Flotation processes are described in ancient Greek and Persian literature. During the late 19th century, the process basics were discovered through a slow evolutionary phase. During the first decade of the 20th century, a more rapid investigation of oils, froths, and agitation led to proven workplace applications, especially in Broken Hill, Australia, that brought the technological innovation known as “froth flotation.” During the early 20th century, froth flotation revolutionized mineral processing. Initially, naturally occurring chemicals such as
fatty acids and oils were used as flotation
reagents in large quantities to increase the hydrophobicity of the valuable minerals. Since then, the process has been adapted and applied to a wide variety of materials to be separated, and additional collector agents, including
surfactants and synthetic compounds have been adopted for various applications.
19th century Englishman William Haynes patented a process in 1860 for separating
sulfide and
gangue minerals using oil. Later writers have pointed to Haynes's as the first "bulk oil flotation" patent, though there is no evidence of its being field tested, or used commercially. In 1877 the brothers Bessel (Adolph and August) of Dresden, Germany, introduced their commercially successful oil and froth flotation process for extracting
graphite, considered by some the root of froth flotation. However, the Bessel process became uneconomical after the discovery of high-grade graphite in
Sri Lanka and was largely forgotten. Inventor Hezekiah Bradford of Philadelphia invented a "method of saving floating material in ore-separation” and received US patent No. 345951 on July 20, 1886. He would later go on to patent the Bradford Breaker (US patent No. 143745), currently in use by the coal industry, in 1873. His "Bradford washer," patented 1870, was used to concentrate iron, copper and lead-zinc ores by specific gravity, but lost some of the metal as float off the concentration process. The 1886 patent was to capture this "float" using surface tension, the first of the skin-flotation process patents that were eclipsed by oil froth flotation. On August 24, 1886,
Carrie Everson received a patent for her process calling for oil[s] but also an acid or a salt, a significant step in the evolution of the process history. By 1890, tests of the Everson process had been made at Georgetown and Silver Cliff, Colorado, and Baker, Oregon. She abandoned the work upon the death of her husband, and before perfecting a commercially successful process. Later, during the height of legal disputes over the validity of various patents during the 1910s, Everson's was often pointed to as the initial flotation patent - which would have meant that the process was not patentable again by later contestants. Much confusion has been clarified recently by historian Dawn Bunyak.
First commercial flotation process The generally recognized first successful commercial flotation process for
mineral sulphides was invented by Frank Elmore who worked on the development with his brother, Stanley. The Glasdir copper mine at
Llanelltyd, near
Dolgellau in
North Wales was bought in 1896 by the Elmore brothers in conjunction with their father, William. In 1897, the Elmore brothers installed the world's first industrial-size commercial flotation process for mineral beneficiation at the Glasdir mine. The process was not froth flotation but used oil to agglomerate (make balls of) pulverised sulphides and
buoy them to the surface, and was patented in 1898 (revised 1901). The operation and process was described in the April 25, 1900
Transactions of the Institution of Mining and Metallurgy of England, which was reprinted with comment, June 23, 1900, in the
Engineering and Mining Journal, New York City. By this time they had recognized the importance of air bubbles in assisting the oil to carry away the mineral particles. As modifications were made to improve the process, it became a success with base metal ores from Norway to Australia. The Elmores had formed a company known as the Ore Concentration Syndicate Ltd to promote the commercial use of the process worldwide. In 1900,
Charles Butters of Berkeley, California, acquired American rights to the Elmore process after seeing a demonstration at Llanelltyd, Wales. Butters, an expert on the
cyanide process, built an Elmore process plant in the basement of the Dooley Building, Salt Lake City, and tested the oil process on gold ores throughout the region and tested the tailings of the Mammoth gold mill, Tintic district, Utah, but without success. Because of Butters' reputation and the news of his failure, as well as the unsuccessful attempt at the LeRoi gold mine at Rossland, B. C., the Elmore process was all but ignored in North America. Developments elsewhere, particularly in
Broken Hill, Australia by
Minerals Separation, Limited, led to decades of hard-fought legal battles and litigations (e. g.
