Deposition copper oxides

Large copper ore deposits are found in the U.S., Chile, Zambia, Zaire, Peru, and Canada. The most important copper ores are the sulfides, the oxides, and carbonates. From these, copper is obtained by smelting, leaching, and by electrolysis. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

In addition to the requirement to conform to steam purity needs, there are concerns that the boiler water not corrode the boiler tubes nor produce deposits, known as scale, on these tubes. Three important components of boiler tube scale are iron oxides, copper oxides, and calcium salts, particularly calcium carbonate [471-34-1]. Calcium carbonate in the feedwater tends to produce a hard, tenacious deposit. Sodium phosphate is often added to the water of recirculating boilers to change the precipitate from calcium carbonate to calcium phosphate (see also Water, industrial water treatment). 

Copper ore minerals maybe classified as primary, secondary, oxidized, and native copper. Primaryrninerals were concentrated in ore bodies by hydrothermal processes secondary minerals formed when copper sulfide deposits exposed at the surface were leached by weathering and groundwater, and the copper reprecipitated near the water table (see Metallurgy, extractive). The important copper minerals are Hsted in Table 1. Of the sulfide ores, bornite, chalcopyrite, and tetrahedrite—teimantite are primary minerals and coveUite, chalcocite, and digenite are more commonly secondary minerals. The oxide minerals, such as chrysocoUa, malachite, and azurite, were formed by oxidation of surface sulfides. Native copper is usually found in the oxidized zone. However, the principal native copper deposits in Michigan are considered primary (5). 

A routine inspection of the tube bundle during a plant outage revealed fine cracks of the type shown in Fig. 9.11. Scattered longitudinal cracks were observed along the lengths of most tubes. The external surface was covered with a thin film of black copper oxide and deposits. The bundle had been exposed to ammonia levels that produced 14 ppm of ammonia in the accumulated condensate. 

A salt bridge serves as an ionconducting connection between the two half-cells. When the external circuit is closed, the oxidation reaction starts with the dissolution of the zinc electrode and the formation of zinc ions in half-cell I. In half-cell II copper ions are reduced and metallic copper is deposited. The sulfate ions remain unchanged in the aqueous solution. The overall cell reaction consists of an electron transfer between zinc and copper ions ... 

Bunsenite (NiO), a nickel oxide, is often found in deposits (albeit only in low concentrations) with zinc and copper oxides as a result of the corrosion of brasses and cupronickels. 

Copper (Cu) is deposited in boilers either by direct exchange with iron or by the hydrogen reduction of copper oxide during the corrosion of steel. 

In addition, the development of porous deposits on boiler surfaces often is enhanced by the presence of small amounts of iron or copper oxides (usually originating from contaminated condensate). This increased rate of deposition may then lead to even more serious problems of overheating. 

Vaporous copper may be particularly damaging because it forms cuprous and cupric oxide deposits on turbine blades. 

NOTE Denting is a phenomenon affecting tubes and tube supports. It is caused by the buildup of voluminous metallic oxides (such as copper oxide from FW heaters and iron oxide from carbon steel components), plus chloride ions. The deposit buildup distorts equipment and causes dents. 

When present as a minor constituent, iron oxides typically impart a tan to brown color to the overall deposit. When iron oxides are present as a major constituent, the color is red-brown to black. Where iron oxides are found, copper oxides usually are also present (typically at 10-15% of the amount of iron oxide concentration). 

Localized deposits containing copper and copper oxides demand a high local concentration of thiourea, and if an inadequate excess of thiourea is present to complex the cuprous ion, precipitation of the insoluble, white copper-thiourea monochloride salt may occur. 

As the overall concentration of copper and copper oxides in the boiler deposit increases, however, less thiourea is required. This is because, as ferric ions are generated during the iron oxide dissolution process, they oxidize the plated copper, which can then be removed from the boiler by forming a complex with thiourea. Conversely, if ferric ions are not generated, the plated copper remains and no complexing can take place. 

The acetylacetonates are stable in air and readily soluble in organic solvents. From this standpoint, they have the advantage over the alkyls and other alkoxides, which, with the exception of the iron alkoxides, are not as easily soluble. They can be readily synthesized in the laboratory. Many are used extensively as catalysts and are readily available. They are also used in CVD in the deposition of metals such as iridium, scandium and rhenium and of compounds, such as the yttrium-barium-copper oxide complexes, used as superconductors. 1 1 PI Commercially available acetyl-acetonates are shown in Table 4.2. 

The deposition of thin films of the high-temperature superconductor yttrium-barium-copper oxide, YBa2Cu307, is obtained from the mixed halides, typically YCI3, Bal2, and CUCI2, with O2 and H2O as oxygen sources. Deposition temperatures are 870-910°C.f ]... 

Table 14.2 lists the principal copper-oxide complexes now under development and their properties. The CVD reactions used to deposit these materials are described in Ch. 11. 

Enriched metal concentrations in the form of secondary enrichment often occur under zones of supergene oxidation and residual concentrations. Gossans, formed over copper and iron bearing sulfide deposits, often overlie zones of secondary enrichment in the form of secondary copper sulfides, and porphyry copper ore deposits very often contain such zones of secondary enrichment. 

Nair, M. T. S. Guerrero, L. Arenas, O. L. Nair, P. K. 1999. Chemically deposited copper oxide thin films Structural, optical and electrical characteristics. Appl. Surf. Sci. 150 143-151. 

Citrosolv A two-stage process for removing deposits from steam boilers, using citric acid. The first stage uses ammoniated citric acid at pH 3.5 to 4 to remove iron oxide the second uses a solution containing more ammonia, pH 9.5 to 10, to remove copper oxide, and an oxidant such as sodium nitrite to passivate the surface. 

Beaudoin, G. Dupuis, C. 2009. Iron-oxide trace element fingerprinting of mineral deposit types. In Corriveau, L. Mumin, H. (eds) Exploring for Iron Oxide Copper-Gold Deposits Canada and Global Analogues. Geological Association of Canada, Short Course Volume, 19, 107-121. 

Corriveau, L. 2007. Iron oxide copper-gold deposits a Canadian perspective. In Goodfellow, W.D. (ed) Mineral deposits of Canada a synthesis of major deposit-types, district metallogeny, evolution of geological provinces, and exploration methods. Geological Association of Canada, Mineral Deposits Division, Special Publication, 5, 307-328. 

Copper oxide gold ores. Although this ore type is not abundant, they are of significant value because they contain gold. Only a few deposits in Brazil and Australia are known. The copper in these ores is represented by cuprite, native copper, antlerite and tenorite. The gold is associated with cuprite, as an auricupride and several sulphosalts. The major problem associated with treatment of this ore type is the presence of large amounts of clay slimes in the form of iron hydroxide and illite. 

The kinetics of chromium (III) oxide deposition from solution during the leaching of skeletal copper has been studied, and a linear rate was found that is not affected by chromate concentration but decreases with increasing hydroxide concentration [55], The total amount deposited was greater as the chromate concentration increased. 

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