A decade’s Production Practice of JCC Kivcet Technique

This article provides an overview of the Kivcet technique in Jiangxi Copper Corporation, reviews the production status and problems encountered in the past decade, introduces its technological advantages and prospect. It is believed that the Kivcet process has advantages such as strong adaptability to raw materials, stable operation, high metal recovery rate, and low cost of zinc leaching residue treatment, which is the vitality of lead-zinc smelting enterprises in the future.


Introduction
At the beginning of the 21st century, large-sized integrated nonferrous metal smelting enterprises named Jiangxi Copper Group Co., Ltd., based on its "Relevant Diversification" development strategy, established an integrated lead and zinc smelting plant in Hukou county, Jiujiang city, Jiangxi province in 2009.The group launched a 200,000 t/a integrated lead and zinc smelting and comprehensive utilization of lead-zinc bearing material project, its annual production includes 100,000 t/a lead and 100,000 t/a zinc.The lead smelter utilizes Kivcet lead material direct smelting process, the zinc smelter utilizes conventional hydrometallurgical zinc production process [1][2][3] with advanced automation technique, such as automatic zinc stripping machine [4][5][6][7] .The project was completed and put into operation in the first quarter of 2011.
The project apply an integrated lead and zinc smelting process: the lead smelter processes the leaching residue of zinc smelter with Kivcet furnace, while the zinc smelter processes the zinc-containing fume produced by the lead smelter [8] .A material circulation system is built within the plant to achieve closed loop of lead and zinc materials.This process has improved the comprehensive recovery efficiency of valuable metals, achieved maximum resource utilization and minimized emissions of "3 wastes", furthermore, met the clean production require of the time.The application of Kivcet process is of great significance for promoting the energy conservation and emission reduction career in China's lead-zinc industry.

JCC Kivcet Process
As shown in Figure 1, the Kivcet technique includes severe processes: mixing of metal-bearing materials and fluxes (charge preparation system), drying and ball-milling of charge, mixing of charge, coke and oxygen (feeding system), Kivcet flash smelting process, as well as slag fuming, dust collection and return, waste heat recovery, and continuous copper drossing.The Kivcet process has a wide adaptability to raw materials and can process various materials, such as lead concentrate, complex ore, complex lead-zinc materials, lead-containing residue, etc.

Charge preparation process
In order to achieve fine control of Kivcet charge, the smelter utilizes bin proportioning method together with computer software and manual supervisory to complete the charge preparation process.After preliminary screening, the charge is sent to the dry grinding process through a belt conveyor.As for dried and screened coke, part of it is fed into the reaction section burner by the belt weigher, forming a hot coke layer, while other coke is fed into the electrothermal section of the Kivcet furnace.

Drying and ball-milling process
After the charge preparation process, a φ3000×23000 mm steam dryer is used for charge drying to ensure that the moisture content of the charge is less than 1%.Before the dried charge is transported by positive-pressure pneumatic conveying system to the top silo or large storage bin of Kivcet furnace, it is ball-milled and screened to ensure that the granularity is about 1-2 mm.

Kivcet smelting process
The Kivcet equipment layout is shown in Figure 2, which is divided into two parts according to smelting function: the smelting section and the electrothermal section.The smelting section is mainly composed of reaction shaft, setting bath, uptake shaft, etc.The electrothermal section is mainly composed of furnace roof, side wall, setting bath and electrode system.The two setting baths are integrated.During operation, the smelting section is separated from the electrothermal section by means of a partition wall, made of water cooled copper elements, partially immersed into the slag bath.
Figure 2. The Kivcet equipment layout [9] Accurately measured furnace charge and oxygen are fed into the reaction shaft through four venturi charge burner to complete reactions such as smelting, oxidative desulfurization, decomposition, interaction and slagging.Due to its large size, coke falls faster, exothermic oxidation reaction occurs on coke's surface as it falls, then a "coke checker" floats on the surface of setting bath.The formation of coke layer is one of the essential technical features of the Kivcet process, where 80%-85% lead oxide is reduced in the coke layer, and the remaining lead oxide is reduced in the electrothermal section.The flue gas in the reaction shaft will be separated by the partition wall, and the melt will spontaneously floats to the electrothermal section under the effect of the potential energy difference between the liquid level.
In the electrothermal section, a variety of reactions can occur, including: the unreduced lead oxide in the slag is reduced again by coke, the gravitational separation of lead and dross, and the reduction volatilization of zinc oxide in the slag.The upper dross and lower bullion layered in the electrothermal section will be intermittently discharged from the slag taphole and bullion taphole.
Sulfurous gas generated from the reaction shaft goes into the shaft boiler to generate medium-pressure steam for electricity generation through heat recovering.The dedusted gas is directed to the sulfuric acid workshop for acid production, and the collected dust is returned to the reaction shaft of Kivcet furnace.
The zinc vapor generated by reduction process in the electric furnace needs to be re-oxidized into zinc oxide gas by blasted air.The zinc oxide gas will be transported to the zinc smelter after dust collection and purification.The cooled, cleansed gas can measure up the national emission standard, and is finally vented to atmosphere.

