Mexico, lead production

In addition to domestic production of Frasch and recovered elemental sulfur, U.S. requirements for sulfur are met with by-product sulfuric acid from copper, lead, molybdenum, and zinc smelting operations as well as imports from Canada and Mexico. By-product sulfur is also recovered as sulfur dioxide and hydrogen sulfide (see Sulfurremoval and recovery). 

Mexican urethane demand has been constrained by raw materials costs. Flexible foam markets will show some strength in the 80 s, reflecting a steady auto production and moderate increases for furniture and bedding uses. Rigid foam applications are still in the early stages of market development but, commercial/industrial insulation uses are increasing well. Mexico leads Latin America in urethane elastomer usage, paced by its demand for shoe sole applications. 

II. Natural and Anthropogenic Sources of Lead in Mexico A. Lead Production... 

Mexico and Peru are the most important Latin American producers of lead (CRM 1988). From 1972 to 1976, lead production in Mexico was equivalent to 40% of the total world processed lead (Molina et al. 1979). In 1978, the production of refined lead reached a high of 225,472 metric tons and in recent years, production has kept a level of more than 180,000 metric tons per year (Fig. 2). From 1983 to 1987, Mexico was the sixth world producer of the metal there are no official data available for 1988 (CRM 1988). Lead production in the major producing countries is presented in Table 2 (WBMS 1989). 

From 50 to 60% of the Mexican lead production is used as oxides which enter into several industrial processes, in particular, battery manufacturing and production of tetraethyl lead. The remainder is used in the production of solder, cables, ammunition, pigments, paints, ceramics, enamels, and other products (Cortinas 1988). Another important use of lead in Mexico is in the manufacturing of metal parts that require lead alloys (Molina 1977) some relevant data are presented in Table 3 (IMZPC 1986, 1987). 

Table 5. Trends in tetraethyl lead production in Mexico ...

In Mexico, ores are available containing pyragyrite and proustite, mined entirely for silver extraction, and Mexico derives 50% of its silver production from mines containing these so-called primary silver minerals The other half is, as in the rest of the world, a by-product of copper, zinc and lead production. 

The most important ores are bismuthinite or bismuth glance and bismite. Peru, Japan, Mexico, Bolivia, and Canada are major bismuth producers. Much of the bismuth produced in the U.S. is obtained as a by-product in refining lead, copper, tin, silver, and gold ores. 

Mexico, the world s leading producer of silver since the Spanish conquest, obtains virtually its entire silver production from lead—2inc mines in the central cordillera. Mexico retained its dominance in silver production until the discovery of the Comstock Lode in Nevada in 1859. Discoveries in Colorado, Ari2ona, and Montana placed the United States as the world s top silver producer from 1871 until 1900. As these mines played out, Mexico s vast resources returned it to its former position of dominance. 

U.S. silver production from 1985 to 1994 averaged 1588 t/yr. Less than one quarter of this output comes from silver mine districts, however. About half is as by-product of gold mines about one quarter comes from copper and lead—2inc mines. The silver production in Mexico from 1985 to 1994 averaged 2256 t/yr, and Pern, at the southern extremity of the cordillera, where silver is a by-product of copper and lead—2inc mines, averaged 1810 t/yr. 

Bismuth is mined primarily as a by-product of the processing of ores of other metals, mosdy copper and lead. The countries that mine significant quantities of bismuth are AustraUa, BoHvia, Canada, China, Japan, Mexico, Pern, and the United States. Production is summarized in Table 3. 

Pineda-Zavela, A.P. et al., Nitric oxide and superoxide anion production in monocytes from children exposed to arsenic and lead in region Lagunera, Mexico, Toxicol. Appl. Pharmacol. 198, 283, 2004. 

Arsenic occurs primarily in sulphide minerals associated with copper ores, and to a lesser extent with zinc, lead and gold ores. Arsenic is produced as a by-product of the smelting of these metals. Primary arsenic production has now ceased in the USA and Europe, and most arsenic is now imported from China and Mexico. The volatility of arsenic represents a significant concern, and there is at present no known natural mechanism by which arsenic is immobilized in the environment. Anthropogenic activities account for an input of some 19000 tonnes into the atmosphere, compared with 12000 tonnes from natural processes, such as volcanism and forest fires (Ayres and Ayres, 1996). 

Ticks, arachnids of the order Acarina, are bloodsucking parasites which are of major economic importance in cattle production. Infestation by ticks leads to losses in meat and milk production, reduction in hide quality and exposure of the host to any diseases for which the tick is a vector. Moreover, the resulting skin lesions are sites for infestation by other parasites and infection. Control of ticks of the Boophilus species is of major importance in view of their widespread distribution (Australia, South Africa, South America, Mexico and Southern North America). This task has been made more challenging by the emergence of strains resistant to one or more of the classes of compounds described below. 

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