Big River Zinc

The apparent United States consumption of cadmium in 1988 was estimated to be 3620 t. Of the 2482 t imported, over 85% came from Canada, Mexico, Germany, and AustraUa. The principal domestic producers and suppHers of cadmium metal are ASARCO, Inc. Big River Zinc Corp. Jersey Miniure Zinc Co. and Zinc Corp. of America. 

Big River Zinc Corporation, 201, 220 Bihar Caustic Chemicals Ltd., 170 Bilbaina de Alquitranes, 202 Billiton Pic, See BHP Billiton Pic (UK), 207 BIMOL Research Laboratories Inc., 220 Biochemie GmbH, 143 BIODAC , ethylene oxide, 25 Biphenyl, 25... 

In the USA, BIG RIVER ZINC developed a process designed to produce cadmium oxide directly from pocket-plate negative electrodes. It discontinued this process when the price of cadmium fell very sharply in 1991/1992. 

BRZ Big River Zinc Corp., personal communication James, Steve March 23, 1999... 

Big River Zinc Corporation 2401 Mississippi Avenue Sauget, Illinois, U.S.A. 62201... 

IMPROVEMENTS AT THE ELECTROLYTIC ZINC PLANT OF BIG RIVER ZINC CORPORATION, SAUGET, ILLINOIS, U.S.A. 

Significant modifications to the electrolytic zinc plant operated by Big River Zinc Corporation were made at the end of the 1990 s resulting in increased oqtacity and improved efficiencies. A new cell room, with the innovative use of acid-resistant concrete cells and a modem ventilation system, was installed to raise the capacity fiom 80,000 tonne/y to 106,000 tonne/y of finished zinc. Improvements to the leaching section include the conversion from a single to a two-step process, with associated equipment changes, to improve the quality of the residues produced. Another key change is the constmction of a facility to allow the use of zinc oxides fk>m secondary sources as a feed to the plant. This paper describes these improvements and the current operations. 

In April 1996, Korea Zinc acquired the zinc assets of Big River Minerals but retained the name of its new US subsidiary as the Big River Zinc Corporation. Korea Zinc saw in the Sauget refinery an opportunity for growth for the following reasons ... 

Figure 1 - The Revised Sulfuric Acid Plant for Big River Zinc...

Figure 7 - Trend for Big River Zinc Cathode Production...

Table I - Chemical Composition of Big River Zinc Calcine and Ameristeel Crude Zinc Oxide...

The overall criteria were to install a facility that would allow Big River Zinc to process crude zinc oxide through its electolytic zinc plant. The limitations for processing crude zinc oxides have been described previously (3). TTie relatively high levels of chloride and fluoride pose significant problems. 

Big River Zinc investigated two processes to dechlorinate the oxides. The first process used a water wash accompanied with a pH adjustment to minimize zinc losses. Htis method offered a known technology because Big River Zinc provided assistance to ZTT in Caldwell, Texas, to refine their similar process. Tests showed that washing, followed by neutralization with soda ash, succeeded in reducing the chloride content to less than 1% in the final product. The other process investigated was thermal dechlorination (4). It is known that thermal dechlorination can remove over 90% of the chlorides fiom roaster feeds. A few tests indicated promising results for this technique but the decision was taken to pursue washing as the process of choice. 

The first step in the plant design was to acquire all the necessary permits relevant not only to the construction of e plant but also for the classification of the material. Big River Zinc worked with the various government agencies to remove the hazardous waste stigma from the erode zinc oxide derived from the EAF dusts. The efforts paid off in May 1999, when Big River Zinc received an Adjusted Standard from the Illinois Pollution Control Board declaring that zinc oxide derived from EAF dust is a product, and not a derived hazardous waste, when recycled at the BRZ zinc refinery. 

Figure 1- Flowsheet of the Big River Zinc Oxide Washing Plant...

The integration of the washing plant into the Big River Zinc process revolves around the following factors ... 

The plant design allows for the future construction of a conveyor to carry the washed oxide directly to the concentrate storage shed. At present, the washed oxide falls into a dump truck that the operator empties once or twice a shift. Big River Zinc decided to delay the installation of a conveyor until the process has been proven and the plant production reached a higher level. We are also evaluating possible means of adding the washed oxide directly to the leach circuit. 

The capacity for imdesirable elements at Big River Zinc falls into two categories. The first category involves elements such as sodium and potassium. These elements do not affect the equipment and they do not directly affect the process. The problem with these elements is that the process used at Big River Zinc does not eliminate them. As a result, they build up in the electrolyte resulting in a lower zinc solubility. This increases the production cost because of the need to treat more solution to produce the same quantity of zinc. 

The other category of impurities includes elements that are detrimental to the process or equipment. This category includes iron, lead, chloride and fluoride. Iron is required in the process as a purification agent. However, it also generates residue that cannot be treated on site. Iron exits the Big River Zinc plant in the lead-silver concentrate. If the iron content is too high, the value of the concentrate is reduced, resulting in a cash flow reduction. Lead, as stated earlier, will cause problems in the roasters if its concoitration is too high. In the case of chloride and fluoride, their major impact is equipment corrosion. As with sodium and potassium, the leach and purification circuit does not eliminate chloride and fluoride. When the chloride or fluoride contents increase, we observe increased corrosion rates in the equipment, especially in the cellroom aluminum cathodes. 

Figure 2 - Chloride Balance in Big River Zinc s Solution Circuit Assiuning 200 mg/L of...

Fluoride is much harder to quantify in the system because of its low level. Big River Zinc is very sensitive to the fluoride concentration in the electrolyte. Because we do not condition the surface of the cellroom cathodes, we are limited to 10 mg/1 in the cell electrolyte. If we were able to brush the cathodes after stripping, we could tolerate up to 50 mg/1 of fluoride. 

Big River Zinc has demonstrated that it can help close the recycling loop for zinc and provide a service to the steel industry by effectively recycling crude zinc oxide recovered from EAF dust, basic oxygen furnace (BOF) dust and other sources of crude zinc oxide. Preventing large quantities of zinc-rich material from reaching landfills is an important first step. 

The construction of a washing plant at Big River Zinc represents a major step in the recycling of crude zinc oxide. The plant, originally designed to handle only oxide arriving in pneumatic trucks, was expanded to receive material in delivered pneumatic railcars. The next step will include the ability to handle material in supersacks. Big River Zinc s entry into the crude zinc oxide market now provides the North American steel industry with an additional viable market for recycling crude zinc oxide. 

Big River Zinc will continue to expand its crude zinc oxide washing facility to accommodate different sources of crude zinc oxide, and thereby, further increase its critical role in zinc industry stewardship. 

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