To Float or Sink: A Brief History of Flotation Milling

By Dawn Bunyak

ach day metals play an important role in four per cent grade. That means in order to smelt people's lives. Metals make the simple things four million tons of copper, nearly 400 million tons E in life possible. When you turned off the of ore must be removed, milled, and smelted. If met­ morning alarm, rolled out of bed, flipped on the light als, like copper, are so intricately locked in vast switch in the kitchen and turned on the electric cof­ amounts of waste, how is it isolated from that waste? fee pot, you began your day with the assistance of In the twenty-first century, large companies with metals in various products. The car that took you to huge plants continuously work to separate metals work is chock fu ll of metals. The information high­ through the process of flotation. The history of the way that aids you in your daily work is laden with flotation process began in the nineteenth century, base metals. The world is made up of metals and but flotation is considered the most important devel­ metals make up the world. opment of the twentieth-century mining and milling At the beginning of the twentieth century, the industry. world's demand for minerals was minuscule com­ pared to its requirements today. In 1866, a common Flotation electrical generator required fi ve hundred pounds of copper strip and wire. A modern generator contains Flotation is an innovative processing method for approximately fourteen tons for its internal compo­ separating valuable minerals locked in waste rock. It nents. The manufacturing industry requires inordi­ abandons basic principles of ore treatment by gravity nate amounts of metals to produce the luxuries that methods previously followed by early metallurgists. people have come to regard as staples in their day­ At the end of the nineteenth century, the world had to-day lives. almost exhausted its supply of high-grade ore. Min­ So where do metals come from? Mining the ing engineers and inventors worked to create a con­ earth's bounty of minerals began with earliest man's centration method to treat the world's abundant production of tools. Today mining companies re­ supply of low-grade and complex ores, which were move vast quantities of minerals from the earth's often difficult to extract profi tably from waste rock. crust. However, extraction means reduction in the In 1905, the world's first commercially successful flo­ world's minerals supply. Minerals are not replenished tation mill was established at Broken Hill, Australia. as they are extracted. The majority of mines contain Soon, experimental plants in Australia, Great Brit­ metals that are finely disseminated particles in a ain, and the United States also spread the news of mountain of waste rock. For instance, the grade of their success with flotation. Almost overnight, the copper in a ton of rock can be any>vhere from 0.8 to mining industry shifted from exploiting diminishing high-grade ores to an abundant supply of low-grade Dawn Bunyak is a historian with the National Park Srvice in Den­ ver, Colorado. From the coal regions of Central Pennsylvania, her ore. Without the development of the flotation proc­ interest in mining history began with stories of coal mining from ess, metals (such as copper, lead, and zinc) would her grandfather, a coal miner who got his start as a breaker boy in have become increasingly costly and difficult to pro­ the anthracite mines, and her father-in law, also a coal miner. duce causing a direct impact on the global econ- 36 2000 Mining History Journal omy. 1 4. formation of a mineral-laden froth on the Industrialization and flotation propelled the min­ water surface; ing industry into a new age. While earlier concentra­ 5. skimming or floating off the mineral­ tion methods, such as gravity followed by cyanida­ laden froth; and tion, were effective in processing gold ore, flotation 6. drying the resultant concentrate for ship­ opened the minerals market. Metal production was ment to the smelter. 