Cellhouse, zinc

In the electrolyte storage and mixing station, the neutral leach solution is mixed with spent electrolyte to adjust the composition of the electrolyte fed to the cellhouse. In the cellhouse, zinc is plated and then it is melted and cast into six-ton ingots. 

Asarco tested components of sulfur concrete, both precast and poured in place, in corrosive environments of sulfuric acid. Favorable endurance of these samples led to a full-scale cooperative demonstration project. The project selected was the rehabilitation of an electrolytic zinc cellhouse basement floor of approximately 21,000 square feet. 

The electrolytic plant plates zinc metal from the purified solution. The cellhouse contains four sections of cells, each with its own rectifier. Individual cells contain 50 cathodes and 51 anodes. Cathodes are mechanically stripped every 72 hours. Each section in the cellhouse contains its own double-masted crane for pulling cathodes, which are fed to any one of four stripping machines. 

The lijima Zinc Refinery is being challenged to become more profitable by recovering all by-products, such as Au, Ag, Cu, Pb, rare metals, iron oxide and so on. An increase in zinc production caused an increase in these metals as well. Simultaneously, the fixed cost decreased significantly with an expansion and cellhouse automation. We achieved one of the most competitive costs in the world. 

The zinc dust piuification circuit in the oxide leaching plant was originally conunissioned as a purification system for an old oxide cellhouse, decommissioned about 20 years ago when the oxide and calcine leaching plant electrolytes were combined. However, the oxide purification circuit continued to operate with about one gram per liter addition of dry zinc dust, principally to cement cadmium in the oxide electrolyte prior to entering the calcine leaching plant. A portion of the purification residue was then forwarded directly to the cadmium plant. Some arsenic was also removed fix>m solution. 

In reality, the system was very complex to operate with multiple addition points for reagents, zinc dust and spent cellhouse acid. The circuit included a set of cyclones to allow a portion of the solids to be recycled to maintain the solids density at rq>proximately 15 g/L in the tanks. To prevent excessive sanding-out in the purification tanks, e flow through the tanks was maintained by recycling, fiom the filters, a portion of the product filtrate. There were several problems with this circuit ... 

REVIEW OF ENGINEERING AND CONSTRUCTION FACTORS IN BUILDING A ZINC CELLHOUSE... 

The selection of the electrical equipment can play a major part in negotiating the price paid for electricity for the plant. The zinc cellhouse is a major consumer of electricity and may be the most important load on the distribution grid in the area. The characteristics of the rectifiers that affect the performance of the grid must be controlled much more closely than would be demanded of a minor consumer. 

Table IV - Fundamental Zinc Cellhouse Design Criteria that Impact on Building Cost...

Increasing the current density usually decreases the building size for a given zinc production. This assumes that the total cathode area is reduced, translating into fewer and/or smaller cells. Most modem cellhouses operate in the range of 400 - 500 A/m. However, current densities ranging from <300 A/m to >750 A/m are encountered. 

Reducing the electrode spacing decreases the building size for a given zinc production. The standard electrode spacing in modem compact cellhouse designs is 90 mm (center to center). Spacings as small as 80 mm have been reported. A 10 mm decrease represents an increase of approximately 12% in zinc production per cell, based on 125 cathodes per cell. 

A complete cellhouse project will take two to three years from the initiation of a feasibility study to the start of zinc production. The main activities in the project schedule will be ... 

The replacement cellhouse has the fallback position of using the old facility in the event of a construction delay. This will provide the necessary zinc production, but it does come at a... 

A. Caufriez, M. Dubois and E. Lejay, Zinc Cellhouse, Concept and Practice at Union Miniere , Zinc and Lead Processing. J. E. Dutrizac, J. A. Gonzalez, G. L. Bolton and P. Hancock, Eds., The Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, Canada, 1998,337-352. 

R. H. Honey, R. C. Kerby and R. C. Legge, Zinc Cellhouse Optimization , Zinc 85. K. Tozawa, Ed., Mining and Materials Processing Institute of Japan, Tokyo, Japan, 1995, 349-363. 

