B. Technical control of the leaching process The technical control of the leaching process has three main aspects: neutral leaching end point control, leaching process balance control, and leaching technical condition control. The working space of the concentration tank can generally be divided into a clarification zone (A zone), a free sedimentation zone (B zone), a filtration zone (C zone), a compression zone (D zone), and a concentration zone (E zone). The zinc leaching suspension first enters the B zone, and the solid particles settle into the human filtration zone (C zone). In the filtration zone, some of the particles settle by themselves, while another part of the particles are entrained by dense particles and then enter the compression zone (D Area). Solid Incinerator, Marine Incinerator, Marine Waste Incinerators Fuente International Co., Ltd. , http://www.shipssp.com
When the neutral leaching, the control end point pH value is 5.2~5.4, so that the ferric iron is hydrolyzed by Fe(OH) 3 and aggregates and settles together with impurities such as silicon, arsenic , antimony and bismuth , so that the slurry sedimentation speed is fast and the solution is well purified. purpose. Of corporate wet zinc smelting production practice long-term control of the neutral leaching end accumulated experience, the pH of the slurry master leaching ore gradually increased, a trivalent iron hydroxide, and silicic acid particles in the solution spontaneously, cohesion becomes Large process characteristics, based on which to accurately control the endpoint pH. [next]
The solution system of the wet zinc smelting process is a closed circuit, so the volume of the solution in the system, the amount of zinc and the volume of the concentrated mud after the clarification and concentration of the slurry are fixed, that is, the so-called water balance (solution volume balance), zinc balance, and slag are generally called. Balance is of great importance to the stable operation and the technical conditions of the stable production process. And pay attention to the intake and discharge of water, zinc and slag.
The quality of the leaching process is closely related to the selected technical conditions. Practice has shown that only good selection of operating technical conditions and strict operation can achieve good leaching results.
A neutral leaching is the key to the leaching process and directly affects the quality of the leached pulp. As long as the technical conditions are selected correctly and the leaching end point is controlled accurately, a high quality leaching solution with fast sedimentation speed, easy clarification filtration, low impurity content and low suspended matter can be obtained. Each factory should determine technical conditions based on specific conditions, such as:
Continuous neutral leaching technical conditions Leaching temperature 60～75 °C
Leachate solid ratio (mass ratio of leachate to feed) (10~15): 1
Leaching acid 30~40g/L
Leaching terminal acid (last leaching tank outlet) PH=5.0～5.2 (If there is less reflux in the leaching process, more acid in the tank, the pH value of the end point can be lower, take the lower limit)
Leaching time (dwelling time in the tank) 1~2h
Continuous acid leaching technical conditions Leaching temperature 60 ~ 80 °C
Leachate solid ratio (7 ~ 9): 1
Leaching terminal acid pH=2.5 ～ 3.5
Leaching start acid 80～120g/L
Leaching time 2 ~ 2.5h
C Concentration and Filtration of Leaching Slurry Gravity concentration is the initial separation of suspended solids from liquids by solid particles in the suspension that settle by gravity.
In the concentration process, not only the coarse fraction is easy to settle, but the fine fraction can also achieve good sedimentation effect by agglomeration, and gravity concentration is usually carried out by a concentration tank. The sedimentation process of the slurry in the concentration tank is shown in the figure below. [next]
The solid particles in the suspension zone have formed a tighter floc, and although the floc continues to settle, the velocity has slowed down and then enters the concentrate zone (zone E). In this area, due to the movement and extrusion of the squeegee of the concentration tank, the concentration of the concentrated mud is further increased, and finally discharged from the bottom of the concentrator. The supernatant obtained by concentration is discharged as a liquid-solid separation product from the weir, and sent to the next step for treatment.
Commonly used filtration methods for wet zinc smelting are: vacuum filtration, the driving force is a vacuum source, commonly used vacuum degree 53 ~ 90kPa and pressure filtration, the driving force is usually provided by a pressure pump, the pressure is generally 80 ~ 200kPa. In industrial production, different filtration methods and filtration equipment can be selected according to different conditions and requirements.
The hot acid leaching zinc roasting ore thermal acid leaching method was developed in the late 1960s with the successful development of various iron removal methods. Since the zinc ferrite is decomposed, the iron entering the solution can be effectively separated from the zinc solution by the jarosite method, the goethite method or the hematite method, so that the calcined hot acid leaching method is widely used.
The essence of the hot acid leaching process is to leaching the slag of the zinc roasting ore by neutral leaching with high temperature and high acid, in order to dissolve the zinc ferrite which has not been dissolved in the low acid and a small amount of other undissolved zinc compounds, thereby further improving Zinc leaching rate. The hot acid leaching is to increase the high temperature and high acid leaching section on the basis of the original conventional leaching method, so that the leaching process becomes a leaching process with different acidity and multi-stage countercurrent. It is characterized by a gradual increase in the acidity of the leaching and a decrease in the amount of leaching slag. Finally, the valuable metals such as lead , silver and gold in the leaching residue are greatly enriched, which facilitates further recovery of these metals.
The hot acid leaching rate is high, and the leaching rate of the two-stage hot acid leaching zinc can reach 99%. At present, the hot acid leaching process at home and abroad is different because of the different conditions of each manufacturer and the different ways of removing iron. The hot acid leaching process of each factory is also different. The hot acid leaching process can be divided into a thermal acid leaching process and a multi-stage thermal acid leaching process according to the number of leaching stages.