Ammonia leaching copper mineral raw materials and process technology

Ammonia leaching of copper ore oxidation treatment has a long history, it is only suitable for processing copper oxide ores, but also process copper sulphide ores, copper slag, tailings and other copper-containing materials. The application of hot press leaching and extraction processes opens up new avenues for the treatment of refractory copper oxides by ammonia leaching.

According to the main reaction occurring in ammonia leaching, copper mineral raw materials can be classified into atmospheric pressure ammonia immersion, hot pressure ammonia leaching and reduction roasting-ammonia leaching. If the copper mineral is a secondary copper ore and the gangue is carbonate, it can be immersed in atmospheric ammonia. Atmospheric ammonia leaching can achieve a relatively high leaching speed, leaching time is short, and the process of preparing chemical concentrates and reagents is quite simple. However, the atmospheric ammonia dip is not complete for the dissolution of copper sulfide minerals. Thus, if the addition of secondary copper minerals, but also contains copper metal and primary copper sulphide minerals too, can be hot ammonia leaching. If the copper is in the form of insoluble copper silicate or bound copper, the direct ammonia leaching effect is poor, and it should be treated by reduction roasting-ammonia leaching.

The following several examples of ammonia leaching are introduced by way of examples.

1. Hot pressing ammonia leaching method

In a large domestic copper oxide ore, the oxidation rate is 30% to 82%, and the bonding rate is as high as 10% to 47%. The main copper mineral is malachite, which accounts for more than 80%, followed by chrysocolla and other copper oxide minerals. It also contains a small amount of porphyrite, chalcopyrite and traces of natural copper. Most of the gangue are dolomite, chlorite and clay minerals, and individual ore bodies contain a large amount of carbon and mud. The ore grade is 0.6% to 0.8%, and the copper phase analysis results are shown in Table 1.

Table 1 Copper phase analysis results

At present, the copper concentrate obtained by the vulcanization-flotation method is only about 8%, the recovery rate is about 70%, and the consumption of chemicals is quite large. A large number of experiments have proved that the direct hot pressing ammonia leaching method can make the leaching rate of this low grade refractory copper ore up to 90%. The principle flow chart of the ammonia leaching intermediate test plant with a treatment capacity of 100t/d is shown in Figure 1. It consists of four steps: grinding, leaching, solid-liquid separation and distillation.

Figure 1 Principle of a semi-industrial test for hot-pressed ammonia leaching of a copper oxide ore

After the ore is crushed, it is ground to 55% (-200 mesh) with a dilute solution containing copper, carbon dioxide and ammonia. It is prepared into a slurry with a liquid-solid ratio close to 1:1, and then enters the slurry absorption tower for continuous absorption from hot-pressure leaching. The concentration of the carbon dioxide and ammonia in the gas from the trough, the auto-evaporator, the decompression tank and the distillation still reaches 8.5% to 10.2% of NH ₃ and 5.5% to 6.6% of CO ₂ after ammonia supplementation. Subsequently, the slurry is pumped to the slurry heater by high-pressure mud pump , and then enters the multi-layer berth, and is subjected to hot-pressed ammonia leaching at 120 ° C and 10.13×10 ₅ to 20.26×10 ⁵ Pa through air, and the leaching time is 2.5 h. . The main reactions of the leaching process are:

CuCO ₃ ·Cu(OH) ₂ +6NH ₃ +(NH ₄ ) ₂ CO ₃ =2Cu(NH ₃ ) ₄ CO ₃ +2H ₂ O

2Cu ₅ FeS ₄ +40NH ₃ +2CO ₂ +37/2O ₂ +nH ₂ O=8Cu(NH ₃ ) ₄ SO ₄ +2Cu(NH ₃ ) ₄ CO ₃ +Fe ₂ O ₃ ·nH ₂ O

The leaching slurry from the bottom of the berth is cooled and depressurized by the evaporator, the decompression tank, and the released ammonia, carbon dioxide and water vapor are returned to the slurry absorption tower, and the slurry for cooling and depressurization is subjected to solid-liquid separation and countercurrent washing with a concentrator. The clear liquid is sent to the distillation pot to obtain copper oxide. The distillate mother liquor is causticized to obtain calcium sulfate slag having a copper content of 10%, and ammonia combined with sulfate can be recovered. The process response is:

Cu(NH ₃ )4CO ₃ =CuO+4NH ₃ +CO ₂

(NH ₄ ) ₂ SO ₄ +Ca(OH) ₂ =CaSO ₄ +2NH ₃ +2H ₂ O

The washing water from the countercurrent washing can be returned to the grinding operation or the absorption tower. The copper leaching rate of this process is about 90%. Compared with the original flotation process, the total recovery rate can be increased by more than 10% until the copper of the electric copper is obtained.

The ammonia leaching method for copper extraction is not complicated in principle, and it has indeed achieved good indicators in unit tests in the laboratory. But to use this method as a mass production process requires a large and complex set of equipment. The semi-industrial test of 100t/d scale shows that there are two difficulties, one is that long-term stable operation cannot be achieved; the other is that the difference between actual production index and unit consumption index and corresponding theoretical indicators is very different.