1 increased to twenty-four metallic and nineteen non­ metallic minerals by the mid-twentieth century. Flo­ Flotation greatly differed from earlier mill methods tation can be used in processing metallic orcs (e.g., that used variations of specific gravity. T he most ru­ copper, lead, zinc, gold, silver) or non-metallic ores dimentary form of metal recovery was gravity con­ (e.g., clay, phosphate, coal). Flotation is the most centration. G rav ity concentration used water and widely used process in the world for extracting min­ agitation to sort heavier metals, which settled to the erals. The process also recovers several metals from a bottom, from the waste that rose to the top. single ore body into two or more concentrated prod­ Flotation isolates materials by taking advantage ucts. The development of flotation solved an indus­ of the surface tension of liquids and the ability of try dilemma and allowed increased minerals proJuc­ minerals to attach to air bubbles in liquids.4 Another tion to meet twentieth-century industrial and manu­ innovation of the flotation process is its ability to facturing demands. Modern engineers and inventors alter the pulp chemically (in the water bath or ore assert that the evolution of the flotation process for pulp itself) allowing for an efficient separation of nu­ the recovery of metals was the most important tech­ merous minerals from waste without increasing the nological development of the century. 2 tonnage or grade of ore.' With minor adjustments in the chemicals added to the water bath, the process Flotation Pmcess can be repeated as often as necessary to recover as many different types of metals or minerals from the Flotation is a rnethocl fo r concentrating valuable ore pulp. Flotation, as developed in the twentieth metals from finely ground ores in a water bath, with century, has now become the most widely used proc­ either the ore pulp or water chemically altered with ess for extracting minerals from metallic ores.6 reagents and frothcrs to encourage separation of minerals. The term flotation has been loosely used Development of Flotation for all concentration processes in which heavier mineral particles have been disengaged from lighter N ineteenth-century mill men acknowledged that waste particles in water by "floating" the mineral current milling practices, i.e., crushing, gravity con­ away from waste. Today the term is generally used to centration, and smelting, were not efficiently and describe froth flowcion. Nevercheless it is importanc economically recovering all the mineral wealth from to understand that flotation evolved through three extracted ores. They anticipated that high-grade orcs principal stages of development. These stages will be would soon be depleted. Earlier tnilling methods re­ discussed in more detail later. The process of flota­ covered one mineral or a mineral compound, e.g., tion involves: lead, zinc, or lead-zinc. The dilemma was how tore­ cover various minerals from low-grade ore into a 1. reduction (crushing) of the ore to a size high-grade concentrate. that will free the targeted minerals; Experimentation in flotation of complex ore con­ 2. addition of water, reagents, and frothers, centrates began in England in 1860 ·with William which encourage the minerals to adhere Haynes. Haynes found, when mixing powdered ores, to air bubbles; oil, and water, some minerals had a tendency to at­ 3. creation of a rising current of air bubbles tach to certain oils.7 By the end of the century, many in the ore pulp; others experimented with such variables as: 1) addi- To Float or Sink: A BriefHistOJ)' ofFlotation Milling 37 rives, such as oils, acids, or salts; 2) agitation; and 3) usc of gas bubbles and an altered chemical solution. heat. Several individuals patented their findings in In 1902, Italian Alcide Froment laid claim to the the late 1800s. American Carri e Everson's patents first patent to mention the use of gas for increasing ( 1886 and 1891) included a two-step process dlOr­ buoyancy of metallic particles. A. E. Catrennole's oughly mixing pulverized ore, oil, and an acid or salt patent in England in 1903 used less oil, introduced together into a pulp, then agitating the pulp soap and alkali into the pulp stream, and agitated (crushed ore and oil) on an irregular work surface. In the pulp in a water bath through a continuous earlier experiments, Everson had used a washboard stream of gas bubbles. Although his process was a as a work surface. The metals rose to the top and the commercial failure, Canennole's process is consid­ waste settled in the recessed areas of the washboard. ered the forerunner to flotation methods used to­ ln her patent, Everson listed the minerals she suc­ day.Jl cessfully recovered.s The Wilfley table, developed in 1896, works on the same principal as Everson's ir­ Slsulfide ore based on the princi­ bath. Their process was the forerunner of the Elmore ple of SLilface tension on water. 11 (Sulfide ores can bulk oil process. contain copper, lead, zinc, iron, m.olybdenum, co­ balt, nickel, and arsenic.) The process, con1n1only Bull< Oil Flotation called siFroth Flotation rica, Canada, England, and Wales. 