Widely used in chemical processing metal Replacement recovering useful components from the immersion liquid, for fractionation and purification to remove certain impurities. Metal replacement is a redox process in which a metal displaces another metal ion from solution. At this time, the metal as a displacer is oxidized into an ion form and enters the solution, and the replaced metal ion is reduced to a metallic state.
For example, the reaction of iron to replace copper is:
Cu 2+ +Fe —— Cu+Fe 2
The main factors affecting the metal replacement process are as follows:
1
(1) The effect of oxygen in the solution. Oxygen is a strong oxidant that oxidizes many metals into ions, such as: Zn+—O 2 +2H + ==== Zn 2+ +H 2 O
2
Thus, the oxygen-containing solution will consume zinc, gold and silver cyanide solution when using zinc substitution method, the solution should be replaced before the deoxidation (2) was dissolved tuck effect of pH. For example, iron sinking copper should be carried out under the condition of pH=1.5~2.0. If the acidity is too high, the iron scrap consumption will increase. However, the acidity should not be too low, otherwise it will cause the hydrolysis of iron salt to reduce the grade of copper mud, and the final pH is ≤4.5. The displacement rate increases with the increase of acidity; when the pH is less than 1.5, the porous precipitate is formed, and the adhesion is weak; when the pH is less than 1.5, the reaction speed is less affected.
(3) The influence of the concentration of the displaced metal ions. It mainly affects the physical properties and reaction speed of sediments. When the concentration is high, a dense adhering precipitate is formed on the surface of the displacer, which is not easy to be peeled off; when the concentration is low, a porous precipitate is easily formed, which is easy to peel off.
(4) Temperature influence. The temperature can promote the progress of the displacement reaction, and the production is generally carried out at normal temperature.
(5) The larger the difference between the potential difference between the displacer and the metal to be replaced, the more complete the substitution.
(6) The influence of other components in the solution. When substituted, such as iron, copper, iron loss increases when a high content of Fe 3+ in the solution, then it may be returned for leaching or reduction with sulfur dioxide which is reduced to reduce the high iron content of the solution; if the arsenic containing solution Copper arsenic and highly toxic hydrogen arsenic gases are formed:
2As 3+ +3Fe ==== 2As+3Fe 2+
H 3 AsO 3 +2H 2 SO 4 +3Fe ==== AsH 3 ↑+3FeSO 4 +3H 2 O
3H 2 SO 4 +Fe(As) 2 +2Fe ==== 2AsH 3 ↑+3FeSO 4
3H 2 SO 4 +H 3 AsO 3 +2Al ==== AsH 3 ↑+Al 2 (SO 4 ) 3 +3H 2 O
It can be seen from the above reaction formula that Fe(As) 2 and aluminum shavings should not be mixed in the iron filings.
(7) The increase in the solution flow rate or the stirring strength can reduce the thickness of the diffusion layer and facilitate the renewal of the surface of the displacer, and accelerate the progress of the displacement reaction.
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