Pretreatment process of refractory ore and concentrate - pressurized oxidative decomposition

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The pressurized oxidative decomposition method is a commonly used method for oxidizing desulfurization and sulfur. It can be used to treat ore and can also be used to treat concentrates. It can be carried out in an acidic or alkaline medium or in a neutral medium. Among them, acidic media is widely used in industry. Although alkaline medium leaching has the advantages of low operating temperature, light corrosion of equipment, and oxidation of Fe into Fe 2 O 3 into the slag, S and As are dissolved and soluble Na 2 SO 4 and Na 3 AsO 4 are formed . Especially difficult to handle with Na 3 AsO 4 . And the use of alkaline medium, the reagent NaOH price is high and expensive, if the raw materials have Hg and Tl in the past, they will release their pollutants.

1. Pressurized acid leaching oxidation method

The operating conditions of the pressurized acid leaching pre-oxidation treatment of the refractory arsenic gold concentrate are mostly reported in the literature at a temperature of 80 to 200 ° C (mostly at 170 to 180 ° C) and a pressure of 5 to 10 atm (500 to 1010 kPa). Only the report of Little Agar is 22atm (2229kPa).

The pressure acid leaching oxidation method studied in detail by Sherritt Gordon of Canada is 170 ° C with a dilute sulfuric acid solution at a temperature higher than the melting point of S ° (118 ° C) (it is also suggested to be lower than 118 ° C) And oxygen pressure 8 ~ 10 atm (810 ~ 1010kPa), leached in a titanium autoclave. It allows pyrite and arsenopyrite to achieve complete oxidation, during the generation amount S ° and the temperature. If the temperature is raised to 180 to 190 ° C, it is possible to completely remove S °.

The above leaching reaction kinetics, the reaction speed of arsenopyrite is faster than that of pyrite. Although the reaction in the process is complicated, the final products are mainly sulfuric acid, hematite and scorodite (FeAsO 4 ·2H 2 O or Fe 2 O 3 ·As 2 O 5 ·4H 2 O). The scorodite is a stable crystal of iron arsenate. In hydrometallurgy, this method is the only one that can form arsenic to form crystalline iron arsenate. However, there are also concerns that the formation of iron arsenate is less stable and has the potential to release arsenic, and this method will reduce the recovery rate of symbiotic silver . Although the silver dissolves into the solution during the process, most of it is precipitated together with the produced jarosite, which makes the silver once again difficult to dip. To recover silver from this precipitate, it is recommended to add a hot lime solution to decompose the jarosite before the next leaching to release the silver. This process must be leached for 2 hours at a temperature of 90 ° C and a consumption of 20 to 100 kg of slaked lime per ton of concentrate. Therefore, this process is difficult to obtain the approval of the manufacturer.

The pressurized acid leaching process can not only effectively treat high-sulfur gold concentrate, even if only 4% to 5% of the ore containing sulfur is sufficient to achieve its own oxidation. The harmful impurities such as Sb and Pb are less affected, and the recovery rate of gold is generally high. In the production costs, oxidation costs account for 60%, and neutralization costs account for about 25%.

The first manufacturer to apply this process was Homestake's McLaughlin plant, which used it to process ore. The second manufacturer was the Saabento plant in Brazil, which was commissioned in 1986 to treat concentrates. Since then, METBA has chosen this process to treat the arsenic-containing pyrite concentrate from Olympias, Greece. The Sheridan Gordon Engineering Company of Canada designed a pressurized oxidation plant for the Porgera plant in Papua New Guinea.

An improved process for pressurized acid leaching is a 1981 patent from Arseno Mining and Metallurgy Co., Canada, also known as the Aceno method or the nitration process. The improved process is a low temperature pressure oxidation process which can be carried out at 80 to 200 ° C and an oxygen pressure of 500 kPa, a solid-liquid ratio of 1:6, and a total acidity of 3 mol/L (wherein HNO 2 is 0.5 to 3 mol ∕L). The leaching medium is changed to a mixed acid of H 2 SO 4 and HNO 2 (or HNO 3 ), which has a strong oxidizing ability, and the coarser material can be processed without being finely ground. Nitrous acid in the process is an oxidation catalyst for decomposing minerals, and NO generated by the reaction can be regenerated in situ in the gas phase by O 2 . Due to the catalytic action of HNO 2 , pyrite and arsenopyrite can be completely oxidized within 15 min. Since the oxidation time is extremely short, all the sulfates, Fe, S, and As in the raw materials remain in the solution without precipitation. Silver does not precipitate with the ferropotassium vanadium as described in the previous method and causes losses. The oxidized slag produced by the pretreatment after this method is subjected to cyanidation leaching, and the leaching rate of gold is more than 93%. If this method is used for continuous production, it is more suitable to use two stages (15 minutes each) for autoclave leaching. However, because the reaction process is so fast, the most suitable equipment is the 310 or 304L stainless steel pipe dissolver from Lurgi Chemical Metallurgy Co., Ltd., without using a titanium autoclave to reduce cost, facilitate heat dissipation and facilitate operation. The disadvantage of this method is that S° may be generated in the process to make filtration difficult and is not conducive to cyanide leaching of gold, and a cooling system is required to reduce the excessive heat generated by the reaction process.

The process was planned for a plant in south-central British Columbia to process a 15t∕d wet concentrate. The oxidized slag after leaching of the concentrate is sent to cyanide. The silver in the immersion liquid is recovered by sodium thiocyanate precipitation, and the As, Fe, S and lime are neutralized and heated in a stainless steel autoclave to produce iron arsenate, hematite and gypsum discharged into the tailings dam. The tail liquid is returned for use.

