Metallic lead

Elements with high atomic weights are especially suitable as absorbers for X-rays and gamma radiation. For that reason, lead has an important use as protection against radiation in laboratories and hospitals in which X-ray methods are utilized, and lead protection is used in the nuclear industry. Lead foils are used, for similar reasons, for packing of radioactive preparations and X-ray films. 

Electrical cables were earher sheathed mainly with lead. Nowadays sheathing is made with plastic, at least for cables above ground. For subterranean and submarine cables, the demand for good corrosion resistance has however made lead necessary. This lead is often alloyed with about 1% antimony. 

The noise-absorbing ability of lead has been observed by architects. Thin lead foils in interior hotel walls and in office walls make small wall thickness possible, with corresponding increase of the floor space. Lead has also been tested as a shock absorber for buildings in earthquake regions. 

Molten lead has a very good heat transfer abihty and is used in the continuous heat treatment process for the manufacture of high-carbon steel wire. This process demands a very rapid heating from room temperature to 450°C (temjjering after hardening) and a very quick cooling from 900°C to 550°C (so-called lead patenting). The lat- 

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Leaded brass Leaded bronzes Leaded Muntz metal Leaded red brass... 

Flotation or froth flotation is a physicochemical property-based separation process. It is widely utilised in the area of mineral processing also known as ore dressing and mineral beneftciation for mineral concentration. In addition to the mining and metallurgical industries, flotation also finds appHcations in sewage treatment, water purification, bitumen recovery from tar sands, and coal desulfurization. Nearly one biUion tons of ore are treated by this process aimuaHy in the world. Phosphate rock, precious metals, lead, zinc, copper, molybdenum, and tin-containing ores as well as coal are treated routinely by this process some flotation plants treat 200,000 tons of ore per day (see Mineral recovery and processing). Various aspects of flotation theory and practice have been treated in books and reviews (1 9). 

Process. The QSL process (14) is a continuous single-step process having great flexibiUty in regard to the composition of the raw materials. In this process the highly exothermic complete oxidation, ie, the roasting reaction, can be avoided to some extent in favor of a weakly exothermic partial oxidation directly producing metallic lead. However, the yield of lead as metal is incomplete due to partial oxidation of lead to lead oxide. 

The remaining lead must be oxidized and later can be reduced from the slag using carbon. The ratio of metallic lead to lead oxide which depends in part on the type of raw materials to be processed, can be adjusted within certain limits by varying the degree of oxidation. In treating lead-rich concentrates having a lead content of approximately 70%, more than 75% of the lead can be obtained directly as metallic lead. 

Some of this material is reclaimed by ketde melting and refining. However, most scrap is a combination of metallic lead and its aUoying constituents mixed with compounds of these metals, usuaUy oxides and sulfates. Therefore, recovery as metals requires reduction and refining procedures. 

A typical automobile battery weighs 16.4 kg and consists of 3.5 kg metallic lead, 2.6 kg lead oxides, 4.0 kg lead sulfate, 1.3 kg polypropylene, 1.1 kg PVC, mbber and other separators, and 3.9 kg electrolyte. Including acid and water, the lead-beating parts represent 61 wt %, ie, 21 wt % of lead alloy (2% Sb) and 40 wt % lead oxides and sulfate. Nonlead-beating parts constitute the remaining 39% the case (hard mbber or polypropylene) and separators (PVC) at 15 wt % and the electrolyte at 24 wt %. 

Lead Monoxide. Lead monoxide (litharge), PbO, occurs as a reddish alpha form, which is stable up to 489°C where it transforms to a yellow beta form (massicot). The latter is stable at high temperatures. The solubihty of a-PbO ia water is 0.0504 g/L at 25°C the solubihty of the p-PbO is 0.1065 g/L at 25°C (40). Lead monoxide is amphoteric and dissolves ia both acids and alkahes. In alkahes, it forms the plumbite ion PbO - The monoxide is produced commercially by the reaction of molten lead with air or oxygen ia a furnace. Black or gray oxide is manufactured by the Barton process, by the oxidation of atomized molten lead ia air, as well as by the ball mill process, ia which metallic lead balls of high purity are tumbled ia the mill to form partially oxidized lead particles. 

Lead nitrate [10099-74-8] Pb(N02)2, mol wt 331.23, sp gr 4.53, forms cubic or monoclinic colorless crystals. Above 205°C, oxygen and nitrogen dioxide are driven off, and basic lead nitrates are formed. Above 470°C, lead nitrate is decomposed to lead monoxide and Pb O. Lead nitrate is highly soluble in water (56.5 g/100 mL at 20°C 127 g/100 mL at 100°C), soluble in alkalies and ammonia, and fairly soluble in alcohol (8.77 g/100 mL of 43% aqueous ethanol at 22°C). Lead nitrate is readily obtained by dissolving metallic lead, lead monoxide, or lead carbonate in dilute nitric acid. Excess acid prevents the formation of basic nitrates, and the desired lead nitrate can be crystallized by evaporation. 

