(23) Greenberg, R. R.; Gordon, G. E.; Zoller, W. H.; Jacko, R. B.; Neuendorf, D. W.; Yost, K. J. Enuiron. Sci. Technol. 1978, 12, 1329. (24) Friedlander, S. K. Enuiron. Sci. Technol. 1973, 7, 235. (25) Gladney, E. S. Ph.D. Thesis, University of Maryland, College Park, MD, 1974. (26) Gordon, G. E.; Zoller, W. H.; Gladney, E. S. Trace Subst. Enui-
ron. Health 1973, 7, 167-74. (27) Gordon, G. E. Enuiron. Sci. Technol. 1980,14, 792. Received for review October 12, 1979. Accepted November 7, 1980. This work was supported by the National Science foundation RANN Program under Grant Nos. ENV 75-02667-A03 and PFR 7502667806
Fractionation of Elements during Copper Smelting Mark S. Germani,t Mark Small,* and William H. Zoller" Department of Chemistry, University of Maryland, College Park, Maryland 20742
Jarvis L. Moyers Department of Chemistry, University of Arizona, Tucson, Arizona 85721 H Large enrichments, relative to crustal material, of many chalcophilic elements, e.g., As, Se, Pb, Cd, Zn, W, and In, have been reported for particulate material emitted from copper smelters located in southeastern Arizona. There is also a significant difference in the enrichments for certain elements emitted from different copper smelters. This papef reports results of a study of in-plant material collected at five copper smelters in Arizona. The samples were analyzed by instrumental neutron activation analysis and atomic absorption spectrometry for up to 35 elements. Large enrichments of the chalcophilic elements are due to their volatilization during copper smelting. Variations in the elemental enrichments among the smelters appear to be due to differences in the feed material, smelting conditions, and equipment used by the comer smelters.
Introduction Recently a study was made of the elemental composition of particulate material collected in the plumes of five copper smelters in southeastern Arizona ( I ) . Many elements are highly enriched in the plume material relative to the background aerosol, and there are significant differences in the chemical composition of particles emitted by the various copper smelters. In this paper we examine the feed material and in-plant processes in order to identify factors responsible for the high enrichments of some elements in plume particles and the large plant-to-plant variation of particle composition. Ores containing typically less than 1%copper are used for smelting. The ore is transported from the mine to a crushing and milling plant where it is reduced to a fine powder. The copper-bearing minerals are removed from the ore by froth flotation. This involves adding a flotation agent to a water suspension of the ore material, causing the sulfide minerals to float to the surface where they can be skimmed off. The copper minerals are then removed by settling, followed by filtration and drying. This copper concentrate is the feed material for the smelting process. Molybdenum sulfide minerals are separated from the ore in a similar fashion but kept separate from the copper concentrate. Ores which contain
+ Present address: Chemistry Department, Arizona State Universit ,Tempe, AZ 85281. ?Present address: Midwest Research Institute, Kansas City, MO 64110.
0013-936X/81/0915-0299$01.25/0
@ 1981 American Chemical Society
copper oxide minerals are leached with acid, and the precipitate is used as the feed material. Some smelters also add their revert material, e.g., precipitator dusts, and byproducts from other smelting operations to the copper concentrate. The smelting operation consists of four processes: roasting, smelting, converting, and anode casting. Eight of the sixteen copper smelters in the U.S.pretreat the concentrate by roasting it in either fluidized-bed or multiple-hearth roasters to remove some of the sulfur as sulfur dioxide. The temperature may vary during roasting, but it does not exceed the melting point of the material (-1000 "C). The roasted concentrate (calcine) or "green" (unroasted) concentrate is then added to a reverberatory furnace along with silica and/or limestone which is used as a flux. The temperature (-1500 "C) and the oxidizing conditions in the furnace cause some of the iron and sulfur to be converted to oxides, whereas the copper and some iron remain in the sulfide form. The material separates into essentially two phases: the higher-density sulfide portion (matte) which sinks to the bottom and the iron oxide and flux (slag) which remains on top. The matte ususlly consists of about equal portions of copper and iron sulfides. The matte is drawn from the bottom of the furnace and transported by ladles to the convertors, where more flux is added. There are two steps in the conversion process. First, the iron sulfides are converted to iron oxides and removed in the slag. Next the copper sulfides are converted to molten copper metal (blister copper), which is -99% copper. The final step is to cast the copper metal into anodes which can later be purified by electrolytic refining. Smelting is not a continuous process. The furnace(s) continuously produce(s) matte; however, the convertors are only used when enough matte has been processed. Most copper smelters use the same general procedure in smelting the concentrate, but operating conditions vary somewhat depending upon several factors, e.g., the composition of the concentrate, the use or not of roasters and the type of roaster used, the quality of matte desired and the type of reverberatory furnace available, etc. These factors, along with the nature of the air pollution control devices used, will determine the size distribution and composition of the particles emitted from the smelters. Samples of concentrate were obtained from five smelters, three of whieh, smelters 1,2, and 5, were included in the plume study ( I ) with the same numerical designations, (1) to determine the variability in the trace-element content of copper concentrates and (2) to see whether this variability is reflected in the elemental concentrations found in the plume particulate material. Samples of ore, precipitator dusts, and in-stack Volume 15, Number 3, March 1981 299
particulate material were also collected from smelter 1and/or smelter 2 to determine the extent of elemental fractionation during the mining and smelting of copper ores. Instrumental neutron activation analysis (INAA) and atomic absorption spectrometry (AAS) were used in the analysis of the samples for -35 elements. Special emphasis was placed on the volatile elements that are usually associated with sulfide ores, e.g., As, Se, Sb, Cd, In, Zn, and Pb.
