AluniteROBERT B. HALL CHARLES W. BAUERxc
Alunite, KA1, (SO,) ,(OH) , , was used from the 15th century until early in the present century as a source of potash alum and aluminum sulfate. Since early in this century its use for this purpose has declined to virtually nil with acid treatment of bauxite or clay replacing alunite as a source of alum. During the First World War alunite served as an emergency source of potassium sulfate fertilizer in the United States and Australia. More recently, alunite has been investigated as a nonbauxite ore of aluminum, with potassium sulfate and sulfuric acid as recoverable byproducts. The Soviet Union established a commercial-scale plant in the mid-1960s producing cell-grade alumina from alunitic ore and recovering byproduct potassium sulfate and sulfuric acid. Interest in nonbauxite ores, including alunite, is expected to continue in countries that presently are dependent on imports of bauxite or alumina to support their aluminum industries. The US has the largest aluminum producing and fabricating industry in the world but imports more than 90% of its aluminum-bearing raw materials. This chapter reviews the status of alunite as a potential source of aluminum with byproduct fertilizer, and the resources available to support this industry, whenever this becomes economically feasible.
Historical BackgroundAlunite has received little attention until recently, yet for centuries it held a higher place than many of the industrial minerals considered essential today. The deposits of alunite at Tolfa, northwest of Rome, were mined
* Geologist, Branch of Central Mineral Resources, US Geological Survey, Denver, CO. t Senior Project Manager-Geologist, Earth Sciences, Inc., Golden, CO.
almost continuously from 1462 until about the middle of the present century (DeLaunay, 1907; Lombardi, 1977). The potash alum made from the alunite, called Roman alum, was a valued commodity in international trade, being used in the making of paper, in tanning leather, and as a mordant in textile dyeing. The industry at Tolfa is said to have been controlled by the Vatican and was a source of revenue for the Papal State until fairly recent times (Lombardi et al., 1977). Since early in the present century, the preferred method for making alum has been by acid treatment of bauxite, clay, or other aluminous material, so that alunite has fallen into near-total disuse as a source of alum chemicals. Appreciable quantities of mixed alunite-kaolin rock still are quarried in the Tolfa district for use by the Italian cement industry (Lombardi and Mattias, 1979), but the role of this material in the making of Italian cement is not clear. A large deposit of alunite-bearing rock in Chekiang province, mainland China, is said to have yielded a "great quantity" of alum over a period of several centuries (Yih, 1931). During the 19th century, alunite deposits in France, Spain, Australia, and other countries were exploited as raw material for making potash alum and aluminum sulfate. Interest in alunite was revived during the First World War, not for alum, but as an emergency source of potassium sulfate fertilizer. Large veins of nearly pure alunite had just been discovered on Alunite Ridge, 11 km southwest of Marysvale in Piute County, Utah (Butler and Gale, 1912), and these were quickly brought into production for making potash fertilizer to replace supplies cut off from the famous deposits at Stassfurt, Germany. An estimated 225 kt of Marysvale alunite was mined and processed at that time (Callaghan, 1973). Similarly, Australian alunite deposits were mined as a source of potash fertilizer during both world wars (Hall, 1978).
Industrial Minerals and Rocksnot been scheduled as of 1982, but may proceed if technological breakthroughs are achieved or if costs of imported bauxite and alumina rise to levels at which use of alunitic rock becomes more attractive economically. Obsolescence and aging of conventional Bayer plants designed to operate on imported bauxite also may become a factor contributing to development of nonbauxite ores. Costs of new greenfield plants fed by domestic alunite may compare favorably with new Bayer plants fed by imported bauxite, when all factors are considered. Alunite one day may be regarded by the aluminum industry in much the same way that taconite now is regarded by the steel industry.