10 Although all rhe Elmore process mills eventually failed, due to The first successful commercial mill using froth excessive amounts of oil that were used, 11 the process flotation was built in 1905 at Broken Hill, Australia, was found in limited usc in Australia as late as 1938. today recognized as the "home of flotation." Inde­ Other experiments in bulk-oil flotation led to the pendent experimentation, based on earlier patents, 38 2000 Miniing Histol)' Journal at Mineral Separation's Broken Hill mines and mills Flotation Circuits resulted in the froth flotation process and the Miner­ als Separation Machine. In 1905, Mineral Separa­ Flotation plants operate through a series of flota­ tion engi11eers, E. L. Sulman, H. F. K. Picard, and tion circuits. Finely crushed and ground ore is intro­ John Ballot, filed a patent for their process that dis­ duced into a water bath in the flotation circuit. In tinguished froth fl otation experiments from sk in and order to achieve separation, an optimum point has bulk-oil flotation. T heir froth flotation process to be met. There are several variables that need to (based on Froment's and Cattermole's earlier pat­ be considered: particle size, reagent additions, pulp ents) used less oil in the ore pulp and added agita­ density, flotation time, temperature of the pulp, type tion by a rising stream of air bubbles. In another of circuit, and water. Next the ore itself must be Minerals Separation mill, a new innovation was the considered: uniformity of the ore, settling and filtt·a­ use of a Minerals Separation Standard Machine, tion data, corrosion and erosion, and finally, the which was a spitz box invented by Theodore J. Hoo­ mineralogy of the ore. 15 O nce all these variables are ver (brother of Herbert Hoover). The pulp passed tested in pilot plants, the concentrator flotation cir­ over the spitz box causing the n1ineral-laden bubbles cuits are designed. to rise to the swfacc. This in turn allowed the col­ Generally, there are two types of separation cir­ lection of mineral-laden froth from the water. The cuits, the simple and the complex. Simple separation Minerals Separation Standard Machine consisted of circuits are generally described as one-product sepa­ a series of cells divided into agitation and frothing rations. A single circuit divides the ore pulp into a compartments. Although it was eventually super­ concenttated ptoduct and ta il ing. In order to process seded as improvements were made to the machine, n1orc than one concentrate, the one circuit mill and Hoover's Separation Machine significantly advanced its workings are periodically adjusted to recycle the m.echanization of the milling industry. ore pulp through the system. After chemically alter­ New technology in crushing and separation of ing the bath or pulp, the process can be repeated as ground ore further advanced the development of flo­ many times as necessary to float off all desired met­ tation. While mechanical classifiers, separation ma­ als. (For a description of a single circuit refer to Fig­ chines, and the W ilfley table assisted in the separa­ ure 1.) tion phase of the flotation process, selective flota­ A complex flotation circuit rends several concen­ tion required finely ground ore (sand or dust) to al­ trates from the ore pulp. Valuable metals arc floated low metals to be recovered on the froth of a water together to form a bulk product. The bulk product bath. Without improved grinding treatment in ball continues its course through a series of flotation cells and rod mills, flotation would not have been possi­ where metals are "selectively" separated into con­ ble. centrates. The waste is sent to a tailing pond. The Inventors Sulman, Picard, and Ballot continued complex or selective flotation circuits are essentially to experiment with soluble frothing agents several cells in a series. The first circuit of cells may (commonly referred to as reagents) and patented remove lead and copper, the second zinc, and the several combinations used at the Broken Hill mills. third an iron reject. Yet, the flow of the pulp Aware that many minerals react d ifferently to re­ through the flotation circuit is continuous. agents in the water bath, experimentation continued Additional operations in the mill include roast­ to create formulas necessary for the separation of ing, steaming, thickening, filtering, leaching, and various minerals. The isolation of desired metals regrinding of the ore pulp in the flotation circuit. 16 would depend on the delicate balance of acid and (For an example of a complex set of circuits, refer to alkaline agents in the flotation process. However, Figure 2, for the flow sheet of the Shenandoah-Dives Minerals Separation's first froth fl otation plant at Mill in Silverton, Colorado.) Plants designed simi­ Broken Hill was a success. larly to the Shenandoah-Dives did not necessarily produce the same concentrate, even on the same To FLoat or Sinle: A Brief Histo1y ofFlotation Milling 39

