Froth floatation

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, where it was one of the great enabling technologies of the 20th century. It has been described as "the single most important operation used for the recovery and upgrading of sulfide ores". The development of froth flotation has improved the recovery of valuable minerals, such as copper- and lead-bearing minerals. Along with mechanized mining, it has allowed the economic recovery of valuable metals from much lower grade ore than previously.

Descriptions of the use of a flotation process have been found in ancient Greek and Persian literature suggesting its antiquity. During the late nineteenth century, the process basics were discovered through a slow evolutionary phase; then, during the first decade of the twentieth century, a more rapid investigation of oils, froths, and agitation led to proven work-place applications, especially at Broken Hill, Australia, that brought the technological innovation known as “froth flotation.” During the early twentieth century, it truly and dramatically revolutionized -- an overworked term, but accurate here -- mineral processing around the globe.

Initially, naturally occurring chemicals such as fatty acids and oils were used as flotation reagents in a large quantity 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.

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 ever being field tested, let alone used commercially. While 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, because the Bessel process was used on graphite not gold, silver copper, lead, zinc, etc, their work has been ignored by most historians of the technology. Seventy-seven year old inventor Hezekiah Bradford of Philadelphia imitated their work and patented a similar process in 1885. He had received his first patent in 1834, primarily invented machinery to separate slate from coal during the 1850s-1860s, and perfected the Bradford Breaker, still in use by the coal industry today, but it is uncertain if his 1885 patented "flotation" process was successfully introduced in the graphite deposits in nearby Chester County, Pennsylvania.

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