L.
P.Argenbright and Bennett Preble
Arthur G . McKee & Co. Western Knapp Engineering Division San Francisco, California
SO, from smelters:
Threeprocesses1 overview of recov
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U o m e 2.2 million 'long tons per year of sulfur is contained in the sulfur oxide gases generated in the operation of copper, zinc, and lead smelters in the western US.Nearly 23% of this is recovered, almost all as sulfuric acid. More acid can be made where markets are available, but many smelter gas flows are too dilute for economic acid manufacture. Costs for concentration of these gases by presently known processes are excessive. To make clear the technological and economic factors bearing on the problem of controlling these sulfur oxide emissions, we undertook a study of primary copper, zinc, and lead smelting operations. A necessary first step was to learn how much sulfur oxide was being generated, how much was recovered in any form, and how much was getting into the atmosphere. More knowledge was needed about the sources of emissions in the smelters, about the concentrations of the gases, and about the problems involved in controlling emissions, as well as ahout the methods for sulfur oxide recovery now in use or available for use. Technical personnel familiar with the industry visited the smelters in 1968 to obtain such information as the amount of sulfur entering each plant in sulfide ore concentrates, and the amount leaving in gases at major 554 Environmental Science & Technology
Smelter. Almost half a million t o m of sulfur is recovered every year f r o m western smelters, but three times (1s much is still discharged into the air
feature
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Contact sulfuric acid process
operating steps. We also looked into the volumes of gases generated or emitted from the various sources, gases fed to recovery units, stack gases, amounts of recovered by-products, and sulfur remaining in the solid residues. No actual measurements or analyses were made during the visits, so the information obtained was limited to what could be made available from operating files at each smelter. After this information had been gathered, material balances were calculated for each plant. The complexity of operations at copper smelters is such that satisfactory balances for these plants required the development and use oE a computer program. The figures obtained should not be viewed as absolute, for in some areas information available was incomplete and may have been inaccurate. In compiling the statistics. allowance was made for changes in smelter operations planned for the last part of 1968 or the first half of 1969. Two new lead smelters in Missouri are not included in the statistics. A total of approxiniately 2,165,000 long tons of sulfur is contained in the sulfur oxide gases generated annually at the U S . copper, zinc, and lead smelters west of the Mississippi River. Of this, 491,000 long tons or 22.7% is recovered; 487,000 tons as sulfuric acid and 4000 tons as liquid sulfur dioxide. The remainder of 1,674,000 tons is emitted to the atmosphere. The quantities of sulfur oxides, in terms of
sulfur equivalent, generated and recovered from various sources are presented in an accompanying table. Weak smelter gases
Recovery of sulfur oxides from smelter gases is difficult because many of the gas streams, at the points where they could be diverted to a recovery process, have been diluted with air and the concentrations of sulfur oxides are low. This has an adverse effect on the recovery operation, since the cost of recovering sulfur oxide is in inverse proportion to its concentration in the gas stream.
An obvious remedy is to develop smelter practices to prevent dilution of the gases with air. This has been done at smelters that have found markets for by-product sulfuric acid made from recovered sulfur dioxide. Not all weak gases can be eliminated in this way, however, and additional recovery of sulfur will be favored by development of processes to extract and concentrate sulfur oxides from weak gas streams at low cost. Many such processes have been proposed, but few have been described in enough detail to give a sound basis for cost estimation.
Sulfur Oxide Generation and Recovery in Western Smelters. Generated Recovered