classifier ·surge tani( 0.-erllow lrom Q clas.;ili~:r-:; in CJ) 20-cell minerals closcdr:;rr:vit separation flotatioo wifll.lxrll mill$ machine G> caJICM' cell (flotanon machtne}

~ cooditicrung tank ®.(§)Q) caliON cellS ·roughing". 'cleamng· & ··recleaning· ® conditioning lank- reagents added CiJ mmerois separation Oolabon machine @. surge lank (!)@X]) caiiCM' cefls iatli'lQ

Fi g . l --Flotation Div ision, Timber Butte Mi ll (A.N. Gaudin, Flotation, (NY: ~1 c Gr a1,;- Hil1 Book Co., 1932), 31.)

ore. Adjustments were made during the process to Commercial Milling allow concentration of different grades of ore. Test­ ing of ore was an on-going process. A circuit can re­ In the early decades of the twentieth centllly, move zinc one day and he adjusted to separate cop­ new patent applications for innovative m.illing proc­ per the next day, depending on the needs of the mill esses were filed almost yearly, in some years even and the mineralogy of the ore it was processing. monthly. From 1910 into the 1920s, litigation, gen­ Flexibility of the concentrator (mill) to simultane­ erally contesting whose idea came first or concerning ously treat various grades of ore improved the mill's wording in patents, tied up courts for years. ability to stay viable in fluctuating markets. Nevertheless, experimentation in flotation con­ Equipment found in a complex circuit may in­ tinued to take place in sn1all plants around the clude: roughers, flotation cells (in many sizes), laun­ world. Sulman, Picard, and Ballot perfected their ders, thickener tanks, regrinders, reagent or frother froth flotation process in a pilot plant in Broken machines, tubes for roasting or heating pulps, pumps, Hill, Australia. American engineer James Hyde trav­ samplers, settling boxes, fi lters, and concentrate eled to Australia in 1911 to study the Broken Hill bins. mills and found four different milling methods in 40 2000 Mining His tory ]oumal

1942 Flow Sheet:

1. 1,200-ton ore bin 2. Pan conveyor. 24" 3. Symons short-head oone ausher 4. No. 86 Marcy grate ball mill 5. Oorr quadruplex classifter 12'x26' 6. No. 64 Sleams-Rogef' ball mil 7. Bucket elevator 3S'x2Z 8. Trash trommel, 9-mesh, 2-112'x6' 9. 8eit elevator 24" 10. Three No.6 Wilfley tables 11. 20-cell No. 21 M.S. flotation 12. 20-cell No. 21 M.S. flotation 13. Uberty Beil type sampler 14. Hydroseal pump, ·e· frame size 15. Wilfley pump, 'Z' 16. Wilfley pump, 'Z' 17. Wilfley pump. 'Z' 16. Wilfley pump. 'Z' 19. Dorr thickener. 35'x10' 20. Steams-Roger baR mill, 4'x10' 21. Esperanza-type classifier. 6'x16' 22. Wilfley pump, 3" 23. Wilfley pump. 3" 24. 8-<:e!l No. 18 Denver flotation 25. Denver condl11oner. 3-1/2'x5' 26. Wilfley pump, 2" 27. 6-cell No. 18 Denver flotation 28. Liberty Bell type sampler 29. Denver 1" com:entrate ptJmp 30. Dorr thickener. 35'x10' 31. Settling box. 3'x6'x2' 32. Dorr filter 2-1/2'x6' 33. Dorr fllter S'x10' 34. Table concentrate bin 35. Zn concentrate bin 36. Pb-Cu concentrnle bin 1'0 TAJUNG PONti

Fig. 2-Fiotarion Division. Shenandoah-Dives (Mayflower) Mill (Mining World June 1942: 12)

use.17 Mills used either froth flotation, a wet-film By 1914, there were forty-two American mining process, agitation-froth flotation, or the Elmore vac­ companies using froth flotation in their mills. 20 Skin uum.18 Eventually, only froth flotation remained and bulk-oil flotation soon became obsolete. The economically viable. first mill to use only the flotation process was the In August 1911, James Hyde experimented with Engels Mine and Mill in Plumas County, California froth flotation in the Basin Reduction Company in 1914.21 ln 1914, J. M. Callow at Miami Copper Mill in Basin, Montana. Butte and Superior Copper Company in Arizona developed and marketed his Company for Hyde's experiments leased the Basin own version of pneumatic flotation cells, similar to Mill. When the lease expired in 1912, Bune and Su­ the Minerals Separation Standard machine.22 Metal­ perior designed and built a mill at the Black Rock lurgists continued to experin1cnt with reagent usc on Mine in Butte, Montana. This mill was recognized as a variety of orcs in the froth flotation process. the first commercial froth-flotation plant in the Chemical agents, acid or alkaline, in the flotation United States. The fac ility used gravity concentra­ process affected metal recovery in various ore bodies. tion in the first three stages anc.l froth flotation in its The Sunnyside Mill at Eureka, San Juan County, final stage. 19 Colorado was credited in 1918 with perfecting the To Float or Sink: A Briefl-listmy ofFlotation Milling 41 flotation of two minerals (lead-zinc) from a complex American industries. 26 ore.!i C. H. Keller introduced xanthates (water­ By the 1930s, froth flotation allowed mining and soluble froth collectors) into water baths in flotation mill ing companies ro recover low-grade ore and by­ circuits in 1925.24 In 1932, G. K. Williams intro­ products once considered waste for profit. Construc­ duced the first continuous refining process.25 How­ t ion of poly-metallic mills allowed the separation of ever, the fundamentals of flotation had already been more than one metal in a series of flotation circuits. established by the end of the 1920s. Single circuit plants continued to be useful in many T he development of flotation had a major impact regions. New poly-metallic mills were larger in size, on the mining world. In concentration, flotation re­ generally processing 750 to 2,000 tons per day to ac­ placed several of the earlier methods: grav ity con­ commodate multiple circuits and ore bins. Finan­ centration, amalgamation , and leaching. In his 1932 cially strong companies in the industry made a move text, Flowtion, A. M. Gaudin attributed major to consolidate mineral patents. Mills and their changes in mining and milling n1etals to the devel­ equipment also expanded in size and processing ca­ opment of flotation concentration. Flotation, in fact, pability. By the 1940s, mining companies also in­ had increased recovery and grade of concentrates creased their use of open-pit mines, ·which greatly and, ar the same time, had decreased the cost of increased the amount of ore extracted. As a result of metal production and the price of metals in the mar­ increased ore extraction, the size of mills grew expo­ ket place. More importantly, Gaudin asserted, flota­ nentially to accommodate ore delivered to the mills. tion increased the manufacturing use of metals in New mills had mu ltiple buildings in complexes that

