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Selection and calculation of carbon slurry equipment
According to the characteristics of the process, the main special equipment of the carbon pulp plant includes a carbon adsorption tank, a desorption column, an electrolysis tank and a carbon regeneration kiln. Due to the short history of production in China's carbon pulp mills, it is still in the stage of accumulating experience in equipment selection, design and calculation, and it is still to be summarized and improved.
Carbon adsorption tanks and leaching tanks can also be used as carbon adsorption tanks, but equipment with low carbon wear and low power consumption should be selected. Generally, a mechanical agitation tank with a double impeller hollow shaft inlet is used, and the calculation method is the same as that of the leaching tank.
In order to realize the reverse movement of the slurry and the carbon, an intermediate sieve is arranged in the adsorption tank. Its role is to separate the slurry from the activated carbon. In the country, a fixed bridge sieve is generally used. The length of the screen can be calculated according to the amount of pulp that the adsorption tank passes. Generally, the amount of slurry passing through the screen per unit length is 6.5L/(m·s).
To prevent clogging, bridge screens require low pressure air to clean the screen surface. The low pressure wind gauge indicates a pressure of 35 kPa, and the low pressure air volume required per unit length of the screen is 1.0 m 3 /(m·min).
The desorption column and the desorption method of gold- cut carbon are many. In China, high-concentration sodium cyanide (temperature is 95 ° C) is used for desorption in the desorption column. The desorption column is usually designed as a cylinder. The ratio of the height Ho of the carbon bed to the diameter D is 6:1, the flow rate of the desorbing solution should be less than 3.4 m/s, and the flow rate (m 3 /h) is generally the volume of two carbon beds. So that the char does not flow. The diameter and height of the desired desorption column can be calculated according to the above conditions based on the amount of carbon cuts required to desorb each day. The flow rate check is then performed on the selected desorption column. The technical performance of the desorption column is shown in Table 1.
Table 1 Desorption column technical performance
Specifications / mm
Volume / m 3
Design pressure / kPa (kg / cm 2 )
Design temperature / °C
900900×4200
3
490 (5.0)
135
700700×3800
1.5
245 (2.5)
100
500500×2500
0.5
98
In the electrolytic cell, the noble liquid after desorption of gold-loaded carbon is often subjected to electrodeposition to obtain high-grade gold mud. The equipment used is the electrolytic cell. The main parameters are: current density, solution temperature, flow rate and tank voltage. Under normal conditions, the current density determines the rate of deposition and deposition of the cathode metal. A current density of 20 to 50 A/m 2 is usually used. Practice has shown that the current density increases from 20 A/m 2 to 60 A/m 2 . The deposition rate of noble metal at the cathode is proportional to the increase of current density. When the current density exceeds 60 A/m 2 , the current efficiency appears. Drops and greatly increases the consumption of electrical energy and anode and cathode materials. Properly increasing the current density, solution temperature and flow rate can increase the deposition rate of gold. The potential for gold to precipitate at the cathode under normal conditions is +0.2V.
The electrolysis cell is generally designed and selected according to the gold content and the electrowinning time in the noble liquid. The technical performance of the gold electrolyzer is shown in Table 2.
Table 2 Technical performance of gold electrolyzer
Specification length × width × height mm
Cathode plate size / mm
Cathode plate spacing / mm
Number of cathode plates
Cathode plate size / mm
Cathode plate spacing / mm
Number of cathode plates
Amount of electrolyte / L
Electrolyte flow rate / L / s
Electrolyte temperature / °C
Cathode plate current density / A · m -2
Current intensity / A
Voltage / V
2440×750×610
620×610
111
20
620×610
111
twenty one
1116
0.45
120
53.8
1000
1.5~3
Calculation example: Electrolytic treatment of gold-loaded carbon desorbing precious liquid V G = 1000L / d, its grade β = 81g / L, power-on time t = 24h, calculate the required electrolytic cell size.
According to the current operating experience, the cathode plate current density Ï 1 = 40A/m 2 ; the cathode plate current efficiency η = 90%; the cell voltage 3V; the gold electrochemical equivalent j = 7.359 / (A · h).
(1) Calculate the required total current amount I from m = jItη.
Where m is the amount of electrolytic gold, g.
m=V G β
I=V G β/(Jtη)=[81000/(7.35×24×0.9)]A=510.2A
(2) Calculate the total area of ​​the cathode plate according to the current density of the cathode plate.
A=I/Ï I = (510.2/40) m 2 = 12.8 m 2
(3) DC power consumption per kilogram of gold.
W=V×10 3 /(jη)
W/kW·h=3×10 3 /(7.35×0.9)=454
According to the above data, the cell size is 2440×750×610, which can satisfy the total area of ​​the cathode plate of 15m 2 . If there is no suitable cell, it can be designed according to the above data.
In the carbon regeneration kiln, the carbon particles are also adsorbed with various inorganic substances and organic substances during the adsorption process of the carbon slurry. After desorption, they cannot be removed, pollute the carbon particles, and reduce the adsorption activity. Therefore, it must be regenerated before returning to use. The regeneration is carried out in two steps: removal of the calcium carbonate and most of the base metal complex by pickling; heat activation to remove other inorganic and organic impurities. The heating activation is to insulate the air in the rotary kiln and heat the carbon to 650~750 °C for 30 min, then quench it by water, sieve out the fine charcoal (<20 mesh) and return it for reuse. At present, there are two kinds of carbon regeneration kiln used in domestic carbon pulp factory: one is TS-20 rotary regenerative kiln, the processing capacity is 20kg/h, and the other is direct heating rotary kiln of Beijing Nonferrous Metals Design and Research Institute. , the specification ф460×5800, the feeding amount is 0.47kg/s (wet material 0.94kg/s).