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Pressure acid leaching of zinc concentrate B relating to the behavior of zinc sulfide sulfide pressure leaching reaction is substantially 1
ZnS+H 2 S0 4 +——0 2 —→ ZnS0 4 +H 2 0+S
2
When the absence of oxygen transfer material in the system, the above-described reaction proceeds slowly, but the dissolution of iron in the zinc concentrates, iron ion that is a good oxygen transfer material. The leaching process of ZnS is accelerated by the reduction and oxidation of iron ions.
ZnS+Fe 2 (S0 4 ) 3 —→ ZnS0 4 +2FeS0 4 +S
1
2FeS0 4 +H 2 SO 4 ——0 2 —→ Fe 2 (S0 4 ) 3 +H 2 0
2
Under normal circumstances, the concentrate contains enough acid-soluble iron to fully meet the needs of the leaching process. The oxidation of iron in pyrrhotite (Fe 7 S 8 ) or iron sphalerite (ZnFeS) is similar to the oxidation of zinc sulfide. Pyrite is inert and difficult to leach. Its oxidation is related to the leaching parameters. Pyrite will be oxidized to sulfuric acid under high temperature and strong oxidation conditions.
Copper in zinc concentrates is usually in the form of chalcopyrite, which is mostly leached.
CuFeS 2 +O 2 +2H 2 S0 4 —→ CuS0 4 +FeS0 4 +2S+2H 2 0
Galena leaching generated relatively easily lead sulfate.
1
PbS+H 2 SO 4 +——O 2 —→ PbS0 4 +S+H 2 0
2
In the case of pressure leaching, the non-pyrite sulfide in the concentrate is generally only 5% oxidized to sulfate.
MeS+20 2 —→ MeS0 4
After the formation of lead sulfate, lead species such as lead iron sputum and grass iron sputum are formed, and hydrated iron oxide is precipitated from the solution, and part of the sulfuric acid is regenerated.
It can be seen that the result of the leaching is that the zinc in the zinc concentrate is transferred to the solution, and the hydrolysis products of lead, elemental sulfur and iron remain in the slag. The behavior of sulfur in leaching is more complicated, and the main forms of its conversion products are elemental sulfur, sulfuric acid and HS0 4 - . The conversion rate of elemental sulfur is related to the operating conditions. When the acidity is high, elemental sulfur is easily formed. The acidity is lowered to make the reaction proceed to the formation of SO 4 2- and HS0 4 - . Usually, when the pH is <2, elemental sulfur is easily obtained. At 2 o'clock, it is easy to generate HS0 4 - and SO 4 2- . [next]
C Pressure Leaching Practices A major advance in direct acid leaching of zinc sulfide concentrates is the pressurized acid leaching-electrowinning process of zinc sulfide concentrates researched and developed by Sherritt Gordon Mining Company in the 1970s. The wet zinc smelting process can save the elemental sulfur from storage and transportation without the need for concentrate roasting and construction investment of SO 2 recovery facilities, eliminating SO 2 pollution and being restricted by the sulfuric acid outlet.
In 1977, the Swedish Shelter Gordon Mining Company and Cominco jointly conducted a semi-industrial test for pressurized leaching of zinc sulfide concentrate and recovery of elemental sulfur, and in the Trail smelter owned by Komenko. The first zinc sulfide concentrate pressurized acid leaching plant was established. The design capacity was 190 tons of daily processing concentrate, which was put into operation in 1981. The newly built pressurized acid leaching system runs in parallel with the original traditional wet zinc smelting process. The pressure leached pulp is combined with the original process in the acid leaching tank of the old system after separating elemental sulfur.
The Kidd Creek Mine LTD Mining Company's zinc smelter is the second zinc sulfide ore pressurized acid leaching plant designed to be produced in 1983. Germany's Ruhr Zinc Plant is the third zinc sulphide concentrate pressurized acid leaching plant with a design capacity of 300 tons per day. It was put into operation in 1991 and the iron of the plant was precipitated in the form of hematite.
