Arsenic and lead volatilization from molten copper at high oxygen levels
- PDF / 137,165 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 199 Views
In the copper industry, concentrates with low levels of impurity elements are becoming increasingly difficult to locate. The interest in treating high impurity concentrates has led to the development of numerous novel smelting and refining technologies. In addition, mining companies are becoming more concerned with minimizing their atmospheric emissions of sulfur dioxide and heavy metals. Elements such as arsenic and lead are quite detrimental to the environment. In this work, the behavior of these elements was studied under oxidizing conditions (i.e., 1 wt pct oxygen in molten copper). Several researchers have attempted to measure the thermodynamic properties of arsenic in metallic copper. The data available in the literature, however, have been inconsistent.[1,2,3] In the copper industry, the volatilization of arsenic is believed to be mainly due to the formation of AsO during the final copper blow (low S and high O in copper).[4] The vapor pressure of AsO is much higher than that of As, As2, As4, . . . As2O3 or As4O6. Lead volatilization from copper at high oxygen levels should be more predictable than arsenic, since the literature data for the activity of lead and oxygen in copper are more consistent.[1,2] According to thermodynamic calculations, lead volatilization is believed to be due to mechanisms [1] and [2]. [Pb]copper Pbgas
[1]
[Pb]copper [O]copper PbOgas
[2]
The oxygen level in copper influences lead volatilization. Figure 1 illustrates the partial pressure of Pb and PbO at different oxygen levels in copper containing between 0 to 1 pct Pb. When the molten copper contains more than 0.08 wt pct O, the PbO vapor will dominate over the Pb vapor. P. COURSOL, Research Scientist, is with the Arvida Research and Development Center, Alcan International, Jonquière, PQ G7S 4K8, Canada. Contact e-mail: [email protected] N. STUBINA, Six Sigma Master Black Belt, is with Noranda Inc. (Horne Smelter), Rouyn-Noranda, PQ J9X 5B6, Canada. Manuscript submitted October 5, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
For high arsenic and oxygen levels, volatilization is probably due to the formation of AsO, but it may also be due to a gaseous species with unknown thermodynamic properties. As reported by Brittain et al.,[5] there is a surprising number of stable gaseous species in the As-O system, including As4O6, As4O5, As4O3, As2O3, and AsO. If we consider the hypothetical molecule AsxOy to be the main gaseous species involved in the volatilization of arsenic at high oxygen levels in molten copper, the following equation governs its formation: x[As]copper y[O]copper AsxOy (gas)
[3]
The vapor pressure should then be proportional to the following factors: P(AsxOy (gas) ) ([As]xcopper*[O]ycopper )
[4]
Note, when x y 1 (AsOgas), the vapor pressure is proportional to the product of the As and O concentrations. If x and y are greater than 1, then the amount of As reporting to the gas phase will be strongly influenced by the arsenic and oxygen levels in the molten copper. Thermodynamic data
Data Loading...
