Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Introduction Lead is a rare element present in the earth’s crust in a 1.4 Â 10À3% (w/w). It is a toxic heavy metal that exists only in a cubic close-packed metallic form. It shows the preference for the divalent state with electronic configuration [Xe]4f145d106s2 and low stability of the Pb–Pb covalent bond. Lead(IV) in solution is unstable (electronic configuration: [Xe]4f145d10). The most important Pb ore is galena (PbS). Other lead ores are anglesite (PbSO4), cerussite (PbCO3), mimetesite (Pb5(AsO4)3Cl), and pyromorphite (Pb5(PO4)3Cl). . | Lead K Maksymiuk J Stroka and Z Galus University of Warsaw Warsaw Poland 2009 Elsevier B.V. All rights reserved. Introduction Lead is a rare element present in the earth s crust in a 1.4 x 10 3 w w . It is a toxic heavy metal that exists only in a cubic close-packed metallic form. It shows the preference for the divalent state with electronic configuration Xe 4f145d106s2 and low stability of the Pb-Pb covalent bond. Lead IV in solution is unstable electronic configuration Xe 4f145d10 . The most important Pb ore is galena PbS . Other lead ores are anglesite PbSO4 cerussite PbCO3 mimetesite Pb5 AsO4 3Cl and pyromorphite Pb5 PO4 3Cl . Chemistry of Lead Lead is usually obtained from galena. After concentration by flotation PbS is converted in the presence of air to PbO PbS 1.5O2-PbO SO2 I which is mixed with coke and limestone and reduced in the blast furnace according to the reactions PbO C-Pb liq CO II PbO CO - Pb liq CO2 III Lead may also be produced by the reduction of the roasted ore with fresh galena PbS 2PbO - 3Pb liq SO2 g IV Such obtained Pb contains several metal impurities such as Cu Ag Au Zn Sn As and Sb which have to be removed. The final purification is carried out by electrolytic rafination using massive cast Pb anodes. This procedure yields a cathodic deposit with 99.99 Pb. It can be further purified electrochemically to obtain Pb with impurities level below 1 ppm. Pure lead is silver-gray very soft and low-melting metal with a high density which can be easily hammered. Lead is used in the production of batteries cable sheathing sheets pipes foils tubes solders pigments and chemicals. The physicochemical and atomic properties of metallic lead are presented in Table 1. Finely divided Pb powder is pyrophoric. The reactivity of lead at ambient temperature is usually inhibited by the formation of protective layers of insoluble products such as oxide carbonate or sulfate on the surface. The lead reacts with fluorine at room temperature to give PbF2 whereas .
