Zinc Recycling

Recycling Zinc in Viscose Rayon Plants by Two-Stage Precipitation... 

Zinc is a bluish-white, lustrous metal which tarnishes in air. It is present in the earth s crust as sulfide (sphalerite), carbonate, or silicate ores, to the extent of only 78 ppm, making it the 23rd most abundant element.2 The metal is obtained from its ores by roasting and subsequent reduction with coke or by electrolysis. Approximately 8.36 million metric tons of zinc were produced worldwide in 2002 of this amount, two-thirds were from ores, while one-third was obtained from recycled zinc.3 The ease of mining and refining of the ore and the subsequent low price of the metal (ca. 1.2 kg-1 in 1998)3 have made zinc the third most popular non-ferrous metal (after aluminum and copper). 

Lead-acid batteries received a high score by virtue of being a commercial product with an established recycling infrastructure. Nickel/metal hydride and nickel/cadmium are also widely available commercially and are routinely recycled. Zinc batteries are sold in large quantities and little or no hazardous waste and pollutants are produced by processing. Most of the battery technologies farther down the list are ranked lower because the batteries are not commercial products and recycling processes are not developed any further than a bench scale. In the case of sodium/sulflir batteries, the market outlook for recovered products is unfavorable. 

Some 80% of the zinc available for recycling is currently recycled. Indeed, 30% of the world s zinc supply (2.9 million metric tonnes) is derived from recycled zinc. 

Chem. Descrip. French process zinc oxide from recycled zinc metal... 

Chem. Descrip. French process zinc oxide from recycled zinc metal CAS 1314-13-2 EINECS/ELINCS 215-222-5 Uses Pigment, filler for ceramics, paints... 

Two publications on zinc recycling Zinc Recycling - The General Picture and Zinc Recycling - Zinc Coating Steel have been published by IZA-Europe, in co-operation with EGGA and EUROFER. 

G. Houlachi, A. Condy and R.W. Stanley, Review of Zinc Recycling , Zinc Lead 95. T. Az ami, N. Masuko, J.E. Dutrizac and E. Ozberk, Eds., The Mining Materials Processing Institute of Japan, Tokyo, Japan, 1995,417-431. 

Zinc concentrate (60 wt.% Zn) is obtained by common froth flotation from run-of-mine sulfidic ores usually containing from 4 to 8 wt.% Zn. Nevertheless, it is important to note that, despite the fact that most of the concentrates used are of sulfidic origin, some oxide concentrates are sometimes also used along with recycled zinc oxide from the pyrometallur-gical pretreatment of steel, e.g., Waelz oxide. Usually, the main mineral species is zinkblende... 

Liquid Effluents. Recycling of acid, soda, and zinc have long been necessary economically, and the acid—soda reaction product, sodium sulfate, is extracted and sold into other sectors of the chemical industry. Acid recovery usually involves the degassing, filtering, and evaporative concentration of the spent acid leaving the spinning machines. Excess sodium sulfate is removed by crystallization and then dehydrated before sale. Traces of zinc that escape recovery are removable from the main Hquid effluent stream to the extent that practically all the zinc can now be retained in the process. 

Lead [7439-92-17, Pb, is an essential commodity ia the modem iadusttial world, ranking fifth ia tonnage consumed after iron (qv), copper (qv), aluminum (see Aluminumand aluminum alloys), and 2iac (see Zinc and zinc alloys). In 1993, the United States accounted for 30% of the 4,450,000 metric tons of refined lead consumed by the Western world. Slightly over half of the lead produced ia the world now comes from recycled sources (see Recycling, NONFERROUS LffiTALS). 

Whereas many of these technologies are not really new, they have never had the regulatory and economic justification for their use in metallizing. Each of these general methods has many variants. Some may be directed to waste treatment, some to recycle, and some to reclaim. An example is filtration, used to prevent release to air of zinc particles from flame spraying, microfiltration of cleaners to extend hfe, in combination with chemical precipitation to remove metal particles from wastewater, and many other uses. 

Henkel Rearrangement of Benzoic Acid and Phthalic Anhydride. Henkel technology is based on the conversion of benzenecarboxyhc acids to their potassium salts. The salts are rearranged in the presence of carbon dioxide and a catalyst such as cadmium or zinc oxide to form dipotassium terephthalate, which is converted to terephthahc acid (59—61). Henkel technology is obsolete and is no longer practiced, but it was once commercialized by Teijin Hercules Chemical Co. and Kawasaki Kasei Chemicals Ltd. Both processes foUowed a route starting with oxidation of napthalene to phthahc anhydride. In the Teijin process, the phthaHc anhydride was converted sequentially to monopotassium and then dipotassium o-phthalate by aqueous recycle of monopotassium and dipotassium terephthalate (62). The dipotassium o-phthalate was recovered and isomerized in carbon dioxide at a pressure of 1000—5000 kPa ( 10 50 atm) and at 350—450°C. The product dipotassium terephthalate was dissolved in water and recycled as noted above. Production of monopotassium o-phthalate released terephthahc acid, which was filtered, dried, and stored (63,64). 

P. B. Queneau, B. J. Hansen, and D. E. SpiUer, in "Recycling Lead and Zinc in the United States," Proceedings of the Milton E. Wadsworth 4th International Symposium on liydrometallurgy, AIME SME/TMS, Salt Lake City, Utah, Aug. 1—5,1993. 

Residual traces of zinc are released during vacuum sintering of cemented carbides made with recovered powders. This can be troublesome when a buildup of zinc occurs in the furnace. Teledyne Advanced Materials further developed this process on a commercial basis by achieving zinc levels in the low ppm range (<30 ppm). The fact that the materials were vacuum-sintered in their original form where certain impurities are removed leads to lower impurity levels in the recovered powders. There is a slight oxidation or loss of carbon that must be compensated, otherwise the recycled powder is not in any way inferior to the original. 

Human toxicity, aquatic toxicity, and the environmental impact of engine coolants and deicing fluids ate typically measured on the fresh fluid only. Spent fluids contain varied contaminants that can drastically affect the toxicity and environmental impact of the fluid. Most pronounced is the impact of heavy-metal contaminants in spent antifreeze. Data on spent and recycled antifreeze, compiled by the ASTM Committee on Engine Coolants, show an average lead level 11 ppm, as weU as various other metal contaminants (iron, copper, zinc) (18). The presence of these contaminants in a used fluid may require special disposal techniques for the fluids. 

---