Shemmdoah-Dives (Mayflower) Mill, S ilverton, San Juan County, Colorado, San Juan County Hisrorical Sociery, Silverron, Colorado. 42 2000 Mining I IisCOl)' ]ortmal covered acres of land. In 1960, 202 flotation plams were operating in Mill expansion resulted in the replacement of the United States. These mills processed metallic obsolete or exhausted operations. By the 1960s, en­ minerals, nonmetallic minerals, bituminous coal, gineers designed larger electric generators, which anthracite, waste paper, nnd miscellaneous materials. allowed for variable speed drives in mills. Even larger Of rl1e metallic-mineral mills, 30 per cent processed sizes of mill equipment cou ld be built and operated copper, lead and zinc. An additional 26 per cent with this increased horsepower. New equipment al­ processed lead-zinc.17 In addition, industries altered lowed for the addition of automatic controls and in­ the flotation process to fit their particular needs, strumentation. When small mills could not be ade­ whether it was non-metallic minerals, coal or paper quately developed, new and larger plants were con­ industries. structed on those sites.

No. 18 Denver Florarion Cells. Interior of Shenandoah -Dive~ Mill, Silverton, Colorado S<1n junn Counry Historic;~ I Society, Silven on, Colorado. To Float or Sink· A BriefHistOI)' ofFlo tation Jvlilling 43

20-Cell No. 21 Minerals Separation Flotation. Interior of Shemmdo

Conclusion allowed non-selective' mmmg and selective milling practices. Miners extracted vast quantities of metals Flotation had a profound affect on the mines and from underground mines, while the mill men ·worked minerals industry, as well as indust1ry as a whole, by to separate valuable metals in th e mill on the sur­ providing all the needed metals at a lower price than face. The mining industry extracted ores that had other•.vise would have been possible. Principally, flo­ minimal quantities of valuable metals, often difficult tation shifted the focus of the mining industry from to extract, locked in tons of waste rock. In the flota­ extraction of high-grade ores to on e featuring com­ tion process, the mill men were able to selectively plex and low-grade ores. W ithout fl otation the min­ isolate metals, wh ich were proHtable or desirable, ing industry would have collapsed by the 1950s. from the waste. Flotation also increased the recovery Flotation essentially reorganized the industry. lt and grade of concentrates without increasing the 44 2000 Mining History ]oumal

tonnage or the grade of the ore. In 1962, mining en­ production with twenty-four metallic and nineteen gineers Charles Merrill and James Pennington wrote non-metallic ores since the commercial success of an essay on new resources available in U.S. flotation flotation in 1905. Many modern engineers believe mills, which was included in Froth Flotation, 50th that flotation was the most important twentieth­ AnniverSaJ)'· T hey found that flotation increased century development in the recovery of metals.

