Atmospheric alkali leaching

The alkali leaching reagents commonly used in the industry are ammonia, sodium carbonate, caustic soda, sodium sulfide, etc., which are described below.
(A) ammonia leaching NH 3 -CO 2 -H 2 O-based metal is an effective lixiviant copper, cobalt, nickel. The rate of leaching depends on the partial pressure of oxygen and the concentration of ammonia (Figure 1). The ε-pH diagrams of the cu-NH 3 -H 2 O system, the Ni-NH 3 -H 2 O system, the CO-NH 3 -H 2 O system, and the Fe-NH s -H 2 O system are shown in Figure 2, respectively. 3. As shown in Figure 4. It can be seen from the graph that when there is air, the stable region of Fe(NH 3 ) n 2+ is relatively small, and it is easily oxidized by oxygen to high-valent iron , and precipitates as hydroxide in the pH-10 lye. Therefore, the ammonia solution can selectively leach copper, cobalt, and nickel.

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Atmospheric ammonia leaching is an effective method for leaching metallic copper and copper oxide mineral raw materials. When the combined copper content in the ore is high, it should be pre-reduced and calcined to convert it into metallic copper and free copper oxide.
The ammonia leaching slurry is separated by solid-liquid separation, and the immersion liquid is sent to the ammonia. When the immersion liquid is heated to the boiling point (113-120 ° C), the ammonium carbonate and the ammonium ions are decomposed, the copper is precipitated as copper oxide, and the cobalt and nickel are respectively cobalt hydroxide. And basic nickel carbonate precipitated. The vapor containing ammonia and carbon dioxide is recovered by the condenser and returned to the leaching or washing operation.
At normal pressure ammonia leaching, the copper sulphide mineral is incompletely dissolved. The nickel, cobalt sulfide minerals and precious metals remain in the leaching residue. The copper, cobalt, nickel sulfide minerals and precious metals can be floated from the slag, and the flotation concentrate can be sent to smelting or It is treated by hot pressing ammonia leaching.
Ammonia leaching is characterized by selective leaching of metallic copper, cobalt, nickel and its oxidized ore. The immersion liquid is pure, the atmospheric pressure leaching speed is high, and the process of preparing the selected product and the reagent is simple. Therefore, the iron content is high and The copper-nickel mineral raw material mainly composed of carbonate gangue should be treated by ammonia leaching method, but the distillation tower is easy to be crusted when steaming ammonia, which affects the normal production. [next]
(2) The decomposition ability of the sodium carbonate solution leaching sodium carbonate solution is weaker than that of sulfuric acid, and the price is high, but the leaching selectivity is high and the immersion liquid is relatively pure. At present, it is widely used as a leaching agent for carbonate-type uranium ore, and can also leach tungsten mineral raw materials.
It can be seen from the above that sodium hydroxide is formed during leaching to increase the pH of the immersion liquid. The leaching of uranium with sodium carbonate is carried out under the condition of pH=9~10.5. When pH>10.5, the heavy uranium salt precipitates. Therefore, a mixture of sodium carbonate and sodium hydrogencarbonate is commonly used as a leaching agent in the production, and the amount of sodium hydrogencarbonate is usually 10-30% of the total amount of sodium carbonate solution immersed in uranium often under pressure (about 1013.25 kPa), the slurry The temperature is 100 to 150 ° C, the sodium carbonate concentration is 25 to 60 g / liter, and the sodium hydrogencarbonate is 5 to 25 g / liter.
In addition, the sodium carbonate solution can leach the tungsten mineral raw material, and the tungsten is transferred into the immersion liquid in the form of soluble sodium tungstate.
(C) leaching in caustic soda solution concentration of about 40 to 45% caustic soda solution can be directly leached galena, sphalerite, bauxite, wolfram, calcium tungstate and monazite ore, the corresponding object The components are transferred into a solution (or a precipitate). The copper-nickel sulfide ore is hot-pressed at 400 ° C to decompose the pyrite therein to obtain a copper-nickel sulfide ore concentrate.
At present, the caustic soda solution leaching is used to treat tungsten-containing minerals such as tungsten fine mud and tungsten- tin ore, which are high in silicon content, and is heated at normal pressure by a single caustic soda solution. Satisfactory leaching results were obtained at about 110 ° C or under pressure. Processing scheelite concentrates, caustic soda should be mixed with silicate reagent as a leaching agent. When a certain amount of silicon oxide is contained in the white tungsten raw material, a single caustic soda solution can be used as the leaching agent, and the reaction is:
CaWO 4 + SiO 2 + 2 NaOH = Na 2 WO 4 + CaSiO 3 + H 2 O
(4) Sodium sulfide solution Leaching sodium sulfide solution can decompose sulfide minerals of arsenic , antimony , tin and mercury to form corresponding soluble thioacid salts:
AS 2 S 3 +3Na 2 S=2Na 3 AsS 3
AS 2 S 5 +3Na 2 S=2Na 3 AsS 4
Sb 2 S 3 +3Na 2 S=2Na 3 SbS 3
Sb s5 +3Na 2 S=2Na 3 SbS 4
SnS 2 +Na 2 S=Na 2 SnS 3
HgS+Na 2 S=Na 2 HgS 2
Bi 2 O 3 and SnS are insoluble in the sodium sulfide solution. In order to prevent hydrolysis of sodium sulfide, a mixture of sodium sulfide and caustic soda is commonly used as a leaching reagent. This method can be used to remove impurities or extract relevant components from raw materials, such as removing arsenic from cobalt-nickel concentrate, and extracting tin and mercury from tin ore and cinnabar.

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