Atmospheric pressure acid leaching
(A) Acid leaching reagent Atmospheric pressure acid leaching is the most commonly used leaching method. Sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, aqua regia and sulfurous acid can be used as leaching reagents for certain mineral raw materials, but the most common one is dilute sulfuric acid.
Dilute sulfuric acid is a weak oxidizing acid, which can process materials containing a large amount of reducing components. The immersion liquid can be purified and extracted by various methods, and the sulfuric acid is cheap and easy to obtain, the equipment is easy to solve corrosion, and the boiling point of sulfuric acid is high. Higher leaching temperatures can be used to achieve higher leaching speeds and leaching rates. Sulfuric acid leaching of oxide ores is the main agent, but also decomposition of carbonates, phosphates and certain sulfide minerals and other raw materials.
Hydrochloride with a variety of metals, metal oxides, metal sulfides and certain alkali soluble chloride generated which reactivity stronger than sulfuric acid, sulfuric acid can not leach leaching certain mineral salts of oxyacids. Hydrochloric acid may exhibit reductive or oxidizing properties depending on the specific conditions. However, its price is higher than that of sulfuric acid, it is volatile, its working conditions are poor, and its anti-corrosion requirements are high.
Nitric acid is a strong oxidizing acid with strong decomposition ability, but its price is high and equipment corrosion resistance is high. Nitric acid is generally not used alone as a leaching agent and is often used as an oxidizing agent.
Hydrofluoric acid is mainly used to leach germanium minerals and then extract useful components from hydrofluoric acid and sulfuric acid systems.
Aqua regia the platinum group metal is mainly used for leaching, platinum, palladium, gold salt into solution as a chloro complex, and rhodium, ruthenium, osmium, iridium, silver, etc. remain in the leaching residue, then separated by appropriate methods.
Medium strength sulphurous acid (or sulphur dioxide is introduced into the slurry) is a reducing agent; certain oxidizing materials can be leached to achieve higher leaching selectivity.
(Ii) simple atmospheric acid leaching into the leaching material a difficult job and calcine mineral feedstock, natural mineral mainly metal, sulfides, oxides and oxyacid salts like. These minerals can be directly dissolved in an acid, depending on its stability in an acid, can be used to measure pH ° T value, pH ° T. The higher the value the more easily the acid was dissolved. From the data in the bombardment, we can see that: (1) most of the metal oxides, ferrites , arsenates and silicates are soluble in the acid, and only FeS, NiS, CoS and MnS in the sulfides can be easily acid-soluble; 2) The ferrite, arsenate and silicate of the same metal are more stable than their simple oxides and are more difficult to be leached by acid. Therefore, the temperature must be strictly controlled during roasting to prevent the formation of the above salts; (3) with leaching As the temperature rises, the stability of the compound in the acid also increases accordingly, so when oxidizing mineral acid leaching, high temperature and high acid are often associated.
In practice, simple acid leaching is used to treat cobalt , nickel , zinc , copper , cadmium , manganese , phosphorus and other oxidized ore, oxidized baking sand and soot. The useful components are transferred into the solution, and the acidity can be properly controlled to achieve selective leaching.
When dilute sulfuric acid is leached, the free silica does not dissolve, and the bound silicic acid partially dissolves, and the amount of dissolution increases as the acidity and temperature increase. Aluminum oxide is more stable, a small amount of diluted sulfuric acid and dissolved. Stable iron oxide, ferrous oxide, but is easily decomposed sulfuric acid (40-50%) decompose carbonate, magnesium oxide, calcium, phosphorus-vanadium compound easily sulfate. Minerals such as rare earth, zirconium , titanium , niobium and tantalum are very stable. Copper, antimony , arsenic, chromium and other sulfides are also very stable, and the amount of dissolution in dilute sulfuric acid is extremely small.
The crude concentrate is sometimes removed some smaller impurity solubility sulfate, hydrochloric acid may be employed as the leaching agent, such as bismuth leaching with hydrochloric acid, calcium, phosphorus and molybdenum.