Minerals Separation, Ltd. v. Hyde) for the Elmores who, ultimately, lost as the Elmore process was superseded by more advanced techniques. Another flotation process was independently invented in 1901 in Australia by Charles Vincent Potter and by
Guillaume Daniel Delprat around the same time. Potter was a brewer of beer, as well as a chemist, and was likely inspired by the way beer froth lifted up sediment in the beer. This process did not use oil, but relied upon flotation by the generation of gas formed by the introduction of acid into the pulp. In 1903, Potter sued Delprat, then general manager of
BHP, for patent infringement. He lost the case for reasons of utility, with Delpat arguing that while Potter's's process, which used sulphuric acid to generate the bubbles in the process, was not as useful as Delprat's process, which used salt cake. Despite this, after the case was over BHP began using sulphuric acid for its flotation process. In 1902, Froment combined oil and gaseous flotation using a modification of the Potter-Delprat process. During the first decade of the twentieth century, Broken Hill became the center of innovation leading to the perfection of the froth flotation process by many technologists there borrowing from each other and building on these first successes. Yet another process was developed in 1902 by Arthur C. Cattermole, who emulsified the pulp with a small quantity of oil, subjected it to violent agitation, and then slow stirring which coagulated the target minerals into nodules which were separated from the pulp by gravity. The Minerals Separation Ltd., formed in Britain in 1903 to acquire the Cattermole patent, found that it proved unsuccessful. Metallurgists on the staff continued to test and combine other discoveries to patent in 1905 their process, called the Sulman-Picard-Ballot process after company officers and patentees. The process proved successful at their Central Block plant, Broken Hill that year. Significant in their "agitation froth flotation" process was the use of less than 1% oil and an agitation step that created small bubbles, which provided more surface to capture the metal and float into a froth at the surface. Useful work was done by
Leslie Bradford at
Port Pirie and by
William Piper, Sir
Herbert Gepp and
Auguste de Bavay. Mineral Separation also bought other patents to consolidate ownership of any potential conflicting rights to the flotation process - except for the Elmore patents. In 1910, when the Zinc Corporation replaced its Elmore process with the Minerals Separation (Sulman-Picard-Ballot) froth flotation process at its Broken Hill plant, the primacy of the Minerals Separation over other process contenders was assured. Henry Livingston Sulman was later recognized by his peers in his election as President of the (British)
Institution of Mining and Metallurgy, which also awarded him its gold medal.
20th century Developments in the United States had been less than spectacular. Butters's failures, as well as others, was followed after 1904, with Scotsman Stanley MacQuisten's process (a surface tension based method), which was developed with a modicum of success in Nevada and Idaho, but this would not work when
slimes were present, a major fault. Henry E. Wood of Denver had developed his flotation process along the same lines in 1907, patented 1911, with some success on molybdenum ores. For the most part, however, these were isolated attempts without fanfare for what can only be called marginal successes. In 1911,
James M. Hyde, a former employee of Minerals Separation, Ltd., modified the Minerals Separation process and installed a test plant in the Butte and Superior Mill in
Basin, Montana, the first such installation in the USA. In 1912, he designed the Butte & Superior zinc works, Butte, Montana, the first great flotation plant in America. Minerals Separation, Ltd., which had set up an office in San Francisco, sued Hyde for infringement as well as the Butte & Superior company, both cases were eventually won by the firm in the U. S. Supreme Court.
Daniel Cowan Jackling and partners, who controlled Butte & Superior, also refuted the Minerals Separation patent and funded the ensuing legal battles that lasted over a decade. They - Utah Copper (Kennecott), Nevada Consolidated, Chino Copper, Ray Con and other Jackling firms - eventually settled, in 1922, paying a substantial fee for licenses to use the Minerals Separation process. One unfortunate result of the dispute was professional divisiveness among the mining engineering community for a generation. In 1913, the Minerals Separation paid for a test plant for the Inspiration Copper Company at Miami, Arizona. Built under the San Francisco office director, Edward Nutter, it proved a success. Inspiration engineer
L. D. Ricketts ripped out a gravity concentration mill and replaced it with the Minerals Separation process, the first major use of the process at an American copper mine. A major holder of Inspiration stock were men who controlled the great Anaconda mine of Butte. They immediately followed the Inspiration success to build a Minerals Separation licensed plant at Butte, in 1915–1916, a major statement about the final acceptance of the Minerals Separation patented process. John M. Callow, of General Engineering of
Salt Lake City, had followed flotation from technical papers and the introduction in both the Butte and Superior Mill, and at Inspiration Copper in Arizona and determined that mechanical agitation was a drawback to the existing technology. Introducing a porous brick with compressed air, and a mechanical stirring mechanism, Callow applied for a patent in 1914 (some say that Callow, a Jackling partisan, invented his cell as a means to avoid paying royalties to Minerals Separation, which firms using his cell eventually were forced to do by the courts). This method, known as Pneumatic Flotation, was recognized as an alternative to the Minerals Separation process of flotation concentration. The
American Institute of Mining Engineers presented Callow the James Douglas Gold Medal in 1926 for his contributions to the field of flotation. By that time, flotation technology was changing, especially with the discovery of the use of xanthates and other reagents, which made the Callow cell and his process obsolete. Montana Tech professor
Antoine Marc Gaudin defined the early period of flotation as the mechanical phase while by the late 1910s it entered the chemical phase. Discoveries in reagents, especially the use of xanthates patented by Minerals Separations chemist Cornelius H. Keller, not so much increased the capture of minerals through the process as making it far more manageable in day-to-day operations. Minerals Separation's initial flotation patents ended 1923, and new ones for chemical processes gave it a significant position into the 1930s. During this period the company also developed and patented flotation processes for iron out of its Hibbing lab and of phosphate in its Florida lab. Another rapid phase of flotation process innovation did not occur until after 1960. In the 1960s the froth flotation technique was adapted for
deinking recycled paper. The success of the process is evinced by the number of claimants as "discoverers" of flotation. In 1961, American engineers celebrated "50 years of flotation" and enshrined James Hyde and his Butte & Superior mill. In 1977, German engineers celebrated the "hundredth anniversary of flotation" based on the brothers Bessel patent of 1877. The historic Glasdir copper mine site advertises its tours in Wales as site of the "discovery of flotation" based upon the Elmore brothers work. Recent writers, because of the interest in celebrating women in science, champion Carrie Everson of Denver as mother of the process based on her 1885 patent. Omitted from this list are the engineers, metallurgists and chemists of Minerals Separation, Ltd., which, at least in the American and Australian courts, won control of froth flotation patents as well as right of claimant as discoverers of froth flotation. But, as historian Martin Lynch writes, "Mineral Separation would eventually prevail after taking the case to the US Supreme Court [and the House of Lords], and in so doing earned for itself the cordial detestation of many in the mining world." Further improvements have come from Australia in the form of the
Jameson Cell, developed at the University of Newcastle, Australia in 1980s. It operates by the use of a plunging jet that generates fine bubbles. These fine bubbles have a higher kinetic energy and a smaller diameter. As such, they can be used for the flotation of fine grained particles.
