petroleum refineries. In the latter case, most (0.958 MMT) of the sulfur was used on site, but almost half of the spent acid (0.43 MMT S) from refineries was later reclaimed. Sulfuric acid was recovered from copper, zinc, and lead smelters (1.125 MMT S), but much of that (0.543 MMT) was used in the acid-leach process of mining operations. In the case of copper mines, copper sulfate is recovered from the leach piles and recycled, but much of the leaching acid remains in the ore heaps, where it presumably reacts with other minerals and remains as insoluble sulfates.
By far the largest use of sulfuric acid is for processing phosphate rock (8.404 MMT S). This use was noted above. Another important use of sulfuric acid (0.288 MMT S) is in the sulfate (Kraft) pulping process, also discussed above. The pickling process used to clean rolled steel prior to galvanizing or tin-plating used 0.074 MMT S as acid, of which 0.022 MMT was recovered. Sulfuric acid containing an additional 0.024 MMT S was used by other metallurgical processes, mainly metal plating. Automotive batteries accounted for a further 0.051 MMT, of which 0.036 MMT was reclaimed. The above uses plus exports add up to 11.162 MMT of embodied sulfur, or greater than 90 percent of the total. The remainder, 1.172 MMT of embodied sulfur, either is used elsewhere in the chemical industry or is used for unidentified nonchemical purposes.
Excluding phosphates and sulfuric acid itself, about 5.04 MMT of sulfuric acid (1.645 MMT S) and 0.684 MMT of elemental sulfur were consumed by the nonphosphate chemical industry in 1988. Industrial inorganic chemicals, including pigments, consumed about 0.9 MMT S, mostly as acid. Of the sulfur used in chemicals, 0.566 MMT was eventually converted into ammonium sulfate fertilizer, mostly as a by-product of other chemical processes that use sulfuric acid (e.g., caprolactam, a nylon monomer, and hydrogen cyanide). Of the rest, 0.170 MMT was embodied in aluminum sulfate, mainly for the paper industry; 0.185 MMT S was in the form of by-product sodium sulfate, consumed in pulp manufacture. Apparently, 0.460 MMT of elemental sulfur was used in "other" agricultural chemicals. The organic side of the chemical industry consumed at least 0.7 MMT S, mostly as acid. Of this, drugs and pesticides accounted for only 0.02 MMT and detergents for 0.06 MMT. The major uses were for the manufacture of organic chemical intermediates and synthetic rubbers and plastics. However, except for drugs, pesticides, and detergents, virtually no sulfur is embodied in organic chemicals. Hence, at least 0.6 MMT S was consumed and lost in organic processing. In addition, there was 0.824 MMT S as sulfuric acid and 0.297 MMT elemental sulfur in the "unidentified and export" category. For reasons discussed below, we believe that most of this was also consumed in the organic chemical industry.
These waste flows were in several chemical forms, including H2S, SO2, ammonium bisulfate, calcium sulfite, and calcium sulfate. (To mention one example, hydrofluoric acid manufactured in 1988 would have accounted for about 0.24 MMT S and generated calcium sulfate waste.)