grams / ton. Test proved: when the temperature is 650~ 700 °C When residual gas pressure of 0.67 to 1.33 kPa, from the thin layer and the fixed layer, a false liquefaction times may be more than 95% of the volatilized arsenic. At this time, regardless of the arsenic content in the original concentrate, the arsenic content in the slag is 0.2 to 0.5% . These slag can be recovered from gold by a known method.

According to the proportion of arsenic pyrite and pyrite in the concentrate, the sublimate contains As 64-99% and S 32-1% . This sublimate itself is a mixture of arsenic sulfide and metal arsenic. Mixed sulfides are easily melted in a neutral atmosphere. Therefore, solid solid blocks should be cast for storage and transportation.

Table 1   Test conditions and results

* The temperature of the reaction zone is high. The temperature of the slag is 40~ 50 °C .

Compact blocks for storage and shipping.

In order to volatilize volatile components from loose materials under vacuum conditions, the Institute of Mining and Metallurgy of the Kazakh Academy of Sciences and the National Institute of Rare Metals and the Central Asian Nonferrous Metals Design Institute jointly designed a continuous production. The closed heating vibrating conveyor equipment has a processing capacity of 5 tons /B and has been industrially tested.

The arsenic - carbon containing concentrate used in the test contained the following components, % : As62 ; SiO ₂ 24~Fe l6.6 ; C18.6 ; S 15.1 ; Al ₂ O ₃ 8.8 ; the pseudo specific gravity was 1.48. g / cm ³ .

The arsenic in the concentrate is mainly in the form of arsenic pyrite, while the iron is in the form of pyrite.

Granular composition of concentrate

Particle size, mm         Content %             Particle size, mm         Content %

                                                              +2.5                      19.4                          -0.2+0.16                  3.9

                                                           -2.5+1.6              4.0                        -0.16+0.1                    8.45

                                                         -1.6+0.63                     3.35                -0.1+0.063                10.4

                                                          -0.63+0.4                     2.5                        -0.063+0.05                 6.6

                                                           -0.4+0.2            2.85                             -0.05            38.6

At the time of the test, 4 tons of concentrate with a humidity of 2-2.5% were treated (see Table 1 ). When the temperature is 660~ 700 °C When the residual pressure is 6.67~9.31 kPa, the arsenic volatilization rate is 93~955% (the slag contains 0.35~0.53% arsenic ). When the temperature is 700~ 720 °C When the residual pressure is 4.0 to 5.3 kPa, the slag contained in the slag is 0.2% . During the test , the loss of As in the soot was 7.4% .

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