Shortly before entry of the US into World War 11, a comprehensive review of the US alunite resources was made by the US Bureau of Mines (USBM) (Thoenen, 1941) . Thoenen recognized the deposits at Marysvale as the most promising then available to American industry and, after the entry of the US into the war, efforts were accelerated to explore the deposits and to develop a method for economically processing the ore to produce aluminum (Fleischer, 1944; Hild, 1946; Callaghan, 1973). Japan also experimented with alunite as a wartime aluminum ore (Allen, 1947). With the end of the wartime emergency, alunite was relegated to the status of an unpromising, noneconomic resource (Anon., 1970) and was all but forgotten. The Soviet Union, as a matter of national policy aimed at raw material self-sufficiency, established a 200 kt/ a aluminafrom-alunite plant in the state of Azerbaijan in the mid 1960s. The Soviet Union, like the United States, is deficient in bauxite resources (Shabad, 1976). US interest in alunite was revived in 1970 when large resources of alunitic rock were discovered 140 km west of Marysvale by personnel of Earth Sciences, Inc., ~ b l d e n , CO. The deposits, located in the southern Wah Wah Mountains of Beaver County, Utah, 87 km northwest of Cedar City, were explored by trenching and drilling. A proven-plus-probable' reserve of 136 Mt of rock containing about 38% alunite, with an additional inferred reserve of 500 Mt of similar grade, was announced (Anon., 1976). Pilot-plant testing was conducted at Golden, C O from November 1973 until the end of 1976 by the Alumet consortium comprising Earth sciences, Inc., National Steel Co. of Pittsburgh, PA, and the Southwire Co. of Carrollton, GA. The preferred process is generally similar to that used by the Soviet Union (Thompson, 1976). The Alumet partnership announced intent to establish an alumina-from-alunite industry in southwest Utah with a capacity to produce 454 kt/a of cell-grade alumina with 227 kt/a of fertilizer-grade potassium sulfate and 408 kt/a of industrial-grade sulfuric acid as byproducts. The plan called for calcined phosphate rock to be shipped by rail to the Utah plant site from deposits in southeastern Idaho and to be treated with the acid to produce phosphate fertilizer. Sale of two fertilizer byproducts would considerably enhance the economics of alumina production from low-grade alunite-bearing rock (Walker and Stevens, 1974; Parkinson, 1974; Thompson, 1976). Construction of the Alumet project still had
GeologyAlunite occurs in a variety of deposits ranging in size from mere nodules and lenticles a few centimeters across to huge masses comprising several hundreds of millions of tons of altered rock containing 30 to 40% alunite. Nearly pure alunite occurs in hypogene veins.Classification of Deposits
Three main classes of alunite deposits are commonly recognized (Hall, 1978, 1980) : Veins: The veins at Alunite Ridge, Marysvale, U T are steeply dipping fissure fillings with sin~~ou trend s enclosed in strongly altered volcanic lava flows, mud flows, and ash-flow tuffs (Butler and Gale, 1912; Callaghan, 1973). DeLaunay (1907) described veins at the classic deposits at Tolfa, Italy that are similar to those at Marysvale. Veins several meters wide and several hundred meters long provided the bulk of the alunite production at Tolfa (DeLaunay, 1907). Lombardi (1977) reports an estimated total production at Tolfa of 18 Mt during a span of five centuries. Callaghan (1973) reports an estimated production of 225 kt from veins at Marysvale during the First World War. Veins smaller than those at Marysvale occur in Lincoln, Mineral, and Humboldt counties, Nevada, and Yuma County, Arizona, with tenor ranging from 75 to nearly 100% alunite. Alunite veins may be white to yellow cryptocrystalline, or may contain coarse pink crystals 10 to 20 mrn long. Although the high-grade alunite in veins almost certainly would be an acceptable substitute for bauxite, the total resource available in veins is too small to constitute a raw material base for industry. Nodules and seams in argillaceous sedimentary rocks: Nodules and thin discontinuous
Alunitelayers and seams of alunite or natroalunite are surprisingly common and widespread geographically (Hall, 1978), occurring in shales, micaceous schists, or clayey beds. They appear to have been formed supergenically or diagenetically by the action of sulfate-rich acid ground water on illitic or mica-rich argillic sediments. Oxidation of pyrite disseminated in adjacent or superjacent rock provides the necessary acid; potassium is derived from illite or muscovite mica in the alunitized host sediment. The purity of alunite nodules may approach that of veins, but these sedimentary occurrences are, for the most part, confined to thin discontinuous layers commonly intermixed with kaolin, and do not form bodies large enough to serve as an aluminum resource. An unusual sedimentary deposit at Lake Campion, near Chandler, Western Australia, was mined during World War I1 as a source of potassium sulfate fertilizer. The lake sediment contains 60% alunite. The balance is mostly detrital quartz, mica, and iron oxide. Reserve was estimated at 12 Mt (Fitzgerald, 1945). The origin of this deposit is not clear, but it may have been formed by a diagenetic mechanism similar to that postulated by King (1953) to explain alunite-rich lake sediment at Pidinga, South Australia. The Australian lake deposits, although much larger than most sedi