Sample Collection and Analysis The copper companies provided samples of ore (smelter 2), concentrate (smelters 1-5), and precipitator dust (smelter 1: reverberatory furnace and convertor precipitator dust; smelter 2: reverberatory furnace precipitator dust). These samples were collected simultaneously with the plume sampling described in ref l . In-stack particulate material was collected a t smelter 1 by using a modified EPA sampling train (2). Samples were collected after the electrostatic precipitator a t a port in the reverberatory furnace stack located -30 m above ground level. Ten whole-filter samples were collected for 10-20
min a t a temperature of -130 "C and an isokinetic flow rate of -15 L/min. Six samples were obtained by using quartz-fiber filters (Pollflex Corp., Putnam, CT), and four samples were collected by using 1.0-pm Fluoropore filters (Millipore Corp., Bedford, MA). During three of the quartz-fiber-filter collections, a charcoal trap was placed a t the end of the probe external to the stack to collect vapor-phase arsenic and selenium. Two of the traps contained 1g of precleaned activated charcoal and the other contained 3 g. A detailed description of the use of charcoal for the collection of vapor-phase species is given elsewhere ( 3 ) .The stack sampling was carried out over a 2-day period (March 29 and 30,1978) simultaneously with the aircraft plume sampling a t this smelter. Samples were analyzed by INAA a t the University of Maryland and by AAS a t the University of Arizona. The ore, concentrates, and precipitator dusts were dried over PzO5 for 1week. Four replicate analyses were done for each sample. Ca. 50 mg of sample was weighed into a precleaned polyethylene bag and irradiated in a neutron flux of 1 X 1013n/(cmz s) along with the appropriate elemental monitors a t the National
Table 1. Elemental Concentrationsdin Concentrates from Five Copper Smelters element
Li Na Mg AI ( % ) Si ( % ) s (%) K Ca(%) sc V Cr Mn Fe(%) co c u (%) Zn As Se Rb Sr Ag Cd In Sb
cs La Ce Sm Eu Yb
Lu Hf
Ta
w Au Pb Th a
smelter 1
smelter 2
Average enrichment factor (with respect to AI).
300
smelter 3
smeller 4
smelter 5
4.6 f 0.4 4.9 f 0.5 11 f 1 6.8 f 0.7 19 f 2 1450 f 250 1050 f 60 1030 f 60 630 f 30 330 f 70 1160 f 120 710 f 70 1550 f 150 3400 f 300 16000 f 2000 0.78 f 0.11 0.59 f 0.08 1.5 f 0.3 1.08 f 0.05 0.19 f 0.02 2.8 f 0.3 2.3 f 0.2 4.5 f 0.5 4.9 f 0.5 3.7 f 0.4 26 f 2 30f 9 23f 1 25 f 5 28 f 4 4100 f 800 4100 f 1500 7700 f 130 5200 f 700 730 f 70 0.28 f 0.11 0.19 f 0.04 0.22 f 0.07 0.35 f 0.08 0.71 f 0.09 4.6 f 0.1 0.31 f 0.02 2.1 f 0.3 1.3 f 0.1 1.1 f 0.2 45 f 4 5.4 f 1.3 14f2 l l f 2 13 f 4 33 f 2 8.9 f 0.6 14f 1 53 f 3 5 f l 200 f 20 420 f 70 220 f 20 25 f 2 26 f 3 25.9 f 0.3 25.5 f 0.4 19.8 f 0.7 25 f 2 28 f 2 44 f 1 293 f 5 1 9 0 f 12 122 f 6 160 f 13 24.0 f 0.5 18.0 f 0.8 25 f 4 23 f 3 27 f 4 18400 f 100 1800 f 200 2700 f 400 700 f 65 200 f 60 540 f 30 510 f 40 380 f 14 8 3 f 17 1270 f 170 100 f 2 140 f 4 220 f 14 200 f 10 190 f 4 24 f 2 30 f 8 27 f 9
