The zinc sulfide concentrate of Huludao Zinc Plant in China adopts high temperature roasting process. The high-temperature dust collected by the high-temperature electric dust collection and the soot collected by the secondary roasting of the rotary kiln and the double-blind ash and electric dust collected by the zinc concentrate of the first, second and fourth smelters of Shuikoushan Mining Bureau are high in cadmium. It is the raw material for cadmium. The components of this cadmium-containing soot are listed in Table 1.
Table 1 Composition of cadmium-containing soot
category | Zn | Cd | Pb | Cu | As | Fe | Ss | Sso 4 |
High temperature dust | 40± | 5~6 | 4~5 | - | - | - | - | - |
Cadmium dust | 18~20 | 18~23 | - | - | - | - | - | - |
Double ash | 47～52 | 0.8 to 1.1 | 6~12 | 0.4 to 0.7 | 0.2 to 0.8 | 11~13 | 1 to 2 | 2 to 4 |
Electric dust | 35～40 | 2 to 4 | 15~25 | 0.2 to 0.3 | 0.3 to 1 | 0.3 to 1.2 | 1.2 to 3 | 2 to 4 |
The third smelter of Shuikoushan Mining Bureau uses the all-wet process to treat the soot. The basic process is similar to the electrowinning process of Cu-Cd slag. The recovery rate of cadmium smelting is 88.75%, and the grade of cadmium is 99.99%.
The Huludao Zinc Plant uses a wet-fire combined process to treat cadmium-containing soot. The production process is shown in Figure 1. The main advantage of this method is a simple process, high metal recoveries, the total recovery of cadmium in 1980 reached 71.29 percent, higher product quality, purity cadmium refined output stable at 99.995%.
Figure 1 Huludao zinc plant extracts cadmium from soot
The plant successfully tested the crude cadmium refining process in 1958. The cadmium rectification tower has a height of 5.585m and consists of 28 trays with a tray size of 360×250mm. The technical conditions for rectification are as follows:
Enter the furnace crude cadmium grade /% 98 ~ 99
Combustion chamber temperature / K 1343 ~ 1353
Bottom temperature / K 1313 ~ 1323
Upper temperature / K 893 ~ 913
Gas condenser temperature / K 953 ~ 973
Liquid condenser temperature / K 843 ~ 863
Feeder temperature / K 773 ~ 823
Fine cadmium pot temperature / K 753 ~ 773
Crude cadmium melting pot temperature / K 723 ~ 773
Unit heating surface productivity / (kg · (m 2 · d) -1 ) 965 ~ 980
Cadmium recovery rate /% >99.7
Direct production rate of cadmium /% >98
Production of 1t cadmium consumption /%
Caustic soda / kg 12 ~ 14
Coal / kg 650 ~ 700
Water / t 1.5 ~ 2
The cadmium slag component discharged from the bottom of the column is: 70% to 72% Cd, 13% to 15% Pb, 0.02% to 1.08% Zn, 3.1% to 4.6% Cu, 2.1% to 3.1% Fe, 3.5% to 4.9% As , 0.1% to 0.2% T1. This slag is sent to the recovery tank .
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