According to the Aseno method, since oxygen is supplied in a solution containing HNO 2 or HNO 3 at 80 ° C or higher, As, Fe, S, Cu, Ag, etc. contained in the ore or concentrate are not only oxidized quickly, but also Within 2 to 30 minutes, 90% of their content can be decomposed into the solution, and the oxidized slag is mainly composed of Au, gangue and S°. If the concentrate is treated, the weight loss rate of the concentrate can be up to 90%, and the material to be cyanated only accounts for more than 10% of the concentrate. The solid-liquid separation of the slurry can be completed by using a filter, and gold is cyanide. The recovery rate of silver is also high. Taking the White Doug Flotation Plant in Papua New Guinea as an example, the concentrate contains Au, 62g ∕t, Ag 306g ∕t, S 29.8%, Cu 7.36%, and the leaching rate of direct cyanide Au is only 23.3%. The oxidation leaching rates of Cu, Fe, S, Ag and Au were 80.6%, 95.3%, 90.6% and 89.1%, respectively, after pretreatment for 30 min at a temperature of 100 ° C and a solution containing HNO 3 180 g∕t and a slurry concentration of 15%. And 3.5%. After cyanidation of the oxidized slag, the total proposed ratio of gold and silver in the concentrate is 92% and 97%.

When the low-sulfur (1.6%) gold ore is treated by the Aseno process, the reaction can still proceed spontaneously and can be carried out at atmospheric pressure and at lower temperatures. Only the denitration process requires steam. The slurry after the oxidation reaction does not have to be subjected to solid-liquid separation, and cyanide can be sent after the lime is neutralized. For example, the St. Nalle gold mine in Canada contains Au 2g∕t and FeS 2 2% to 3%. After fine grinding and cyanidation, the gold leaching rate is only 32% to 66%. The expansion test was carried out by the Asenol method, and immersed in four mechanical stirring tanks (oxygen supplied to the first tank, oxygen pressure is not too high and relied on NO oxidation) at 70-80 ° C and atmospheric pressure for 2 h, FeS 2 95% is oxidized. After the operation was terminated, the liquid contained NO 3 - only 1.5 g ∕L. The pulp is first added with limestone , then cyanized after neutralization with lime, and the gold leaching rate is higher than 90%. Feasibility study on the construction of a 6000t/d large-scale plant based on the expanded test results shows that the total investment is 48 million Canadian dollars, which is the McLaughlin 3000t/d factory designed by Sheridan Gordon Company using high temperature and high pressure oxygen leaching. A total investment of 90 million US dollars is much more economical.

The united gold mine is a gold-bearing iron ore deposit, and the gold particles are submerged in a micro-scale disseminated form in pyrite. The test concentrate contains S 22.84%, Fe 21.86%, Au 46.3 g∕t, Ag 43 g/t. The ore is made of all mud cyanide, and the recovery rate of gold is only 75%. In order to improve the recovery rate of gold and select the best process, the Institute of Chemical and Metallurgy of the Chinese Academy of Sciences has carried out a pressurized acid leaching pretreatment expansion test on its flotation concentrate, which removes most of the sulfur by oxidation to make the gold particles from the pyrite. After dissociation, send cyanide.

The test was carried out in an enamel reactor (the stainless steel reactor was changed during production), and the operating conditions were tested in multiple schemes, with 47 to 50 # ore samples being the best. That is, the flotation concentrate used has a particle size of 99% - 320 mesh, and is first slurried with an aqueous solution containing sodium lignin sulfonate 0.2 g ∕L, H 2 SO 4 28 g ∕L and stirred for 0.5 h to discharge the CO 2 formed by the reaction. Add to the reaction vessel, add HNO 3 and add water to the solid-liquid ratio of 1:4 ~ 5, H 2 SO 4 0.15mol ∕L, HNO 3 0.12mol / L, sodium lignin sulfonate 0.1g ∕L, will The lid of the kettle lid is heated to 100 ° C, and then oxygen is introduced, and the mixture is leached for 2 to 3 hours. The pressure in the autoclave was maintained at 404 kPa during the process. After leaching, the slag containing S falls to 6.25% to 13.0% (including S° 4.7% to 5.8%), and after the lime treatment, the slag contains S° down to 2.9% to 4.0% for cyanidation. The cyanide method uses a carbon slurry method, and the leaching rate of gold is stabilized at 95% or more. After the gold leaching, the slag still contains S°2.2% to 3.2%, which indicates that a high gold cyanide leaching rate can be obtained without complete desulfurization. Oxidation leachate and wash solution can also reduce acid consumption, and excess waste liquid is neutralized with limestone and lime.

Second, pressurized alkali immersion oxidation

The United States Mining Authority (USBM) Reno Metallurgical Research Center specializes in hydrometallurgy of Au, Ag, Cu, Hg and rare earth metals and alloys. When it treated the arsenic-containing gold concentrate by wet method, it was found that gold in a few arsenic concentrates could be directly leached by cyanidation. For those that cannot be directly leached by cyanidation, they are pre-oxidized and leached for 5-20 hours in a titanium reactor at 1013 kPa and 105 °C with limestone and oxygen supply, and then the oxidized slag is cyanated or thiourea leached. The leaching rate of gold is more than 90%. The filtrate was added with NaI to precipitate Ag in AgI and returned to the leaching. In order to save investment, this method can use a low carbon steel or stainless steel reactor without the use of titanium.

3. Pressurized neutral leaching oxidation method

This method is a neutral pressurized oxidation pretreatment plant designed by Wright Engineering in Canada for two carbon-bearing pyrite gold deposits in Mercur, Utah, and Getchell, Nevada. The two plants are 750t∕d and 3000t/d ore respectively. The leaching operation was carried out at 225 ° C and pH 7-8 without reagents.

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