Two processes, developed for the direct processing of lead sulfide concentrates to metallic lead (qv), have reached commercial scale. The Kivcet process combines flash smelting features and carbon reduction. The QSL process is a bath-smelting reactor having an oxidation 2one and a reduction 2one. Both processes use industrial oxygen. The chemistry can be shown as follows ... 

ISlew Synthetic Approaches. There have been a number of efforts to prepare quinolines by routes quite different from the traditional methods. In one, the cyclization of 3-ariiino-3-phenyl-2-alkerLiniines (18) using alkah metals leads to modest yields of various 4-arylaminoqurnolines (54). Because this stmcture is found in many natural products and few syntheses of it exist, the method merits further investigation. 

Fig. 1. Recycling of the nonferrous metals ( ) lead, ( ) nickel (stainless steel), (U) copper, (S) aluminum, and ( ) 2iac from secondary sources from 1989...

Corrosion Control. Sihca in water exposed to various metals leads to the formation of a surface less susceptible to corrosion. A likely explanation is the formation of metahosihcate complexes at the metal—water interface after an initial dismption of the metal oxide layer and formation of an active site. This modified surface is expected to be more resistant to subsequent corrosive action via lowered surface activity or reduced diffusion. 

After curing, the plates are allowed to finish the drying process in ambient or elevated temperature air. The moisture and metallic lead content of the cured plates should be substantially reduced to less than 2%. 

Product specifications for microbial food enzymes have been estabUshed by JECEA and ECC. They limit or prescribe the absence of certain ubiquitous contaminants such as arsenic, heavy metals, lead, coliforms, E. coli and Salmonella. Furthermore, they prescribe the absence of antibacterial activity and, for fungal enzymes only, mycotoxins. 

Toxic heavy metals and ions, eg, Pb, Hg, Bi, Sn, Zn, Cd, Cu, and Fe, may form alloys with catalytic metals (24). Materials such as metallic lead, ziac, and arsenic react irreversibly with precious metals and make the surface unavailable for catalytic reactions. Poisoning by heavy metals ordinarily destroys the activity of a precious-metal catalyst (8). 

Air-poUutant effects on neural and sensory functions in humans vary widely. Odorous pollutants cause only minor annoyance yet, if persistent, they can lead to irritation, emotional upset, anorexia, and mental depression. Carbon monoxide can cause death secondary to the depression of the respiratory centers of the central nervous system. Short of death, repeated and prolonged exposure to carbon monoxide can alter sensory protection, temporal perception, and higher mental functions. Lipid-soluble aerosols can enter the body and be absorbed in the lipids of the central nervous system. Once there, their effects may persist long after the initial contact has been removed. Examples of agents of long-term chronic effects are organic phosphate pesticides and aerosols carrying the metals lead, mercury, and cadmium. 

Fig. 19-4 Older anode system for roadway plates (a) Silicon iron anodes in coke breeze bed, (b) noble metal lead in conducting bedding in a trench.

Metal Lead Calcium Sodium Potassium Vanadium... 

Threshold determinations for metal-containing compounds present a special case. If, for example, you process several different lead compounds, you would base your threshold determination on the total weight of all lead compounds processed. However, If you process both the parent" metal (lead) as well as one or more lead compounds, you must make threshold determinations for both because they are separately listed toxic chemicals. If you exceed thresholds for both the parent metal and compounds of that same metal, EPA allows you to file one combined report (e.g., one report for lead compounds, including lead) because the release Information you will report In connection with metal compounds will be the total pounds of the parent metal released. 

A lead-acid battery consists of electrolytic cells, each containing an anode of porous lead, a cathode of primarily lead peroxide (PbO,), and electrodes of metallic lead. The anode and cathode are separated by nonsulfuric acid and water. 

The cast grids are made into battery anode and cathode plates by the application of a lead oxide paste of 70 percent lead oxide (PbO) and 30 percent metallic lead. Lead ingots are tumbled in a ball mill with airproducing lead oxide and fine lead dust (referred to as leady oxide ). Leady oxide particulates are entrained in the mill exhaust air, which is treated sequentially by a cyclone separator and fabric filter. The used fabric filter bags are shipped to a RCRA-permitled commercially operated ha2ardous waste landfill located in Colorado. The leady oxide production process does not produce wastewater. 

The plates are dried and cured under controlled temperature and humidity conditions producing no wastewater or particulate emissions. Cured plates are sent to a three-process operation that involves manual separation of the plates, stacking them with non-conducting separators, and the welding on of metallic lead battery leads (pronounced leeds ) and lead terminals. The plates are then assembled Into battery cases. 

Sulfuric acid is added to the assembled batteries and the plates are formed within the batteries by applying electric voltage. The formation process oxidizes the lead oxide in the positive plates to lead peroxide and reduces the lead oxide in the negative plates to metallic lead. The charging process produces an acid mist that contains small amounts of lead particulate, which is released without emission controls. 

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