Second, reduction roasting - ammonia leaching

Domestic use of reduction roasting factory - Ammonia leaching process tin oxide ore dressing plant vein reselection copper tailings, is mainly copper minerals in particulate inclusions or ionic binding state wherein copper oxide iron, copper oxide about this binding It accounts for 70% of total copper, and there are still a small amount of arsenic calcium copper ore and trace amounts of malachite and azurite. The gangue is mainly calcite , followed by quartz .

It can be known from the nature of the ore that the tailings are not suitable for acid leaching or flotation, and the flotation recovery rate is only about 30%. The isolation method requires a large amount of salt to be consumed, and the product needs further treatment. Direct ammonia leaching at normal temperature and pressure, copper leaching rate is less than 20%. The leaching rate of copper during hot pressing ammonia leaching at 160 ° C is about 75%. If reduction roasting-atmospheric ammonia leaching is used, the leaching rate of copper is about 88%, and roasting can improve the selectivity of tin, and the recovery rate of tin can be increased by 6% to 7%.

For the firing process, Sid is selected from copper mining tailings water craft to concentrate dewatering, bottom streaming kiln dried to a moisture content less than 5%, and then mixed with the ore accounts for 4% of the weight of the brown coal dust at 750 ~ 850 ℃ The reduction roasting is carried out in the rotary kiln, so that most of the ore is combined with copper to be converted into free copper oxide, and a small part is reduced to metallic copper:

3(CuO·Fe ₂ O ₃ )+C=3CuO+2Fe ₃ O ₄ +CO

3(CuO·Fe ₂ O ₃ )+4CO=3Cu+2Fe ₃ O ₄ +4CO ₂

The reduction roasting kiln operates in a downstream flow. There is a cooling section of several meters in the tail of the kiln. The calcine is sent to the quenching tank and the returned copper-depleted ammonia solution by screw conveyor to adjust the liquid-solid ratio (2~3): 1 slurry, pumped to mechanically agitated gas turbine for leaching. The tank is leached.

The leaching is carried out in three stages, and each section is subjected to solid-liquid separation after leaching, and finally a four-stage countercurrent washing is carried out, and both the solidification separation and the backwashing are carried out in a concentrator. The leaching temperature was 45 to 50 ° C, and the leaching agent contained ammonia 65 g/L, carbon dioxide 40 g/L, and leaching time 3.5 h. The washed bottom stream is sent to beneficiation to recover tin and iron. The copper-rich ammonia solution after leaching is sent to the ammonia-sink copper to obtain copper oxide having a copper content of about 65%. Ammonia steam generated ammonia, carbon dioxide gas is condensed and returned absorbent leaching operations.

Third, ammonia leaching - sulfide precipitation - flotation method

Ammonia leaching - sulphide precipitation - flotation method is the addition of elemental sulphur (sulfur powder) during the pressure leaching process. Immediately after the copper oxide mineral is dissolved by NH ₃ -CO ₂ , it is precipitated into copper sulphide. Pulp without solid-liquid separation is directly distilled in the recovery after _2, the precipitated "artificial copper sulfide", and any original natural ore together with a sulfur copper recovery of NH ₃ and CO conventional flotation, the flotation of fine products mine. The principle process is shown in Figure 2.

Figure 2 Flow chart of ammonia leaching - sulfide precipitation - flotation principle

Compared with the full ammonia leaching process, this method has the following advantages:

(1) The copper sulfide mineral in the ore does not need to be oxidized and leached, and can still maintain its natural state and then float together with the artificial copper sulfide. This simplifies the original oxidation process in the leaching process.

(2) Eliminating the huge solid-liquid separation process. This not only greatly simplifies the process, reduces equipment, and avoids the loss of copper and various reagents during solid-liquid separation.

(3) From the past solution of steamed ammonia to the direct slurry of ammonia in the slurry, the heat consumption is reduced, and the problem of crusting in the distillation tower is greatly alleviated.

The downside is that the final product is copper concentrate. The small and industrial tests of the Tangdan Copper Oxide Mine of the Dongchuan Mining Bureau show that the basic conditions for the ammonia leaching-sulfurization-flotation process are: ore particle size of 55% (-200 mesh), liquid-solid ratio of 1:1, The leaching temperature is 140 °C, the NH ₃ and CO ₂ concentrations are 5N and 2.5N, respectively, and the leaching time is 2~3h. The comparison of the semi-industrial test results with the theoretical amount of sulfur is shown in Table 2. It can be seen from the table that the ammonia leaching-sulfurization-flotation process did take a breakthrough in the past, the copper recovery rate increased by 17%, and the concentrate grade was one and a half times.

Table 2 Comparison of ammonia leaching-sulfurization precipitation of Tangdan refractory copper oxide ore and conventional vulcanization flotation

IV. Segregation-flotation method

Segregation-flotation is a process in which the ore (slag) which is difficult to be treated by conventional single flotation is first heat-treated, and its chemical composition and physical structure are completely changed in favor of flotation, and then the method of flotation of sulfide ore is used. Separate its valuable metals and their minerals from the gangue.