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1. Basic principles
Neutralization tank dissolution of copper is a solid liquid gas three-phase chemical reaction
Cu+1/2O2+H2SO4=CuSO4+H2O
According to the principles of kinetics, the following aspects are effective measures to improve the chemical reaction rate of copper dissolution: (1) increasing the chemical reaction surface area of copper material.
This requires the physical size of copper material to be as small as possible;
(2) Strengthen stirring to enable copper material to flow with the solution and form a fluidized bed conducive to solute diffusion;
(3) Higher concentrations of H2SO4 and O2, reaction temperature, and increased catalyst.
However, due to production process limitations, the most practical measure among the above measures is to increase the concentration of O2 in the solution.
As is well known, to increase the concentration of oxygen in a solution, it is necessary to increase the air flow or increase the contact area between air and the solution.
The problem with conventional neutralization tanks is that compressed air is usually injected into the solution through several conduits to oxygenate the solution. Practice has shown that the air entering the solution through the conduits often forms large bubbles, which prematurely escape from the liquid surface without sufficient contact with the solution, resulting in extremely low oxygen utilization efficiency.
Increasing the number of ducts or air volume is not ideal, as it not only increases energy consumption but also causes many adverse consequences such as solution loss and harsh environment.
Therefore, people are trying to find ways to make air form small bubbles in solution.
Following the above approach, a domestic factory has made improvements to the oxygen supply method for the neutralization tank.
The main method is to add an air distribution plate at the bottom of the neutralization tank, allowing air to enter the solution through the small holes on the distribution plate.
Undoubtedly, due to the dispersing effect of the small holes on the air, the air entering the solution forms small bubbles, which slows down the speed of air escaping from the liquid surface and increases the chance of contact between the air and the solution. After the transformation, the copper dissolution rate of the neutralization tank using waste copper wire as raw material reached over 85kg/m3 · d, which is nearly 30% higher than before the transformation.
Further reducing the diameter of the small holes in the air distribution plate is beneficial for the formation of smaller air bubbles, but this measure will encounter the problem of frequent blockage of the small holes, which is not conducive to the stable production of the equipment.
2. Important improvements to the new neutralization tank
Generally speaking, the oxygenation effect of small bubbles is better than that of large bubbles. Can we find a method to further improve the oxygenation effect of microbubbles?
Figure 1 is a schematic diagram of the structure of a novel neutralization tank for microbubble oxygenation.
The new neutralization tank, like the conventional tank, has parts such as a reactor and a false bottom.
The new type of neutralization tank uses the lower part of the false bottom as a gas-liquid separator, and adds two major components that are different from conventional neutralization tanks, namely a circulation pump and a liquid gas jet pump.
The use of a liquid gas jet pump to emulsify and mix gas and liquid under certain conditions is an important change in the new oxygenation method for neutralization tanks.
In working condition, the circulating pump sucks in the solution from the bottom of the gas-liquid separator and sends it to the liquid gas jet pump. At the jet pump nozzle, the solution is sprayed out at a speed of * * m/s or above.
The new neutralization tank can work intermittently or continuously.
When continuous operation is required, pre molten copper can be injected into the replenishment port of the neutralization tank, and qualified post molten copper can be discharged to the next process through the overflow port.
It is obvious that the gas-liquid contact interface of emulsified mixed oxygenation is much larger than that of large bubble oxygenation, and the residence time of microbubbles in the solution is also longer. When the chemical reaction causes the oxygen concentration of the local solution to decrease, the oxygen in the microbubbles can be replenished at any time, ensuring that the oxidation potential of the solution is always at a high level, which plays a key role in improving the copper dissolution rate.
In addition, when microbubbles with decreased oxygen content reach the vicinity of the page, they can form a continuous phase of small bubbles, which can suppress acid mist and reduce the heat loss caused by solution evaporation, which is beneficial for environmental protection and establishing thermal balance.
Tests have shown that the utilization rate of oxygen in the new neutralization tank can generally reach over 30%, so the new neutralization tank no longer requires excessive air supply.
3. Practical application
When processing copper materials with larger physical dimensions in the new neutralization tank, it is also necessary to require the copper material to have sufficient chemical reaction surface area. This can only be achieved by increasing the feeding amount, so the size of the reactor chamber is also important.
Experiments have shown that for every kilowatt of power of the circulating pump motor, the volume of the reactor chamber should generally be above 0.2-0.25m3;
In order to ensure the emulsification effect, the head of the circulating pump should be 30-40m; the volume of the gas-liquid separator should also be large enough to prevent poor gas separation from causing cavitation of the circulating pump.
Application 1: Copper dissolution process of pentahydrate copper sulfate.
The reactor volume is 4m3, with a height to diameter ratio of 1:0.75, equipped with an 18.5kw circulating pump, a head of 35m, a flow rate of 60m3/h, a gas-liquid separator volume of about 1m3, and equipment dimensions of 2.1m * 1.8m * 4.5m (excluding chimney).
Using waste copper wire as raw material, the solution before copper dissolution contains Cu2+60g/L and H2SO4 70g/L, and the solution after copper dissolution contains Cu2+170g/L and H2SO4 70g/L, with a self heating operation at around 80 ° C. The copper dissolution rate is as high as 375kg/m3 · d, which is more than four times higher than that of conventional neutralization tanks. The daily production of copper sulfate pentahydrate products is about 6 tons.
The comprehensive electricity consumption of copper sulfate products is about 130kWh/t, and the H2SO4 content in the exhaust gas is less than 60mg/m3. As the equipment can self heat and self supply oxygen, the factory no longer needs to equip peripheral equipment such as boilers and air compressors, which greatly saves investment.
Application 2: Copper dissolution process for producing electrolytic copper foil, using bright copper rods with a diameter of 15mm and a length of 300-500mm or electrolytic copper strips with a diameter of 400mm * 20mm * 10mm. The copper dissolution rate has been increased from 36kg/m3 · d in conventional neutralization tanks to around 300kg/m3 · d, which is more than 7 times faster.
It should be pointed out that the amount of air used in the new neutralization tank is only one tenth of that in the conventional neutralization tank, which can reduce the possible pollution of the solution caused by impurities in the air. This is extremely beneficial for enterprises producing high-end electrolytic copper foil.
The new neutralization tank is equipped with one or multiple stages of cyclones for solid-liquid separation and auxiliary components for separating insoluble substances such as oil stains. Therefore, the new neutralization tank can also process powdered copper materials with a copper dissolution rate of about 500kg/m3 · d, achieving multi-purpose use of one machine.
4. Conclusion
The new neutralization tank adopts the oxygen supply method of gas-liquid emulsion mixing, greatly improving the copper dissolution rate and enabling self heating operation.
The stable operation of the new neutralization tank requires the circulating water pump to be resistant to corrosion, high temperature, wear, and crystallization.
