Oxidation lead sulfate

PIa.tes, Plates are the part of the cell that ultimately become the battery electrodes. The plates consist of an electrically conductive grid pasted with a lead oxide—lead sulfate paste which is the precursor to the electrode active materials which participate in the electrochemical charge—discharge reactions. 

Conventional pastes for use in making automotive batteries contain lead oxide in the range of 15-30%, sulfuric acid, water and additives such as fiber and expanders. Such pastes are usually made by adding the sulfuric acid and water to a mixture of lead and lead oxides. As a result of the chemical reaction during mixing, a portion of the lead and PbO is initially converted to lead sulfate (PbS04) and the resultant positive paste becomes a heterogeneous mixture of lead, lead oxide, lead sulfate and basic lead sulfates. 

Acid Oxidation. Reactions of lead with acid and alkaUes are varied. Nitric acid, the best solvent for lead, forms lead nitrate acetic acid forms soluble lead acetate in the presence of oxygen sulfuric acid forms insoluble lead sulfate. Sulfuric acid is stored in containers with chemical or acid-grade lead. Lead dissolves slowly in HCl, but in the presence of aqueous alkaUes forms soluble plumbites and plumbates. 

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 %. 

After acid removal, scrap batteries are fed to a hammer mill in which they are ground to <5 cm particles. The ground components are fed to a conveyor and passed by a magnet to remove undesirable contamination. The lead scrap is then classified on a wet screen through which fine particles of lead sulfate and lead oxide pass, and the large oversize soHd particles are passed on to a hydrodynamic separator. The fine particles are settled to a thick slurry and the clarified washwater recirculated to the wet screen. 

Reverberator Furnace. Using a reverberatory furnace, a fine particle feed can be used, the antimony content can be controlled, and batch operations can be carried out when the supply of scrap material is limited. However, the antimony-rich slags formed must be reduced in a blast furnace to recover the contained antimony and lead. For treating battery scrap, the reverberatory furnace serves as a large melting faciUty where the metallic components are hquefted and the oxides and sulfate in the filler material are concurrently reduced to lead metal and the antimony is oxidized. The furnace products are antimony-rich (5 to 9%) slag and low antimony (less than 1%) lead. 

PbO PbO H2O, for example, may be formed by boiling suspensions of lead oxide and lead sulfate in water. In addition, complex mixed salts, such as white lead, 2PbC02 Pb(OH)2, are readily formed. 

Tetrabasic Lead Sulfate. Tetrabasic lead sulfate [12065-90-6] 4PbO PbSO, mol wt 1196.12, sp gr 8.15, is made by fusion of stoichiometric quantities of Htharge (PbO) and lead sulfate (PbSO heat of formation, Ai/ = — 1814 kJ/mol (—434.1 kcal/mol). Alternatively, tetrabasic lead sulfate may be prepared by boiling the components in aqueous suspensions. At about 70°C, tribasic hydrate reacts with lead oxide to form tetrabasic sulfate. At 80°C, this transformation is complete in - 20 hours. Tetrabasic lead sulfate is used in limited quantities in Europe as a PVC stabilizer. However, in the United States, lead-acid batteries have been developed by BeU Telephone Laboratories, which contain tetrabasic lead sulfate. Such batteries are used for emergency power at telephone switchboard stations and have an anticipated service life of over 50 years. 

The most common white pigments are titanium dioxide, 2inc oxide, leaded 2inc oxide, 2inc sulfide [1314-98-3], and Hthopone, a mixture of 2inc sulfide and barium sulfate [7727-43-7]. The use of lead whites and antimony oxides has been decreasing steadily for environmental reasons. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Leaded Zinc Oxide. Oxides containing more than 5 wt % basic lead sulfate are classified as leaded and are made ia the American process from high lead materials, usually lead sulfide mineral, or by blending ziac oxide and basic lead sulfate. There is only one manufacturer ia the United States and the product contains 20—28 wt % basic lead sulfate. Leaded oxides are used only ia mbber ia the United States. 

Paste Mixing. The active materials for both positive and negative plates are made from the identical base materials. Lead oxide, fibers, water, and a dilute solution of sulfuric acid are combined in an agitated batch mixer or reactor to form a pastelike mixture of lead sulfates, the normal, tribasic, and tetrabasic sulfates, plus PbO, water, and free lead. The positive and negative pastes differ only in additives to the base mixture. Organic expanders, barium sulfate [7727-43-7] BaSO carbon, and occasionally mineral oil are added to the negative paste. Red lead [1314-41 -6] or minium, Pb O, is sometimes added to the positive mix. The paste for both electrodes is characterized by cube weight or density, penetration, and raw plate density. 

Lead Chromates and Molybdates. The lead chromates appear in several shades of yellow. The primrose and lemon are solid solutions of lead sulfate in the chromate and have the stable monoclinic stmcture. The medium shade contains no sulfate. Chrome orange is a compound with lead oxide (PbCrO TbO). Molybdate orange is a combination of lead chromate and sulfate with molybdate (PbMoO ). These pigments have the advantages of... 

Lead compounds were not found on the surrounding activated coating layer, rather only associated with the precious metal. The Pt sites are less poisoned by lead than are Pd or Rh sites because the Pt sites are protected by the sulfur in the fuel. Fuel sulfur is converted to SO2 in the combustion process, and Pt easily oxidizes SO2 to SO on the catalyst site. The SO reacts with the lead compounds to form PbSO, which then moves off the catalyst site so that lead sulfate is not a severe catalyst poison. Neither Pd nor Rh is as active for the SO2 to SO reaction, and therefore do not enjoy the same protection as Pt. 

Most black pigments are made of carbon black formed by depositing carbon from a smoky flame of natural gas on a metal surface. Lampblack is made similarly by burning oik Bone blacks are made from charred bones. Graphite occurs naturally or can be prepared from coal in electric furnaces. Mineral blacks come from shale, peat, and coal dust. Iron oxide blacks are found in nature or prepared. Blue lead sulfate is a pigment for priming. Of these, carbon black is su[XTinr. 

The older process is called the lead chamber process. It uses a mixture of gaseous oxides of nitrogen—nitric oxide, NO, and nitrogen dioxide, N02—as the catalyst. This process has been in use and under development for over 200 years. It is named after the large room-like chambers lined with lead in which the gaseous reactions are carried out. The lead walls react with the acid and become coated with an inert protective coating of lead sulfate. 

Lead oxide (PbO) (also called litharge) is formed when the lead surface is exposed to oxygen. Furthermore, it is important as a primary product in the manufacturing process of the active material for the positive and negative electrodes. It is not stable in acidic solution but it is formed as an intermediate layer between lead and lead dioxide at the surface of the corroding grid in the positive electrode. It is also observed underneath lead sulfate layers at the surface of the positive active material. 

Basic sulfates are intermediate compounds that contain lead oxide and lead sulfate and to some extent also water (Table 1). They are stable only in alkaline environment. 

In individnal cases, anodic polarization of metals in electrolyte solntions will pro-dnce snrface layers (adsorbed or phase) which instead of oxygen, contain the soln-tion anions. Thns, anodic polarization of silver in chloride-containing solntions yields a snrface layer of silver chloride, while the anodic polarization of lead in snl-fnric acid solntion yields a lead sulfate layer. Layers of sulhdes, phosphates, and other salts can be formed in the same way. In many respects the properties of such salt layers are analogous to those of the oxide layers. 

The reaction presented above is utilized to leach lead sulfate obtained by thermal oxidation of a mixture of sulfide minerals. The rate of dissolution chemically with a reagent in an... 

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