Theory Froth flotation efficiency is determined by a series of probabilities: those of particle–bubble contact, particle–bubble attachment, transport between the pulp and the froth, and froth collection into the product launder. In a conventional mechanically-agitated cell, the void fraction (i.e. volume occupied by air bubbles) is low (5 to 10 percent) and the bubble size is usually greater than 1 mm. Consequently, several cells in series are required to increase the particle residence time, thus increasing the probability of particle–bubble contact. : \gamma_{lv} \cos \theta = (\gamma_{sv} - \gamma_{sl}) where: • γlv is the surface energy of the liquid/vapor interface • γsv is the surface energy of the solid/vapor interface • γsl is the surface energy of the solid/liquid interface, • θ is the
contact angle, the angle formed at the junction between vapor, solid, and liquid phases. Minerals targeted for separation may be chemically surface-modified with collectors so that they are more hydrophobic. Collectors are a type of
surfactant that increase the natural hydrophobicity of the surface, increasing the
separability of the hydrophobic and hydrophilic particles. Collectors either chemically bond via
chemisorption to the mineral or adsorb onto the surface via
physisorption.
IMFs and surface forces in bubble-particle interactions Collision The collision rates for fine particles (50 - 80 μm) can be accurately modeled, but there is no current theory that accurately models bubble-particle collision for particles as large as 300 μm, which are commonly used in flotation processes. For fine particles,
Stokes law underestimates collision probability while the potential equation based on
surface charge overestimates collision probability so an intermediate equation is used. It is important to know the collision rates in the system since this step precedes the adsorption where a three phase system is formed.
Adsorption (attachment) The effectiveness of a medium to adsorb to a particle is influenced by the relationship between the surfaces of both materials. There are multiple factors that affect the efficiency of adsorption in chemical, thermodynamic, and physical domains. These factors can range from surface energy and polarity to the shape, size, and roughness of the particle. In froth flotation, adsorption is a strong consequence of surface energy, since the small particles have a high surface area to size ratio, resulting in higher energy surfaces to form attractions with adsorbates. The air bubbles must selectively adhere to the desired minerals to elevate them to the surface of the slurry while wetting the other minerals and leaving them in the aqueous slurry medium. Particles that can be easily wetted by water are called hydrophilic, while particles that are not easily wetted by water are called hydrophobic. Hydrophobic particles have a tendency to form a separate phase in aqueous media. In froth flotation the effectiveness of an air bubble to adhere to a particle is based on how hydrophobic the particle is. Hydrophobic particles have an affinity to air bubbles, leading to adsorption. The bubble-particle combinations are elevated to the froth zone driven by buoyancy forces. For the following equations: • F is the weight percent of feed • C is the weight percent concentrate • T is the weight percent of tailings • c, t, and f are the
metallurgical assays of the concentrate, tailings, and feed, respectively Ratio of feed weight to concentrate weight \tfrac {F}{C} (unitless) : \frac{F}{C} = \frac{c-t}{f-t} Percent of metal recovered (\Chi_R) in wt
% :\Chi_R = 100\left(\frac{c}{f}\right)\left(\frac{f-t}{c-t}\right) Percent of metal lost (\Chi_L) in wt
% :\Chi_L = 100 - \Chi_R Percent of weight recovered \left(\Chi_W\right) in wt
% :\Chi_W = 100\left(\frac{C}{F}\right) = 100\frac{f-t}{c-t} This can be calculated using weights and assays, as \frac{Cc}{Ff}*100. Or, since \frac{C}{F} = \frac{f-t}{c-t}, the percent of metal recovered (\Chi_R) can be calculated from assays alone using \Chi_R = 100\left(\frac{c}{f}\right)\left(\frac{f-t}{c-t}\right). Percent of metal lost is the opposite of the percent of metal recovered, and represents the material lost to the tailings. == See also ==