The reaction of aqua regia from platinum group metals is:
HNO 3 +3Hci=Ci 2 +NOCi+2H 2 O
Pt+2Ci 2 +2Hci=H 2 [PtCi 6 ]
Pd+2Ci 2 +2Hci=H 2 [PdCi 6 ]
Au+3Ci 2 +2Hci=2H[AuCi 4 ]
铑, 钌, 铱, 锇 and silver remain in the slag. The precious metal in the waste liquid can be recovered by the reduction of gold by ferrous sulfate, the precipitation of platinum by ammonium chloride, the palladium dichloride and the zinc precipitation method. [next]
(3) Oxidizing acid leaching
Metal sulfide minerals are relatively stable, and the ε-pH diagram of some MS-H 2 O systems is shown in Figure 1. When an oxidant is present, almost all of the sulfide is unstable over any pH range. At different pH values ​​and different potentials, sulfide minerals undergo the following four oxidation reactions:
(1) 2MS+O 2 +4H + =2M 2+ +2S+2H 2 O
(2) MS+2O 2 =M 2+ +SO 4 2-
(3) MS+2O 2 +2H 2 O=M(OH) 2 +SO 4 2- +2H +
(4) MS+2O 2 +2H 2 O=MO 2 2- +SO 4 2- +4H +
Without controlling the potential, the sulfur in the sulfide minerals will all be sulfated. In general, at low temperatures and low pH values, sulfide minerals are oxidized according to formula (1); at high temperatures and high pH values, sulfide minerals are oxidized according to formula (2). However, the upper limit of the pH of various sulfides in the formation of elemental sulfur in aqueous solution is different. The various sulfides are subjected to the standard potential of oxidation of the formula (1) and the pH of the elemental sulfur stable zone. The control potential and pH control the oxidation sequence of the sulfide mineral and the oxidation product of sulfur. [next]
In addition, some low-cost compounds such as UO 2 , Cu 2 S, Cu 2 O, etc., are also required to be oxidized to a high price before being dissolved in the acid. The ε-pH diagram of the UH 2 O system is shown in Fig. 2. UO 2 has a higher acidity required for direct acid dissolution of U 4 + , and is easily added if an oxidizing agent (such as ClO - 2 , Fe 3+ , MnO 2 , etc.) is added. Oxidation and transfer of UC 2 2+ ions into the solution. When the uranium ore is under normal pressure acid leaching, the concentration of uranium in the immersion liquid is about 1 g/L, which is equivalent to a uo 2 2+ =10 -2 . At this time, UO 2 2+ +2e=UO 2 reacts ε°=0.22 volts. , UO 2 2+ hydrolysis pH ° 298 = 3.5, therefore, uranium ore leaching often added 0.5 ~ 2.0% manganese dioxide weight, so that the reduction potential of the immersion liquid is 300 m volts, and should maintain a certain balance The acid makes the pH of the immersion liquid less than 3.5. If the uranium exists in the form of uranium trioxide, it does not need to be added with an oxidizing agent and can be directly dissolved in the dilute sulfuric acid solution.
When dilute sulfuric acid leaches out copper ore, secondary copper minerals such as malachite, azurite, sillimanite, chrysocolla, and copper blue can be directly acid-dissolved, and low-cost copper minerals (such as copper ore) It can be oxidized and acid soluble, and the dissolution rate of primary chalcopyrite and metallic copper in the presence of oxidant is also small. Therefore, dilute sulfuric acid is suitable for the treatment of secondary copper ore, especially copper mineral raw materials containing secondary copper oxide minerals.
Hot concentrated sulfuric acid is a strong oxidant, which can oxidize most sulfide minerals into sulfate: leaching sulphated slag with water, copper and iron entering the liquid, lead , silver, gold, antimony and the like remaining in the slag. At 200 ~ 250 ℃, hot concentrated sulfuric acid can break down some rare element minerals, such as lanthanum cerium phosphate ore, monazite, ilmenite and the like.
MS+2H 2 SO 4 =MSO 4 +SO 2 +S+2H 2 O
Nitric acid can be directly leached from molybdenum ore, copper, silver minerals, arsenic-containing sulfide ore and some rare elemental minerals. [next]
(4) Reducing acid leaching
The raw materials for reducing acid leaching are high-valent metal oxides or hydroxides, such as low-grade manganese ore, seabed manganese nodules, purified cobalt slag and manganese slag. The principle of reduction leaching is shown in Figure 3. Industrially, divalent iron ions, metallic iron, hydrochloric acid, and sulfur dioxide can be used as the leaching reagent.
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