Arsenic removal process of several typical copper enterprises
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A, arsenic recovery El Indio copper mine
From 1981 to 2003, the El Indio copper mine in Chile had been using roasting to recover arsenic trioxide (As 2 O 3 ), making copper concentrate more suitable as a smelting material for copper smelters. The arsenic removal process of the mine is shown in Figure 1.
Figure 1 Arsenic treatment process in the El Indio mine
Each of the three calciners consisted of 14 Nicols Herreshoff units with a furnace diameter of 6.5 m. Each roaster is fed through a double-seal ram device at the top of the weighing belt and the roaster, at a feed rate of 6.5 to 7 t/h. In the upper six furnaces, air is injected to form a weak oxidizing atmosphere, thereby generating an exothermic reaction between arsenic and sulfur. The temperature distribution in the calciner is maintained between 630 ° C and 720 ° C. In the lower furnaces (7 to 14), the atmosphere is maintained in a strongly reduced state, producing assorted As 2 S 3 and Sb 2 S 3 and elemental sulfur. The calcine is discharged through the grille, cooled in a water jacket screw conveyor, wetted and stored in a sealed warehouse, transported by truck to a local copper smelter or through a port to other copper smelters.
The roasting extraction rates of arsenic and antimony are about 95% and 45%, and about 42% of the sulfur content is left in the calcine. Specific data, see Table 1.
Table 1 Extraction rate of As, Sb and S in EI Indio roaster (%)
element
materials
Roasting
Extraction rate
As
7.2
0.48
94.5
Sb
0.54
0.36
44.5
S
34.4
24.9
42.4
The flue gas is recovered by a cyclone collector and then pumped into the combustion chamber. Air is added to the combustion chamber to convert arsenic sulfide, strontium sulfide, and elemental sulfur to oxide at 750 °C. These flue gases are cooled to approximately 350 ° C in a heat exchanger. As 2 O 3 and Sb 2 O 3 in the soot are removed by an electrostatic precipitator. The collected soot is transported to the material silo by the machinery at the bottom of the electrostatic precipitator, then wetted by water and transported to the market by truck. The flue gas discharged from the electrostatic precipitator is further cooled to 120 ° C, and the sublimated arsenic trioxide in the flue gas is recovered by a bag filter, and then packaged and sold to a chemical plant in the United States. The filtered harmless flue gas is discharged into the atmosphere through a chimney approximately 100 m from the factory.
In 1997, the mine installed a wet scrubber to further remove traces of As 2 O 3 and particulate matter from the flue gas. Studies have shown that when the bag filter is fully effective (80% to 96%), the recovery of arsenic can be increased from 95% to 98%.
Second, the arsenic treatment process of the Eltigne treatment plant
The plant processes smelting soot collected by the Caletones copper smelter through an electrostatic precipitator. The chemical composition of the soot is shown in Table 2.
Table 2 Chemical composition of soot obtained at the Eltnent factory
Cu T
Cu insol
As T
Fe T
Bi T
As ( m )
As ( v )
Fe 3 +
Mo
Sb
24.0
13.0
6.8
3.8
0.55
6.5
0.3
3.4
0.9
1.5
After obtaining the soot material, it was firstly pulverized with a solution rich in H 2 SO 4 from the El Teniente plant and then transported by special trucks to a special production line at the Eltnent factory for treatment. The specific processing process is divided into three phases:
(1) Acid leaching: At this stage, the soot slurry is leached with sulfuric acid at room temperature for 15 minutes to extract copper and arsenic. The leaching solution is transferred to the deposition treatment stage of arsenic.
(2) Leaching recovery é“‹ : The first stage solid matter was leached with a solution of NaCl (150 g/L) in H 2 SO 4 (40 g/L) for 60 minutes, and the liquid-solid ratio was 1.5:1. Then, to the leach slurry thickener to recover bismuth, copper, arsenic, and other metals from the overflow liquid. The solid material is washed on a thicker with a solution of sulfuric acid and SX plants and then recycled to the smelter. If economic conditions permit, helium can be recovered from the solution. If economic conditions do not allow, mix the mash in the first solution for further processing.
(III) Arsenic deposition: When no helium is recovered, add H 2 O 2 (12L/m 3 ) to the overflow liquid separated from the two thickeners, oxidize As(+3) to As(+5), and then add NaOH. the pH was adjusted to 3, followed by addition of iron sulfate to ferric arsenate arsenic deposited. The treated overflow is sent to a solvent extraction plant for copper extraction. Solid materials containing iron arsenate and antimony are landfilled as waste.
In addition, arsenic-containing emissions from the sulphuric acid plant are disposed of at the effluent treatment plant. The solution is neutralized, and arsenic is precipitated as calcium arsenite and calcium arsenate, and calcined to produce a stable product, Ca 3 (AsO 4 ) 2 .
3. Process for treating arsenic-containing soot in the Chuquicamata smelter
The Chuquicamata smelter also processes soot from copper smelters in a wet smelting plant to recover arsenic from copper and residues through a leaching process. Arsenic precipitates in the form of iron arsenate on site, as shown in Figure 2.
Figure 2 Process for removing arsenic-containing soot from the Chuquicamata smelter
In addition, the Chuquicamata smelter neutralizes the pH of the sulphuric acid-producing emissions to 12, allowing arsenic to precipitate as calcium arsenite CaAsO 2 (OH). The slurry is then transferred to a thickener, and treated with a clean water of pH 12, returned to the industrial water system, and the solid material is filtered and pressed to obtain a filter cake (50,000 m 3 /a). The filter cake contains 3% to 6% arsenic and 30% to 45% H 2 O, which is then transported to the slag yard by a dedicated truck, and is also used for copper arsenic removal at the Paipote, Chagres and Altonorte smelters in Chile.
4. Arsenic removal process at the Potre Rios smelter
The effluent from the sulphuric acid plant of the Potrerillos smelter (30 m 3 /h) contains 26 g/L H+ and 10 g/L arsenic. During the treatment, the pH was neutralized to 11 with a lime slurry, and arsenic was precipitated as calcium arsenite and calcium arsenate. The mud was thickened, filtered under the bottom stream, and a 40% moisture filter cake (4 t/h) was sent for further processing. The overflow pH of 100 ppm of arsenic was further neutralized to 8, and arsenic was precipitated as iron arsenate. The specific process flow is shown in Figure 3.
Figure 3 Arsenic removal process at the Potrerillos plant
The slurry is then sent to another thickener, filtered under the underflow, and passed through a sand filter to obtain an effluent containing less than 1 mg/L of arsenic.