The zinc concentrate pressure leaching device includes equipment required for processes such as preparation, leaching, flash discharge, waste heat recovery, and elemental sulfur recovery. The pressure leaching unit of the Teller Zinc Plant is shown below.
The materials entering the leaching autoclave mainly include: zinc concentrate ore, waste effusion and oxygen. The main components of the plant's zinc concentrate: Zn 49%, Fe 11%, Pb 5%, S 32%. Its particle size is 80% -44 μm . [next]
Firstly, the zinc concentrate is finely ground by a ball mill , and the ball mill and the hydrocyclone (lining rubber) are connected to a closed loop. The overflow of the cyclone enters the concentration tank and is concentrated by a small amount of flocculant to obtain a solid content of 68% to 70%. A slurry material having a particle size of 95% of -44 μm . The surfactant is added to the slurry in the slurry agitation tank and finally pumped into the first chamber of the autoclave.
The waste effusion is mixed with concentrated sulfuric acid, and the concentration is adjusted to 165 g/L of sulfuric acid, and the steam is exchanged with the steam produced by the slurry flash discharge tank, and the temperature of the acid is raised from about 30 ° C to 70 ° C. The purity of the oxygen for pressure leaching was 98%, which was provided by an oxygen generator.
The leaching autoclave is shown in the following figure. It has a diameter of 3.7 m, a length of 15.2 m and a volume of 103 m 3 . The casing is made of low carbon steel and is lined with lead, high temperature resistant paint and acid resistant brick. The autoclave has four chambers, each with a stirrer and baffle.
Stirring during leaching, the solid particles remain in suspension, and the oxygen and the slurry are thoroughly mixed. The zinc concentrate slurry and most of the waste effusion are pumped into the first chamber, and the acid-resistant brick overflows from the upper chamber to the next. Room, finally enter the flash tank.
Oxygen is introduced from the first three chambers, and an inert gas such as N 2 , C0 2 is continuously discharged from the first chamber with steam to prevent its accumulation. Typical operating parameters for the autoclave at the Teller Zinc Plant are as follows:
Concentrate processing capacity 190t/d
Concentrate/electrolyte 145g/L
Total pressure 1300kPa
Temperature 140～155°C
Concentrate residence time 100min
Oxygen content in the exhaust gas (dry amount) 85%
Leaching liquid H 2 SO 4 content 30g / L
The amount of Fe in the final leaching solution is 5g/L[next]
The concentrate processing capacity here refers to the design capability, and the plant has reached 250% of the design capacity in the mid-1980s. The leaching temperature is mainly provided by the heat of reaction of the concentrate. In order to maintain the heat balance in the autoclave, the waste effluent entering the first chamber is preheated, and the effluent not preheated is added to the second chamber.
The function of the flash tank is to reduce the autoclave slurry to atmospheric pressure; separate the flash steam from the hot slurry and recover the flash steam heat for preheating the waste electricity effluent into the autoclave. The flash tank and heat recovery system are shown below.
The temperature of the slurry discharged from the autoclave is about 115 ° C, and the steam is sent to the heat exchanger through the mist eliminator for heat exchange with the formulated acid. After flashing, the volume of the slurry is reduced by about 8%, and then enters the adjustment tank. The slurry is cooled to 80 ° C with a coil, and the elemental sulfur is now transformed from amorphous to monoclinic crystal.
The slurry in the adjustment tank is classified by a hydrocyclone. The overflow is mainly zinc sulphate solution and lead iron sputum and a small amount of elemental sulphur (less than lg/L), and is sent to the calcine leaching system. The underflow of the cyclone is a sulfur-rich slurry (98% of the sulfur in the leaching slurry is fed to the bottom stream), and the concentrate is selected by flotation, and the flotation tailings are combined with the main slurry system.
After being filtered and washed, the sulfur concentrate is placed in a conical melting pot together with dirty sulfur. The melt in the crucible is discharged into a pit containing dirty sulfur, and finally filtered by a filter press to obtain elemental sulfur (S99.7%). Some residue.
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