Continuous copper drossing process of bullion
The bullion at the bottom of the Kivcet furnace is discharged from the lead taphole by punching, the molten bullion is conducted to the continuous copper drossing furnace, where the bullion liquid circulates [10] .Sulfur is added to the furnace, so that the copper in the bullion will be converted into matte for copper removal.After this process, the copper content of bullion is generally less than 0.1%.Then the bullion is added to the smelting pot and pumped into the anode casting pot, so that large anode plate (each weigh about 370 kg) can be casted in vertical mold casting machine.The cooled anode plate is sent to the bullion electrolysis process through an automatic conveyor line.The anode residue generated from electrolysis is returned to the smelting pot through the automatic conveyor line for recasting.The 3D effect of the Kivcet furnace and the continuous copper drossing furnace is shown in Figure 3. Figure 3. 3D effect of the Kivcet furnace and the continuous copper drossing furnace [11] 2.5 Slag fuming process An 18m 2 slag fuming furnace is built to deplete the metal-rich slag generated from the Kivcet furnace, the slag is intermittently discharged into the slag fuming furnace through the chute for fuming.The essence of Kivcet slag fuming is reduction volatilization of valuble metals, where fine coal acts as reducing agent.The fine coal measured by an annular balance, is conveyed by primary air to the mixing burner to mix with the secondary air.The air pressure for fine coal transportation is generally 0.6-0.8MPa.The pressure of primary and secondary air, blown into the slag fuming furnace, is about 0.1 MPa, which can effectively disperse the fine coal, stir the slag melt inside the furnace, drive the reduction volatilization process of metal oxides.The high-temperature flue gas generated from fuming process in the slag fuming furnace is treated by heat recovery and purification.The secondary zinc oxide dust collected by the procedure above will be sent to the zinc smelter for treatment.The granulation slag of fuming furnace is sent to the stock yard for storage or sale through a belt conveyor.

Operation overview
The initial construction of JCC Kivcet furnace was completed in February 2012, then a trial operation was launched in March for practical production inspection of Kivcet technique.The furnace has been in operation for 11 years since 2012, only three shutdown maintenances were conducted in 2014, 2018 and 2021.Table 1 provides an overview of the previous shutdown maintenances.

Problems encountered in production
During years of operation practice, there are some equipment problems and process issues encountered, for example: (1) Leakage of the Kivcet boiler.One same boiler tube in the uptake shaft leaked several times, there might be problems in the installation process of the boiler.
(2) Large amount of furnace accretion.This is a disadvantage for melt discharge.
(3) The inefficiency of the coke layer.This leads to a higher lead content in the slag.
(4) Large amount of accretion in furnace and electrostatic precipitator.Therefore, the operation of the furnace had to be interrupted for cleaning.
(5) Excessive crack and consumption of electrode.

Technical optimization of Kivcet technique
In face of problems arising in production, the company has established a technical team to further study the process.They carried out a large number of experiments, and actively tried to find new solution, so that the production can accord with or superior to the designed standards.
(1) Mastering the control method of Kivcet process.This has significantly reduced the amount of accretion and improved the productivity of the furnace.The daily feeding amount has increased from 1164t (designed) to over 1250t (actual).
(2) The Kivcet furnace is designed to process slag generated from production of 100,000 t/a zinc, but the processing capacity of zinc slag in lead smelter can match 130,000 tons of zinc in 2022.The significant increase in slag processing capacity has led to a change in the Kivcet charge structure.In particular, the amount of lead in charge decreased from 30% (designed) to 20%.
(3) Improvement of the coke layer efficiency.This results in the lead content decrease to 2%-3%, lower than the planning value 4%.
(4) The prolongation of the Kivcet furnace production life, the corresponding maintenance cycle is also prolonged from the original 2 years to 4 years.
(5) Two 40mm diameter matte tapholes were installed on the side wall of the electric furnace to carry out the practice of directly producing matte (copper content aroud 40%) in the Kivcet furnace.

Conclusion
The decade's production practice of the Kivcet furnace amply proves that the Kivcet process has advantages such as high energy utilization rate, strong raw material adaptability, high zinc leaching slag treatment capacity, low operating cost and effective comprehensive recovery.
At present, the domestic and international processing charge of lead ore continue to hover low.In the future, we will further enhance our comprehensive recovery capacity, not only aims at increasing the production of matte in the Kivcet furnace, but also studying the advanced treatment process of matte to further recover metals such as lead, zinc, silver and indium.Moreover, we will try to find detailed solution for arsenic and selenium recovery and treatment.We believe that the feature of Kivcet technique -processing complex polymetallic raw materials is the vitality for lead-zinc smelting enterprises of the future.

Figure 1 .
Figure 1.General flow sheet of JCC Kivcet process

1 )
Replace chrome bricks on the side wall and roof of the electric furnace； 2)Replace lead tapping jacket； 3)Repair overlay of uptake shaft.

Table 1 .
Overview of the Kivcet shutdown maintenances