The tankhouse has been designed to reach a production of 137,000 tonnes of zinc cathode per year. The components have been designed for a potential maximum zinc cathode production of 190,000 t/y. The new D tankhouse is located next to the C cellhouse which was commissioned in May 1991. The space available is limited. The tankhouse footprint has been optimised at 0.02 m per tonne of cathode installed (design production). The supervision and housekeeping of the D and C tankhouses will be shared. This arrangement will reduce the manpower to 0.29, and preventive and predictive maintenance man-hours per tonne of zinc cathode produced to 0.09. 

Operation of the Kidd electrolytic zinc plant commenced in 1972 with a cellhouse capacity of 105,000 tonnes of zinc cathode. The original cellhouse layout consisted of 42 parallel rows for a total of 588 cells. As leaching capacity increased, the cellhouse was expanded to 630 cells. Zinc cathode was manually stripped from plant start-up until the development of a mobile automated stripping system in 1994. Machine development continued until a second unit was placed in production in 1996, from which point, 60 % of the cellhouse was being stripped with the automated system. The final phase of the project was implemented in 1999 with the commissioning of two more automated strippers. This paper describes the implementation of the automated stripping system and its impact on cellhouse productivity. 

Figure 7 depicts the productivity gains achieved since the project s inception in 1993. It should be noted that the 1998 zinc production is the highest on record with 151,000 tonnes stripped for the year. This was achieved with 60% of the cellhouse output stripped by two automated stripping machines. 

F. Tamargo and Y. Lefevre, Concept and Operation of the New Conventional Cellhouse of Austuriana de Zinc at San Juan de Nieva, Spain , World Zinc 93. I.G. Matthew, Ed., Australasian Institute of Mining and Metallurgy, Parkville, Australia, 1993,295-306. 

Eventually, as the anodic process continues, a hard, dense, protective layer of Pb02 is formed on the anode surface. Once this protective film has been formed, cathode contamination decreases and the amount of sludge generated by the anode decreases as well. This process (called conditioning) may take 30-60 days or more depending on the anode composition and current density (1). Because of the difficulty in conditioning anodes, operators of zinc cellhouses are very reluctant to replace an entire cell of used, conditioned anodes with new, unconditioned anodes. Operators will normally replace only one or two anodes per cell or try to condition the anodes prior to use in the cells. 

Zinc EW was the first large-scale EW process to develop surface tension affecting foams and cross flow cellhouse ventilation designs, that were eventually used in copper ... 

Crossflow ventilation is a technology that has been designed into the cellhouse structure in the past to reduce acid mist. Amplats Rustenberg plant in South Africa applied a cross flow principle first and this was applied on a larger scale at the zinc EW cellhouses in Canada (Cominco Trail in early 1980 s) and Kidd Creek. From the mid 1990 s until the more commonplace application of cell hoods, the large tankhouses in Chile typically used combinations of positive crossflow ventilation, balls and foams. The DESOM crossflow ventilation configuration, which became common practice in Chile, was first applied to the El Teniente SX-EW operation in 1985. Cerro Colorado, Quebrada Blanca, Chuqui SBL, Quebrada M and Escondida Coloso followed in 1994. 

In most base metal cellhouse operations around the world, a combination of the previously discussed technologies is implemented [4, 16]. Most copper EW plants around the world operate with a surfactant and mist suppression balls on top of the electrolyte. This can be combined with cell hoods or cross flow ventilation. Some zinc EW plants have combined cross flow ventilation systems in the cellhouse, with the use of surfactants in the cells, but typically most zinc plants use surfactants only [2]. Cawse Nickel combined anode bags with cross flow ventilation, as shown in Figure 6 [10]. The nickel industry is now also using cell hoods [5],... 

Modem cellhouse design aims to minimize operator and environmental exposure to cellhouse acid mist. The transfer of EW cellhouse technologies between zinc, copper, and nickel has led to improvements in acid mist capture technology. These technologies include electrode bags and skirts, more efficient cell ventilation and improved surfactants. 

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