Notes

1. Jeremy Mouat, "TI1e Development of the Flotation Process: and Vincent, Froc/1 Flowcion, 42. Technological C hnnge and the Genesis of Modern Mining, 13. TI1eodore J. Hoover, Concencracing Ores by Flocacion (San 1898-19 11," Ausmrlian Economic HisiOT)' Re11iew 36, no. 1 Fnmcisco: Mining and Scientific Press, 1914 ), 20. (Mnrch 1996): 4. 14. Crabtree and Vincent, Froch Flowcion, 40. 2. "TI1e Trend of Flotation," Colorado School of Mines 15. Adrian C. Dorenfeld, "Flotation C ircuit Design ," in Froch Magazine (January 1930): 20; Mouat, "Development of Flowcion 50ch Annil'crSCil)', 365. Flotation," 4; author's phone interview with Richard 16. Dorenfeld, "Flotation C ircuit Design," 370- 1. Graeme on 10 July 1997 con cerning developments in 17. Dure ll , "Universal Flotation T heory," 29-30. twentieth-century mining; and C harles White Merrill and 18. Durell , "Universal Flotation TI1eory," 29-30; and C rabtree James W. Pennington, "TI1e Magnitude ::md S ignificance of and Vincent, Froth Flocacion, 42-43. For more derails on Flotation in the Mineral Industries of the United S tates," Hyde's famili ::uity with Minerals Separation's process refer in Froth Flowrion 50th AnniFersary (New York: A merican to Pierre Hines and J. D. Vincent=s essay, "The Early Days Institutes of Mining, Metallurgical and Petroleum Engi­ of Froth Flotation," in Froch Flowcion 50'h Anniq,ersm)' Vol­ neering Inc., 1962), 56-57. ume. 3. Flowtion Fundamenwls and Mining Chemicals (Midl}lnd, Ml: 19. Richard 0 . Burt and C hris Mills, Gravity Concemracion Dow C hemic}]! Co., 1968), 8. Techniques (Amsterdam, O xford, New York: Elsevier, 4. Mouat, "Development of Flotation ," 6 and Flowtion Funda­ 1984 ), 17 and Hines and Vincent, "Early Days of Froth mcncals, 11 . Flotation," 12-14. 5. Thom}]S Rickard, Concentration by Flowrion (New York: 20. Hines and Vincent, "Early Days of Froth Flotation ," 29, John W iley and Sons, Inc., 1921), 408. citing G . A. Roush , The Mineral Industry, 1914 (McGraw­ 6. E. H. Crabtree and J. D. Vincent, "Historical O utline of Hill Book Co., New York, 19 15). Major Flotmion Developments," in Froch Flowrion 50th 2 1. Hines and Vincent, "Early D}lys of Froth Flotation," 28. AnniversaT)' Volume, D. W. Fuerstenau, editor (New York: 22. Richards, Textbook of O re Dressing, 234. The A merican Institute of Mining, Metallurgical, and Pe­ 23. Hines and Vincent, "E}l rly Days of Froth Flotation," citing troleum Engineers, Inc., 1962), 39. Editorial, Engineering (md Mining joumal 125 (Feb. 4, 1928): 7. Robert Richards, Textbook of Ore Dressing (New York & 195. London: McGraw-Hill Book Co., Inc., I 932), 233, and 24. C rabtree and Vincent, "H istoricill O utline," 45. C rabtree and Vincent, "Historical O utline," 39. 25. Cedric E. G regory, A Concise Hisror)' of Mining (New York: 8. Rickard, a leading engineer in twentieth-century mining, Pergamon Press, 1980), 140. disputed Carrie Everson's stature as an innovator in the 26. A. M. Gaudin, Flocacion (New York: McGraw-Hill Book milling world. He did not disclaim her findings, but was Co., Inc., 1932), 534. distressed that the findings were attributed to Carrie Ever· 27. Merrill }lnd Pennington, "TI1e Magnitude and SignificmKe son. Ricknrd wrote several articles discussing the topic in­ of Flotmion ," 56-57. cluding an article called, "Everson Myth" in the January 28. Flotation is used in the processing of copper, copper· I 5, 19 16 issue of the Mining and Scientific Press. Rickard was molybdenum, copper-leilcl-zinc, copper-zinc-iron-sulfur, editor of the journal. gold-silver, lead-zinc, barite, bastnilesite, calcite, garnet, 9. Crabtree and Vincent, Froth Flowrion, 40. kym1ite, and tillc. Clay, feldspar, micil, qwutz, spoclumene, 10. Rickard, Concentration, 8. waste paper me processed by fl owtion. Flomtion conce n­ 11. C. T erry Durell, "Universal Flotation TI1eory," Colorado trmes fluorspar, glass sand, ilmenite, magnesite, iron oxide, School of Mines Maga zine 6 (February 19 16): 27. manganese, tungsten, phosphme, <'! nthracite, bituminous 12. Durell, Colorado School of Mines Magazine, 28; and C rabtree coal, chicle, naph thillene and oil.